bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopamine inhibits Na(+)-H+ exchanger activity in renal BBMV by stimulation of adenylate cyclase
Authors: Felder C. C. , Campbell T. , Albrecht F. , Jose P. A.
Published: December 2017

To determine a renal tubular mechanism for the natriuretic effect of dopamine (DA) and DA-1 agonists, we measured Na(+)-H+ exchange activity (amiloride sensitive) in rat renal cortical brush-border membrane vesicles (BBMV). Renal cortical tissues were preincubated with ligands before BBMV preparation to study Na(+)-H+ exchange activity in the absence of the added ligands that may compete for ion binding sites of the exchanger. DA and DA-1 agonist-inhibited Na(+)-H+ exchange activity was concentration and time dependent. The inhibitory effect was not due to increased permeability, collapse of the proton gradient, or change in vesicle size and did not extend to Na(+)-glucose symport. DA-2 agonists had no effect, whereas alpha-adrenergic agonists increased Na(+)-H+ exchange activity. Kinetic analysis revealed that the DA-1 agonist inhibited Na(+)-H+ exchange activity by a noncompetitive process. 2',5'-Dideoxyadenosine inhibited adenylate cyclase activity and reversed the inhibitory effect of DA-1 agonist on the exchanger. H4, an isoquinoline sulfonamide, which inhibits protein kinase A, also reversed the inhibitory effect of DA-1 agonist on the exchanger. Thus the DA-1 agonist-mediated inhibition of Na(+)-H+ exchange activity in BBMV is a receptor-mediated adenylate cyclase-linked process.
Inhibitory effect of phorbol ester on sodium transport in frog urinary bladder
Authors: Satoh T. , Endou H.
Published: December 2017

To confirm the role of protein kinase C (PKC) on epithelial Na transport, we studied the effects of phorbol 12-myristate 13-acetate (PMA) and dioctanoylglycerol (DiC8), activators of PKC, on short-circuit current (Isc) in frog urinary bladder and further examined the influence of sphingosine, an inhibitor of PKC, on PMA- or DiC8-modulated Isc. PMA reduced basal Isc in a dose-dependent manner, and sphingosine (10 and 100 microM) partially restored PMA-reduced Isc. On the other hand, DiC8 (5 x 10(-5) M) also reduced basal Isc, and this action was completely prevented by 100 microM sphingosine. Both PMA (4 x 10(-5) M) and DiC8 inhibited vasopressin (50 mU/ml)- and forskolin (5 x 10(-5) M)-stimulated increases in Isc. PMA (4 x 10(-5) M) also inhibited 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP)-stimulated increase in Isc. Furthermore, PMA (4 x 10(-5) M) and DiC8 (5 x 10(-5) M) inhibited vasopressin (50 mU/ml)-stimulated cAMP accumulation. DiC8 also inhibited forskolin-stimulated cAMP accumulation. These results indicate that PMA exerts inhibitory influence on Na transport mainly by its own potency of PKC activation. In addition, it is suggested that there is a cross talk in epithelial Na transport between PKC and cAMP-dependent pathway in frog urinary bladder.
Regional localization of renal Na(+)-H+ antiporter: response to respiratory acidosis
Authors: Ruiz O. S. , Talor Z. , Arruda J. A.
Published: December 2017

The Na(+)-H+ antiporter of renal brush-border membranes has been well characterized and plays a role in adaptation to acidosis. Na(+)-H+ antiporter activity has been described in other renal regions, but its kinetics as well as its role in adaptation to acidosis are unclear. Thus we measured Na(+)-H+ antiporter activity in membrane vesicles of outer and inner stripes of outer medulla (OSOM and ISOM, respectively) and in plasma membranes from papilla and compared it to Na(+)-H+ antiporter activity of the cortex in control and hypercapnic rabbits. Chronic hypercapnia (induced by exposure to CO2 for 48 h) was associated with significantly higher PCO2 and plasma HCO3- and lower urine pH than controls. In control animals, magnitude of Vmax of amiloride-sensitive component of Na(+)-H+ antiporter (expressed as fluorescence units.300 micrograms protein-1.min-1) was 392.2 +/- 32 in cortex, 115 +/- 9.7 in OSOM, 66.1 +/- 9.4 in 15-25% (F1) fraction and 118.7 +/- 16.8 in 25-40% (F2) fraction of ISOM, respectively, and 79.3 +/- 5.2 in papilla. These values were significantly different from each other except between F1 and papilla and F2 and OSOM. The Km for Na, however, was not different, suggesting that the renal Na(+)-H+ antiporter is basically the same in different renal regions but displays different activity. Hypercapnia for 48 h increased significantly the amiloride-sensitive component of Na(+)-H+ antiporter by 60% in cortex, 43% in F1, and 29% in papilla but failed to alter Vmax in OSOM.(ABSTRACT TRUNCATED AT 250 WORDS)
Bilitranslocase localization and function in basolateral plasma membrane of renal proximal tubule in rat
Authors: Elias M. M. , Lunazzi G. C. , Passamonti S. , Gazzin B. , Miccio M. , Stanta G. , Sottocasa G. L. , Tiribelli C.
Published: December 2017

Bilirubin and phthalein dyes are taken up by the liver via a carrier-mediated mechanism operated at least in part by bilitranslocase (BTL). Because they also undergo renal transport, the presence and function of BTL was investigated in rat renal tubular plasma membrane vesicles. Transport of sulfobromophthalein (BSP) was enriched in basolateral domain of plasma membrane and followed the distribution pattern of Na(+)-K(+)-ATPase but not of gamma-glutamyltransferase. BSP uptake was inhibited by addition of monospecific antibodies raised against hepatic BTL. As in liver vesicles, BSP transport was electrogenic, being greatly accelerated by addition of valinomycin in presence of an inwardly directed K+ gradient. Apparent Km of BSP transport was 17 +/- 2 microM (n = 3 expts), one order of magnitude higher than that measured in liver; however, Vmax was similar to that described in liver vesicles (429 +/- 18 nmol BSP.mg protein-1.min-1, n = 3 expts). Competitive inhibition was observed with both unconjugated bilirubin (Ki, 2.9 +/- 0.2 microM) and rifamycin SV (Ki, 76 +/- 10 microM), known competitors for hepatic BTL-mediated transport of BSP. Immunoblotting studies with anti-BTL monospecific antibodies revealed presence of a single positive band only in basolateral-enriched membrane fraction; its apparent molecular mass was 37 kDa, virtually identical to that of hepatic protein. Immunohistochemistry confined presence of BTL to renal proximal tubules (RPT) We conclude that BTL is present in basolateral plasma membrane of RPT cells. Lower affinity of renal, compared with hepatic protein, for substrates might explain the marginal role of kidney in plasma clearance of bilirubin and cholephilic dyes.
Renal atrial natriuretic peptide receptor subtypes in spontaneously hypertensive rats
Authors: Brown J. , Salas S. P. , Polak J. M.
Published: December 2017

Receptor subtypes for atrial natriuretic peptide (ANP) were characterized in kidneys of 18-wk-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) by in vitro autoradiography through use of des[Gln18, Ser19, Gly20, Leu21, Gly22] ANP-(4–23) (C-ANP) and ANP-(5–25) as subtype-selective ligands. alpha-125I-ANP (100 pM) bound reversibly but with high affinity to glomeruli, to stripes in outer medulla, and to inner medulla of both WKY and SHR. C-ANP (10 microM) inhibited approximately 70% of the glomerular binding but none of the medullary binding in either strain. All high-affinity specifically reversible binding sites for alpha-ANP that bound C-ANP were also bound by 10 microM ANP-(5–25). However, the specifically reversible binding of alpha-125I-ANP that was not inhibited by 10 microM C-ANP behaved differently in each strain. In WKY, this binding was weakly inhibited by ANP-(5–25), so that even the presence of 10 microM ANP-(5–25) did not inhibit some glomerular binding and greater than 40% of the specifically reversible medullary binding of alpha-125I-ANP. In SHR, this binding was inhibited by ANP-(5–25) with a significantly higher affinity so that all specifically reversible binding of alpha-125I-ANP was inhibited by 10 microM ANP-(5–25). SHR also showed higher affinities but lower maximum binding capacities for alpha-ANP in their outer cortical glomeruli and medullas. These results suggest that the preponderant medullary ANP receptor differs between WKY and SHR. Differences in glomerular subtypes of ANP receptor may also distinguish WKY and SHR.
Apical and basolateral membrane H+ extrusion mechanisms in inner stripe of rabbit outer medullary collecting duct
Authors: Hays S. R. , Alpern R. J.
Published: December 2017

To examine mechanisms of H+ extrusion in the inner stripe of outer medullary collecting duct (OMCDIS), cell pH (pHi) was measured microfluorometrically in in vitro perfused tubules by use of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In total absence of luminal and peritubular Na+, pHi recovery from an acid load (NH3/NH+4 pulse) occurred at an initial rate of 0.13 +/- 0.02 pH units/min, whereas in the presence of 135 mM peritubular Na+, pHi recovered at 1.40 +/- 0.28 pH units/min. Na(+)-dependent pHi recovery was completely inhibited by 1.0 mM peritubular amiloride. Luminal Na+ (135 mM) addition had no effect on pHi recovery. Na(+)-independent pHi recovery from acid load was manifest by a triphasic response: 1) initial slow alkalinization; 2) slow cell acidification; and 3) a final phase that exhibited gradually increasing rates of alkalinization, returning pHi above the initial control level (pre-NH3/NH+4 pulse). Luminal N-ethylmaleimide (NEM, 500 microM), an H(+)-ATPase inhibitor, significantly inhibited initial rate of pHi recovery and total pHi recovery; whereas 500 microM peritubular NEM had no effect on initial rate of pHi recovery. Luminal SCH 28080 (100 microM), an H(+)-K(+)-ATPase inhibitor, had no effect on initial rate of pHi recovery or total pHi recovery. Thus rabbit OMCDIS possesses both an apical membrane NEM-sensitive, SCH 28080-insensitive, Na(+)-independent H+ extrusion mechanism (likely a simple H(+)-translocating ATPase) and a basolateral membrane amiloride-sensitive Na(+)-H+ antiporter.
Thapsigargin demonstrates calcium-dependent regulation of phosphate uptake in HeLa cells
Authors: Middleton J. P. , Albers F. J. , Dennis V. W. , Raymond J. R.
Published: December 2017

We used thapsigargin, a sesquiterpene lactone that mobilizes intracellular Ca without increases in inositol phosphates or major activation of protein kinase C (PKC), to test the specific effects of increasing cytosolic Ca on Na-dependent phosphate uptake in HeLa cells. Thapsigargin increased the Vmax for phosphate uptake from 5.40 +/- 0.26 to 7.86 +/- 0.43 nmol.mg protein-1.3 min-1 (n = 7, P less than 0.001) without change in the apparent Km for phosphate, which averaged 0.15 +/- 0.02 mM. The effect of thapsigargin was dependent on concentration and time. Inactivation of PKC by overnight exposure to 16 microM phorbol 12,13-dibutyrate did not eliminate the effect of thapsigargin, although it completely abolished the effects of phorbol ester on phosphate uptake. Thus thapsigargin are not dependent on PKC. As in other cell systems, thapsigargin increased cytosolic Ca concentration. Removal of extracellular Ca diminished the increase in cytosolic Ca and eliminated the effect of thapsigargin on phosphate uptake. Collectively, our data indicate that Na-dependent phosphate uptake in HeLa cells can be regulated by at least three specific signaling pathways: protein kinase A, PKC, and increased cytosolic Ca.
Reduction of cerebral NaCl concentration can abolish mineralocorticoid escape
Authors: Pennington G. L. , McKinley M. J.
Published: December 2017

The effect of lowering cerebrospinal fluid (CSF) Na concentration on renal Na excretion (UNaV) was investigated in conscious sheep undergoing mineralocorticoid escape induced by intravenous infusion of aldosterone (20 micrograms.ml-1.h-1) for 3 days. On the 3rd day of aldosterone administration, when plasma and CSF Na concentration and mean arterial blood pressure (MABP) were increased as a result of the mineralocorticoid treatment, a reduction in the CSF Na concentration was induced by infusing a Na-free solution of 300 mmol/l mannitol (1 ml/h) into a lateral cerebral ventricle. This caused significant reductions in UNaV and MABP and a significant increase in renal free water clearance (CH2O). There was no significant change in glomerular filtration rate or plasma atrial natriuretic peptide concentration, but renal lithium clearance decreased. Simultaneous intravenous infusion of vasopressin (0.03 microgram/h) and lowering of CSF Na concentration also caused significant reductions in UNaV and MABP, but CH2O did not increase. We propose that increased Na concentration of brain fluid may initiate natriuretic and pressor mechanisms contributing to the process of mineralocorticoid escape. Reduced UNaV may have been due to reduced MABP, but it is unlikely to have been due to reduced plasma vasopressin levels.
Angiotensin II regulates renin gene expression
Authors: Johns D. W. , Peach M. J. , Gomez R. A. , Inagami T. , Carey R. M.
Published: December 2017

We investigated the effect of angiotensin II (ANG II) and enalapril on accumulation of renin messenger RNA (mRNA) and on renal renin distribution (immunohistochemical analysis). Adult Wistar-Kyoto rats received enalapril (0.2 mg/ml) in distilled drinking water for 8 or 12 days. On day 5 of enalapril treatment, an osmotic minipump was implanted in the peritoneum that caused sustained release of ANG II (200 ng.kg-1.min-1) or vehicle (bovine serum albumin) for 3 or 7 days. Control rats received water for 8 or 12 days and osmotic minipump implantation (containing vehicle solution) on the 5th day. Renin mRNA was identified by hybridization with a 32P-labeled full-length complementary DNA and was detected by autoradiography. Enalapril treatment increased renal renin mRNA specific activity (renin mRNA/total RNA). Subsequent infusion of angiotensin II for 3 or 7 days decreased renal renin mRNA specific activity. In addition, renin immunostaining increased along the afferent arteriole after enalapril treatment; however, enalapril-induced spread of renin immunostaining was not inhibited by ANG II. Thus ANG II attenuates the accumulation of renin mRNA stimulated by enalapril treatment without alteration of renal renin distribution. The lack of effect of ANG II on renal renin distribution may be due to the length of turnover time for stored protein. These findings suggest the shortloop negative feedback of ANG II on renin reflects inhibition of renin synthesis by ANG II. Therefore, we propose that ANG II exerts a direct inhibitory effect on renin by regulation of renin gene expression in renal vasculature.
Branched-chain amino acids augment neither albuminuria nor albumin synthesis in nephrotic rats
Authors: Kaysen George A. , Al-Bander Hamoudi , Martin Victor I. , Jones Hardin , Hutchison Florence N.
Published: December 2017

Both albuminuria (UalbV) and albumin synthesis (AlbSyn) are modulated by dietary protein in nephrotic rats, but the agent(s) linking diet to altered UalbV and AlbSyn is unknown. Others have reported that branched-chain amino acids (BCAA) cause neither increased renal blood flow nor glomerular filtration rate (GFR) normally induced by dietary protein nor increased blood glucagon thought to be necessary for protein-mediated effects on renal hemodynamics. The effect of BCAA on UalbV is unknown. Because BCAA increase AlbSyn in tissue culture and after a fast, it is possible that feeding BCAA may increase AlbSyn but not UalbV in nephrosis. Nephrotic rats were fed either 8.5% casein (LP); 21% casein (NP); 8.5% casein supplemented with valine, leucine, and isoleucine to the total amount provided by a 21% casein diet (2.37%) (LBC); or 8.5% casein plus 12.5% BCAA providing a diet isonitrogenous to 21% casein (HBC). UalbV and AlbSyn were significantly greater in NP compared with LP, LBC, or HBC and were the same in the latter three groups. Glucagon was infused into nephrotic rats fed 8.5% casein either subcutaneously or intraperitoneally in quantities sufficient to increase plasma levels to over 10 times control but had no effect on UalbV. The ability of dietary protein to increase AlbSyn or UalbV is not a result of total -amino nitrogen intake but is a result of the specific amino acid composition of the diet and must result entirely from the effect of one or more non-BCAA. Increased blood glucagon alone has no effect on UalbV.

permselectivity; nephrotic syndrome; proteinuria; glucagon; corticosterone; Heymann nephritis

Submitted on June 26, 1990

Accepted on October 3, 1990
Abundance of Na(+)-K(+)-ATPase mRNA is regulated by glucocorticoid hormones in infant rat kidneys
Authors: Celsi G. , Nishi A. , Akusjarvi G. , Aperia A.
Published: December 2017

The administration of glucocorticoid hormone (GC) accelerates the postnatal maturation of renal Na(+)-K(+)-ATPase activity. This study examines the role of GC for the regulation of the Na(+)-K(+)-ATPase mRNA abundance in renal cortex during development. In 12- to 14-day-old rats an upsurge in serum GC concentration was accompanied by an increase in Na(+)-K(+)-ATPase activity and by an apparent increase in mRNA abundance. In 10-day-old rats injected with a single intraperitoneal dose of betamethasone (T) or diluent (C) the abundances of alpha 1- and beta-mRNAs were 1.8- to 2-fold higher in T than in C rats after 20 min. The mRNA abundance of both subunits was threefold higher after 1 h (P less than 0.01), and it was six- to sevenfold higher after 6 h (P less than 0.01). In any given sample there was a coordinate change in alpha 1- and beta-mRNAs relative to C rats. GC did not appear to induce the expression of any alternative catalytic subunit. The alpha 2-mRNA was not detectable in any experimental protocol. Furthermore, the ouabain inhibition of the Na(+)-K(+)-ATPase, partially purified from the renal cortex, was the same before and after GC. In adult rats injected with betamethasone neither the alpha 1- nor the beta-mRNA abundance was different at any time after injection from those in adult C rats. The rapid onset of the GC effect on mRNA abundance in infant rats suggests that the hormone directly activates the gene for Na(+)-K(+)-ATPase alpha 1-subunit, as well as beta-subunit in the developing kidney, and that GC thereby plays an important role for the postnatal maturation of the kidney.
Volume regulatory Cl- loss after Na+ pump inhibition in CCT principal cells
Authors: Strange K.
Published: December 2017

Ouabain caused rabbit cortical collecting tubule (CCT) principal cells to swell 53% and then undergo regulatory volume decrease (RVD) at a rate of 4%/min to a new steady-state volume 10% below control. Reduction of peritubular Cl- concentration transiently depolarized transepithelial potential (Vte) by 36 mV and stimulated the rate of RVD 30-fold. Peritubular application of 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibited RVD 74%. In contrast, luminal Cl- reduction or application of DIDS had no effect on RVD. A 10-fold elevation of perfusate K+ caused volume-regulated cells to swell 23% at a rate of 60%/min. Removal of luminal Cl- had no effect on either the rate or magnitude of K+ swelling. Peritubular or bilateral Cl- removal, however, inhibited the rate of K+ swelling by 96 and 99%, respectively. Substitution of bath Cl- for Br-, SCN-, or I- inhibited the rate of K+ swelling by 40, 38, and 98%, respectively. Surprisingly, NO3- inhibited the rate of K+ swelling by 82%. All Cl- substitutes tested transiently depolarized Vte by 3–49 mV. These results suggest strongly that RVD is mediated by a basolateral Cl- channel with a high selectivity for Cl- over other anions.
Increased renal endothelin production in rats with reduced renal mass
Authors: Benigni A. , Perico N. , Gaspari F. , Zoja C. , Bellizzi L. , Gabanelli M. , Remuzzi G.
Published: December 2017

Renal endothelin (ET) production was investigated in rats after renal mass ablation, a model of progressive renal disease characterized by glomerular hemodynamic alterations and capillary thrombosis, and in sham-operated animals. Thrombin stimulation of renal cortical tissue from rats with renal mass reduction, 45 but not 7 days after surgery, generated significantly (P less than 0.01) more ET than tissue from sham-operated animals. Exposure to thrombin of isolated glomeruli from remnant but not sham kidneys also significantly (P less than 0.01) increased ET production compared with unstimulated glomeruli. At day 45, in rats with renal mass ablation ET plasma levels were numerically lower, whereas urinary excretion rate of ET was significantly (P less than 0.01) increased compared with sham-operated animals. After a 50-min intravenous infusion of 125I-ET to normal rats and animals with renal mass ablation, less than 0.3% and 0.03%, respectively, of total infused radioactivity was recovered in urine. These results indicate that thrombin-stimulated ET production by renal cortical tissues is increased in rats with renal mass reduction. Despite normal or low-normal plasma ET levels, urinary excretion of the peptide is markedly increased in this model. The exogenously labeled ET added to circulation is not excreted by the kidney, suggesting that enhanced urinary excretion rate would reflect an increased renal production of the peptide in rats with remnant kidney.
A pertussis toxin-sensitive GTP-binding protein couples endothelin to phospholipase C in rat mesangial cells
Authors: Thomas C. P. , Kester M. , Dunn M. J.
Published: December 2017

The mechanisms of stimulation of phospholipase C (PLC) by endothelin, specifically the role of guanine nucleotide-binding proteins (GTP-binding proteins) in coupling the endothelin receptor to PLC, were investigated in rat mesangial cells. Endothelin-1 (ET) synergistically released inositol polyphosphates in the presence of the stimulatory GTP analogue guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) in permeabilized cells. In addition, in intact cells, pertussis toxin partially inhibited the stimulation of total inositol phosphates (IPn) by ET. Pertussis toxin also reduced the peak ET-stimulated intracellular free calcium level ([Ca2+]i) in these cells, both in the presence and absence of extracellular calcium. Pertussis toxin induced ADP ribosylation of a 41- to 43-kDa protein in mesangial cell membranes, and this effect was inhibited by prior exposure to ET and augmented by the inhibitory GDP analogue, guanosine 5'-O-(2-thiodiphosphate) (GDP beta S). Thus a pertussis toxin-sensitive GTP-binding protein is involved in the activation of PLC by ET in glomerular mesangial cells.
Role of intracellular calcium in volume regulation by rabbit medullary thick ascending limb cells
Authors: Montrose-Rafizadeh C. , Guggino W. B.
Published: December 2017

Previous studies demonstrated that Ca2(+)-activated K+ channels in luminal membrane of rabbit medullary thick ascending limb cells (MTAL) are activated on exposure of the cells to hyposmotic solutions [J. Taniguchi and W. B. Guggino. Am. J. Physiol. 257 (Renal Fluid Electrolyte Physiol. 26): F347-F352, 1989]. In this study, we investigated the mechanism of activation of Ca2(+)-activated K+ channels in MTAL cells exposed to hyposmotic solutions. MTAL cells swell in hyposmotic medium and regulate volume back toward the starting volume. This regulatory volume decrease (RVD) is inhibited at high medium K+ concentrations or by presence of quinine or Ba2+ in extracellular medium, suggesting involvement of K+ channels. Measurements of intracellular Ca2+ concentrations with fura-2 show that intracellular Ca2+ rises in hyposmotic solutions and that this rise does not occur in absence of extracellular Ca2+. Nifedipine and verapamil also inhibit rise in intracellular Ca2+. Decreasing intracellular Ca2+ by removal of external Ca2+ in presence of EDTA or by chelation of intracellular Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) inhibits RVD. We conclude that hypotonic solutions activate K+ efflux probably via K+ channels and Ca2+ influx via a nifedipine- and verapamil-sensitive pathway. Lowering intracellular Ca2+ removes the ability of MTAL cells to regulate volume in hyposmotic solutions.
Characterization of endothelin 1 receptor and signal transduction mechanisms in rat medullary interstitial cells
Authors: Wilkes B. M. , Ruston A. S. , Mento P. , Girardi E. , Hart D. , Vander Molen M. , Barnett R. , Nord E. P.
Published: December 2017

Previous autoradiographic studies have delineated the renal medullas the predominant site of renal endothelin (ET) receptors. Accordingly, cultured rat renal medullary interstitial cells (RMICs) were studied as a target tissue for ET action. Scatchard analysis revealed presence of a single class of high-affinity receptor sites (Kd, 57 +/- 10 pM; receptor density, 749 +/- 124 fmol/mg protein). Relative potency order for displacing 125I-ET-1 was ET-1 greater than ET-2 greater than sarafotoxin greater than big endothelin (human) = big endothelin (porcine). ET-3, unrelated pressor substances, vasodilators, Ca2+ channel antagonists, atrial natriuretic factor, GTP, and GppNHp did not inhibit binding. Challenge of monolayers with ET-1 evoked a biphasic elevation in cytosolic free Ca2+ concentration [Ca2+]i). Initial transient rise in [Ca2+]i observed in absence of extracellular Ca2+ and accumulation of inositol trisphosphate (IP3) was consistent with activation of phosphatidylinositol-specific phospholipase C (PI-PLC). Half-maximal activation concentration of ET-1 for the process was 0.5 and 1 nM for [Ca2+]i and IP3, respectively. The late sustained phase in [Ca2+]i elevation was completely blocked by Ni2+, unperturbed by nimodipine, and accompanied by influx of Mn2+, indicating presence of receptor-operated Ca2+ channels. Ca2+ channel opening was detected at 10(-16) MET-1, whereas greater than 10(-12) M agonist was required to mobilize Ca2+ from intracellular stores and/or stimulate phosphoinositol hydrolysis, indicating that ET activation of PI-PLC and Ca2+ channel opening were independent events. ET-1 markedly stimulated prostaglandin E2 synthesis in a concentration-dependent manner that paralleled PI-PLC activation and mobilization of [Ca2+]i. In summary, cultured rat RMICs possess ET receptors that are linked to PI-PLC, Ca2+ channels, and perhaps phospholipase A2.
Renal synthesis of atriopeptin-like protein in physiology and pathophysiology
Authors: Greenwald J. E. , Needleman P. , Wilkins M. R. , Schreiner G. F.
Published: December 2017

Atriopeptin is synthesized in mammalian atria as a 126-amino acid (14 kDa) prohormone, but it is secreted and circulates as a 28-amino acid (2.5 kDa) peptide. We have demonstrated the synthesis and secretion of an atriopeptin-like peptide in neonatal and adult rat kidney cell cultures. In this study, we evaluated the site of renal synthesis of this protein and its expression in normal rats and rats made nephrotic with puromycin aminonucleoside. The major form of atriopeptin in normal kidneys comigrated with an apparent molecular mass of 2.5 kDa assessed by gel filtration chromatography. However, the major form of this atriopeptin-like protein in nephrotic kidneys was determined to have an apparent molecular mass similar to the heart prohormone. No atriopeptin prohormone was detected in the plasma of nephrotic rats. Localization of this renal atriopeptin-like protein was accomplished by immunocytochemistry of rat kidney frozen sections. Using an antibody generated against either the COOH-terminal or NH3-terminal region of the cardiac atriopeptin prohormone, we detected specific immunostaining in the distal cortical nephron of the nephrotic kidney. This is the first report of the anatomic localization of a renal atriopeptin-like protein and its upregulation in nephrosis.
Dietary calcium modulates renal BBM angiotensin II binding and Na(+)-H+ antiporter activity in SHR
Authors: Levi M. , Henrich W. L.
Published: December 2017

Dietary Ca is an important modulator of blood pressure in the spontaneously hypertensive rat (SHR). Since the kidney plays a key role in the pathogenesis of hypertension, the purpose of this study was to determine the potential renal mechanisms of the blood pressure-lowering effect of increasing dietary Ca content. In 21-day-old SHR fed 0.1 vs. 3.6% Ca diet for 14 days, increasing dietary Ca had no significant effects on basal [704 +/- 50 in 0.1% Ca vs. 784 +/- 61 ng angiotensin I (ANG I).mg-1.h-1 in 3.6% Ca, P = not significant (NS)], isoproterenol-stimulated (1,057 +/- 52 in 0.1% Ca vs. 1,104 +/- 59 ng ANG I.mg-1.h-1 in 3.6% Ca, P = NS), or angiotensin II (ANG II)-inhibited (370 +/- 50 in 0.1% Ca vs. 411 +/- 39 ng ANG I.mg-1.h-1 in 3.6% Ca, P = NS) renal superficial cortical slice renin release. In contrast, in apical brush-border membrane (BBM) vesicles isolated from the superficial cortex, increasing dietary Ca caused a significant decrease in ANG II binding, which was mediated by a decrease in the number of binding sites (Bmax, 376 +/- 14 in 0.1% Ca vs. 234 +/- 6 fmol ANG II/mg BBM protein in 3.6% Ca, P less than 0.01), and no change in the affinity [dissociation constant (Kd), 17.8 +/- 1.4 in 0.1% Ca vs. 13.4 +/- 2.8 nM ANG II in 3.6% Ca, P = NS].(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic intrarenal hyperinsulinemia does not cause hypertension
Authors: Hall J. E. , Brands M. W. , Mizelle H. L. , Gaillard C. A. , Hildebrandt D. A.
Published: December 2017

Hyperinsulinemia has been postulated to link obesity and hypertension via the antinatriuretic actions of insulin. The main goal of this study was to quantitate the importance of the direct intrarenal actions of insulin, independent of systemic effects, in altering blood pressure and renal function. This was accomplished by determining the responses to chronic intrarenal insulin infusion in uninephrectomized, chronically instrumented conscious dogs maintained on a 74 meq/day sodium intake. Insulin was infused at rates calculated to raise intrarenal, but not systemic, insulin to levels similar to those observed in obese hypertensive dogs. Intrarenal insulin infusion (0.6 mU.kg-1.min-1) for 7 days caused transient decreases in sodium excretion but no significant changes in potassium excretion. Mean arterial pressure did not change during 7 days of insulin infusion, averaging 93 +/- 4 mmHg during control and 93 +/- 3 mmHg during insulin infusion. Intrarenal insulin caused small increases in GFR but no significant changes in effective renal plasma flow or renal vascular resistance. These results demonstrate that insulin causes transient decreases in sodium excretion, but chronic intrarenal hyperinsulinemia does not elevate blood pressure in normal dogs. Additional factors other than the direct sodium-retaining effects of insulin may be important in raising blood pressure in obesity-associated hypertension.
Role of kinins and angiotensin II in the renal hemodynamic response to captopril
Authors: Mattson D. L. , Roman R. J.
Published: December 2017

This study examined the role of angiotensin II (ANG II), kinins, and prostaglandins in the renal hemodynamic response to captopril in Munich-Wistar rats in which plasma renin activity was elevated [18.8 +/- 3.3 ng angiotensin I (ANG I).ml-1.h-1]. Neural influences on the kidney were eliminated by renal denervation, and renal perfusion pressure (RPP) was controlled using a clamp on the aorta. Urine flow, sodium excretion, renal blood flow (RBF), glomerular filtration rate (GFR), and cortical and papillary red blood cell (RBC) flow increased significantly after captopril (2 mg/kg iv). Glomerular and peritubular capillary pressures rose by 20%, and vasa recta capillary pressure fell by 3-4 mmHg due to significant reductions in estimated preglomerular, efferent arteriolar and renal capillary-venous vascular resistances. Infusion of ANG II (20 ng.kg-1.min-1 iv) returned RBF, GFR, and glomerular and peritubular capillary pressures to control; however, ANG II did not lower papillary RBC flow before inhibition of prostaglandin synthesis. Saralasin had no effect on papillary RBC flow or the response to captopril. The changes in vasa recta hemodynamics produced by captopril were blocked by a kinin antagonist. These findings indicate that ANG II exerts a vasoconstrictor influence on the renal cortical vasculature of Munich-Wistar rats; however, its effects on the medullary circulation are opposed by vasodilatory eicosanoids. They also suggest that kinins participate in the papillary RBC flow response to captopril, perhaps by reducing the outflow resistance from the vasa recta circulation.
Insulin increases Na(+)-H+ exchange activity in proximal tubules from normotensive and hypertensive rats
Authors: Gesek F. A. , Schoolwerth A. C.
Published: December 2017

The effects of insulin on Na(+)-H+ exchange were examined in isolated proximal segments from normotensive Sprague-Dawley (SD) and Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), with monitoring of rates of intracellular pH change (delta pHi/min) and ethylisopropyl amiloride (EIPA)-suppressible 22Na+ uptakes. A 12-min insulin preincubation was necessary for steady-state 22Na+ uptake and rate of pHi change. Insulin responses were similar for 4-wk (prehypertensive) SHR and WKY tubules; 8- (rising hypertension) and 16-wk (established hypertension) SHR responses were increased (P less than 0.05) 23 and 36% with 10(-6) M insulin, respectively. Insulin-like growth factors (IGF-I, IGF-II; 10(-10)-10(-7) M) had no effect on Na(+)-H+ exchange activity. Incubation with physiological concentrations of insulin in combination with hormones that stimulate Na(+)-H+ exchange (angiotensin II; alpha-adrenoceptor agonists) demonstrated no synergistic increases in SHR or WKY tubules; incubation with hormones that inhibit Na(+)-H+ exchange [parathyroid hormone (PTH), dopamine (DA)] indicated that insulin stimulation was decreased with PTH or DA in WKY segments, but PTH or DA reduction of insulin stimulation was lacking in SHR tubules. In summary, these data indicate a direct stimulation by insulin of Na(+)-H+ exchange in the proximal nephron, indicate an increased responsiveness in SHR compared with WKY tubules, and suggest a modulatory role of insulin with other hormones in regulating proximal nephron Na(+)-H+ exchange.
11 beta-Hydroxysteroid dehydrogenase mRNA expression in rat kidney
Authors: Yau J. L. , Van Haarst A. D. , Moisan M. P. , Fleming S. , Edwards C. R. , Seckl J. R.
Published: December 2017

11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) protects nonspecific renal mineralocorticoid receptors from exposure to circulating glucocorticoid in vivo by catalyzing the conversion of corticosterone to inactive 11-dehydrocorticosterone. Although 11 beta-OHSD bioactivity and aldosterone binding sites are found in distal tubular cells, mineralocorticoid receptor and 11 beta-OHSD immunoreactivities are not colocalized. However, there are several kidney isoforms of 11 beta-OHSD, not all of which may be immunoreactive, whereas only a single mRNA species has been described. Using in situ hybridization we found 11 beta-OHSD mRNA is highly expressed in all renal tubular epithelia in the rat. It is therefore likely that 11 beta-OHSD is colocalized with mineralocorticoid receptors in distal tubular cells.
Role of mineralocorticoids in adaptation of rabbit cortical collecting duct after loss of renal mass
Authors: Vehaskari V. M. , Herndon J.
Published: December 2017

The mechanism of compensatory adaptation and hypertrophy of the cortical collecting duct (CCD) was studied by in vitro microperfusion technique after surgical loss of functioning nephrons in the rabbit. Sodium transport was increased at 1 wk (lumen-to-bath sodium transport of 127 +2- 9 vs. 61 +/- 11 pmol.mm-1.min-1 in sham-operated animals, P less than 0.01) and 3 wk (111 +/- 19 vs. 54 +/- 7 pmol.mm-1.min-1, P less than 0.05) but not 16 h (81 +/- 13 vs. 78 +/- 8 pmol.mm-1.min-1) after loss of renal mass. The functional adaptation was accompanied by an increase in the size of the CCD. A rise in plasma aldosterone levels preceded and accompanied the increased sodium transport rate. Adrenalectomy at the time of reduction of renal mass totally prevented the development of both hypertrophy and sodium transport adaptation (sodium transport 15 +/- 8 pmol.mm-1.min-1). When adrenalectomy was combined with clamping the plasma aldosterone level in the nonstressed physiological range, compensatory hypertrophy and adaptation also failed to develop (sodium transport, 66 +/- 10 pmol.mm-1.min-1), but with high-dose aldosterone replacement both the hypertrophy and adaptation of sodium transport (130 +/- 23 pmol.mm-1.min-1) were restored. The results document the importance of increased mineralocorticoid activity in the development of compensatory hypertrophy and adaptation of sodium transport in rabbit CCD after loss of renal mass.
K(+)-ATPase-mediated Rb+ transport in rat collecting tubule: modulation during K+ deprivation
Authors: Cheval L. , Barlet-Bas C. , Khadouri C. , Feraille E. , Marsy S. , Doucet A.
Published: December 2017

To evaluate the involvement of K(+)-ATPase activity in K+ transport in the terminal segments of the rat nephron, we searched for the existence of a component of Rb+ uptake into microdissected segments of collecting tubule associated with the activity of this ATPase. Results indicated that K(+)-ATPase is stimulated by K+ and by Rb+ in a similar fashion and that it is specifically inhibited by the imidazopyridine Sch 28080 (apparent affinity approximately 5 x 10(-7) M). In both cortical and outer medullary collecting tubules (CCT and MCT) of normal rats, 10(-4) M Sch 28080 significantly inhibited the initial rate of Rb+ uptake. Sch 28080-sensitive Rb+ uptake in these two nephron segments was not altered by ouabain, as K(+)-ATPase activity. Finally, both K(+)-ATPase activity and Sch 28080-sensitive Rb+ uptake were increased by similar factors in the CCT and MCT of rats fed a K(+)-depleted diet for 3 days. In these two nephron segments, the apparent stoichiometry of K(+)-ATPase was 1 Rb+:1 ATP. These results demonstrate that K(+)-ATPase reflects the activity of a K+ pump that is pharmacologically similar to the gastric H(+)-K+ pump.
Effect of volume expansion on papillary blood flow and sodium excretion
Authors: Fenoy F. J. , Roman R. J.
Published: December 2017

The present study examined whether changes in plasma oncotic pressure or hematocrit play a role in the redistribution of renal blood flow and the natriuretic response to extracellular fluid volume (ECFV) expansion with saline. Intravenous infusion of saline produced a 46% increase in the flow of red blood cells (RBCs) in the papilla of Inactin-anesthetized euvolemic Munich-Wistar rats (n = 6). This was primarily due to an increase in the number of functional capillaries perfused with moving RBCs, as indicated both by laser-Doppler flowmetry and videomicroscopy. The velocity of RBCs in ascending or descending vasa recta was not significantly altered by the infusion of saline. Plasma volume expansion with a 6% solution of albumin (n = 6) did not increase papillary RBC flow, whereas volume expansion with whole blood produced a 17% increase in the flow of RBCs in the papilla. Sodium excretion after ECFV expansion with saline (n = 6) was greater than that seen after plasma volume expansion with a 6% solution of albumin (n = 5). The results indicate that the rise in papillary RBC flow after ECFV expansion with saline is due to an increase in the number of perfused vasa recta capillaries. The failure of plasma volume expansion to alter papillary RBC flow suggests that changes in plasma oncotic pressure and/or renal interstitial pressure may signal the rise in papillary RBC flow after intravenous infusion of saline. The present study also indicates that laser-Doppler flowmetry is a useful technique to monitor changes in the flow, velocity, and concentration of moving RBCs in tissue.
Renal action of progesterone and 18-substituted derivatives
Authors: Rafestin-Oblin M. E. , Couette B. , Barlet-Bas C. , Cheval L. , Viger A. , Doucet A.
Published: December 2017

The recently synthesized progesterone (P) derivatives, 18-vinylprogesterone (18VP) and 18-ethynylprogesterone (18EP), are potent inhibitors of aldosterone synthesis by adrenal glands. To evaluate the potential interest of these compounds as antihypertensive drugs, we determined whether they also interact with renal mineralocorticosteroid receptors (MR) in kidney and, if so, whether they mimic or antagonize aldosterone action. For this purpose, we evaluated the potency of 18VP and 18EP 1) to displace [3H]aldosterone binding in cytosolic fractions of kidney from adrenalectomized rats and 2) to interfere with aldosterone-induced stimulation of Na(+)-K(+)-ATPase in the collecting tubule of adrenalectomized rats. The properties of 18VP and 18EP were compared with those of their precursor progesterone and of the antimineralocorticosteroid spironolactone. The binding of [3H]aldosterone was restricted to cytosolic MR by presaturating glucocorticosteroid receptor with RU 38486. All compounds tested displaced [3H]aldosterone binding with the following efficiency: spironolactone greater than aldosterone greater than P greater than 18VP greater than 18EP; apparent Kd varied between 0.66 and 16.4 nM. Spironolactone, P, and 18VP antagonized aldosterone-induced stimulation of Na(+)-K(+)-ATPase in the collecting tubule, whereas 18EP mimicked the mineralocorticosteroid action. The different steroids tested altered Na(+)-K(+)-ATPase stimulation and aldosterone binding with the same order of potency.
Adenosine stimulates phosphate and glucose transport in opossum kidney epithelial cells
Authors: Coulson R. , Johnson R. A. , Olsson R. A. , Cooper D. R. , Scheinman S. J.
Published: December 2017

We have examined the effects of adenosine on sodium-coupled phosphate and glucose transport in cultured opossum kidney (OK) cells, a continuous cell line that resembles proximal tubule. Adenosine analogues R-(-)-N6-phenylisopropyladenosine (PIA) and 2',5'-dideoxy-adenosine (DDA) were employed as adenosine A1 receptor and P site-selective agonists, respectively. Sodium-dependent phosphate uptake activity (Na-Pi symport) increased by approximately 25% above both basal and parathyroid hormone (PTH)-inhibited levels in cells treated with PIA (0.1, 1 microM) but not in cells treated with DDA (100 microM). Adenosine (PIA) also stimulated sodium-coupled 3-O-methylglucose transport by approximately 40%. Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) content was inversely related to Na-Pi symport activity in cells treated with PIA and PTH. However, changes in Na-Pi symport activity did not consistently relate to changes in intracellular cAMP. Protein kinase C was activated 15 s after treatment of OK cells with 1 microM PIA. Preincubation of cells with 3 microM staurosporine attenuated the effect of 1 microM PIA on phosphate uptake. These data suggest that Na-Pi and Na-glucose symport activities are stimulated by adenosine acting at a receptor coupled to more than one intracellular signal. It is likely that both protein kinases A and C are involved in these actions of adenosine.
Clonidine and PGE2 have different effects on Na+ and water transport in rat and rabbit CCD
Authors: Chen L. , Reif M. C. , Schafer J. A.
Published: December 2017

We examined the effects of prostaglandin E2 (PGE2) and the adrenergic agonist clonidine on osmotic water permeability (Pf), lumen-to-bath 22Na+ flux (Jl----b), and transepithelial voltage (VT) in isolated perfused cortical collecting ducts (CCD) from rats and rabbits. Although PGE2 inhibited arginine vasopressin (AVP)-dependent Jl----b and Pf in CCDs from deoxycorticosterone (DOC)-treated and untreated rabbits, 0.1-10 microM PGE2 had no inhibitory effect on any of these transport parameters in CCDs from DOC-treated rats in presence of AVP. On the other hand, clonidine (1 microM in bathing solution) reversibly inhibited AVP-dependent Pf, Jl----b, and VT in the rat CCD by 30-40%, and 0.3 microM yohimbine, a specific alpha 2-adrenoceptor antagonist, reversed these effects. However, we were unable to demonstrate any inhibitory effect of 1-10 microM clonidine on Pf, Jl----b, or VT in the rabbit CCD using a variety of protocols. These results are consistent with the pattern of inhibition of AVP-dependent adenosine 3',5'-cyclic monophosphate (cAMP) production in the rat and rabbit CCD in that PGE2 inhibits both transport and cAMP production in the rabbit but not the rat CCD, and clonidine inhibits both transport and cAMP production in the rat but not the rabbit CCD [D. Chabardes, C. Brick-Ghannam, M. Montegut, and S. Siaume-Perez, Am. J. Physiol. 255 (Renal Fluid Electrolyte Physiol. 24): F43–;F48, 1988].
Photon-counting microcolorimeter with 40-nl cuvette
Authors: Pallone T. L.
Published: December 2017

A colorimeter with a 40-nl cuvette has been constructed. The wall of standard capillary glass was perforated to produce a sample injection port. A section of the capillary glass was drawn to a length of 1/2 cm and 80 microns ID by heating on a microforge. This produced a cuvette volume of approximately 40 nl. Two fiber-optic filaments, 80 microns in diameter, were fixed into the cuvette to transmit and receive light from the sample. The output of the colorimeter was measured with a microscope photon-counting detection assembly. It has been shown that the colorimeter enables a reduction of the plasma volume requirements of the Lowry microprotein assay from several nanoliters to 60 pl. The linearity and reproducibility of the microcolorimeter when used with the Lowry assay has been verified. The colorimeter output is several orders of magnitude above the lower limit of detection of the photon counter.
Vasoconstrictor effect of angiotensin and vasopressin in isolated rabbit afferent arterioles
Authors: Weihprecht H. , Lorenz J. N. , Briggs J. P. , Schnermann J.
Published: December 2017

The present studies were performed to examine the vasoconstrictor effect of angiotensin II (ANG II), angiotensin III (ANG III), and vasopressin in isolated afferent arterioles of the rabbit kidney. Afferent arterioles were dissected together with their glomerulus and perfused with a pressure head of 120 cmH2O. Changes in vasomotor tone were assessed as diameter changes on videotaped recordings. Afferent arterioles responded to the angiotensins and vasopressin with dose-dependent reductions in vascular diameters with half-maximum responses being observed at concentrations between 10(-9) and 10(-8) M. Responses to ANG II and III were inhibited by saralasin. Contractile responses to ANG II and vasopressin were not altered by prior occlusion of the efferent arteriole, suggesting that afferent vasoconstriction does not represent a myogenic reaction to an increase in efferent resistance. The vasoconstrictor response to ANG II was largely eliminated by removal of the glomerulus and the distal-most portion of the afferent arteriole, whereas the response to vasopressin remained intact. Our data are consistent with the notion that the juxtaglomerular apparatus (JGA) and/or glomerulus may control proximal afferent arteriolar contractility by electrotonic or myogenic coupling mechanisms or by producing cofactors that modulate vasomotor responses.
Augmented bidirectional HCO3 transport by rat distal tubules in chronic alkalosis
Authors: Wesson D. E. , Dolson G. M.
Published: December 2017

Free-flow micropuncture studies show both augmented net HCO3 reabsorption in the distal tubule of rats with chronic metabolic alkalosis and higher HCO3 delivery to this nephron segment. The present studies in rats used in vivo microperfusion of surface distal tubules to investigate whether the augmented net reabsorption 1) was due to decreased HCO3 secretion and/or to increased proton secretion or 2) depended on the higher HCO3 delivery to the distal tubule. Artificial perfusates were designed to simulate in situ deliveries of HCO3 to the distal tubules of both alkalotic and control animals and to represent extremes of in situ Cl deliveries. Rather than being decreased, both measured and calculated HCO3 secretion were higher in the alkalotic animals for each perfusate used. Similarly, calculated proton secretion (difference between net HCO3 reabsorption and calculated HCO3 secretion) was higher for the alkalotic animals using each HCO3-containing perfusate. Augmented net HCO3 reabsorption by alkalotic animals was more clearly demonstrated using higher HCO3 deliveries and Cl-free perfusates. These studies demonstrate that both the reabsorptive and secretory components of net HCO3 transport are increased in the distal tubule of animals with chronic metabolic alkalosis.