bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of vasopressin on sodium transport across inner medullary collecting duct
Authors: Kudo L. H. , van Baak A. A. , Rocha A. S.
Published: December 2017

We have used rat inner medullary collecting ducts (IMCD) perfused "in vitro" to study the effect of vasopressin (VP) on the unidirectional Na+ flux (in nmol.cm-2.s-1). We found that, at a high perfusion rate in the basal state, 24Na lumen-to-bath flux (Jl----b) was greater than the bath-to-lumen flux (Jb----l) (4.88 +/- 0.15 vs. 2.57 +/- 0.21), resulting in a significant net flux (Jnet) (P less than 0.001). Addition of 10 microU/ml of lysine vasopressin (LVP) to the bath produced a stable increase in Jl----b to 6.66 +/- 0.35 (P less than 0.001) without significant effect on Jb----l. Measuring directly the net flux absorption at lower perfusion rate (8 nl/min), we observed that LVP (10 microU/ml) produced a reversible stimulation on Jnet from 1.39 +/- 0.14 to 2.79 +/- 0.23 (P less than 0.01). The transtubular potential difference (PD) measured in the middle and final third of IMCD showed a small but significant PD (0.30 +/- 0.02 mV lumen positive) that increased significantly to 0.60 +/- 0.04 mV in the presence of LVP. However, dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP, 10(-4) M) added to the bath fluid did not change the JNa+l----b, nor was 1-desamino-8-D-arginine vasopressin (50 microU/ml), a specific V2-agonist, able to increase the Na+. We also demonstrated that JNa+l----b stimulated by LVP from 4.70 +/- 0.08 to 6.33 +/- 0.26 (P less than 0.01) was completely and reversibly inhibited by V1-antagonist, d(CH2)Tyr(Me)AVP, to 4.79 +/- 0.05. On the other hand, the absence of Ca2+ in the bath or the addition of amiloride to the lumen fluid or ouabain to the bath fluid completely inhibited AVP-stimulated JNa+l----b. Therefore, AVP and LVP increase Na+ absorption in the rat IMCD by increasing the Na+ outflux, probably generated by an increase of luminal membrane Na+ permeability modulated by extracellular Ca2+ and mediated through V1-receptors and independent of cAMP cascade.
Intrarenal metabolism of angiotensin II
Authors: Reams G. , Villarreal D. , Bauer J. H.
Published: December 2017

This study investigated the intrarenal metabolism of circulating angiotensin II. Mean arterial pressure (MAP), renal hemodynamics, and the arterial, renal venous, and renal tissue concentrations of the angiotensin octapeptide [ANG-(1–8)] were examined following the constant intra-arterial infusion of tritiated angiotensin II [( 3H]ANG-(1–8)] in graded doses of 0.5, 2.0, and 2.5 ng.kg-1.min-1 in five uninephrectomized, anesthetized female dogs. The infusion of [3H]ANG-(1–8) had no significant effect on MAP, glomerular filtration rate, renal blood flow, or urine flow rate. The mean degradation rate of intra-arterially infused [3H]ANG-(1–8) was 72%. The net renal venous plasma concentration of ANG-(1–8) was greater than that predicted from the degradation rate of [3H]ANG-(1–8). High concentrations of ANG-(1–8) were measurable in all renal tissues. However, [3H]ANG-(1–8) was not detectable in any renal tissue. These observations suggest that ANG-(1–8) in the renal venous effluent was derived, in part, de novo from intrarenal generation. Likewise, renal tissue ANG-(1–8) was derived de novo from intrarenal generation.
Distal perfusion studies: transport stimulation by native tubule fluid
Authors: Malnic G. , Berliner R. W. , Giebisch G.
Published: December 2017

It is well established that potassium secretion into the distal tubule increases with the rate of flow. In a previous study [G. Malnic, R. W. Berliner, and G. Giebisch. Am. J. Physiol. 256 (Renal Fluid Electrolyte Physiol. 25): F932-F1271, 1989] we found that the increase with the rate of perfusion with a fluid made up to resemble that normally found in the early distal tubule was substantially less than the increase in free-flow conditions [R. N. Khuri, M. Wiederholt, N. Strieder, and G. Giebisch. Am. J. Physiol. 228: 1249–1261, 1975]. Because of the possibility that some important component was missing from the artificial fluid, we have carried out another series of experiments in which distal tubules were perfused with fluid collected from late proximal tubules and compared the results with those obtained when tubules were perfused with an artificial fluid with an electrolyte composition similar to that of late proximal fluid. When proximal tubule fluid was used, the potassium concentrations in the collected distal fluid were higher and better maintained with increasing flow than when the artificial fluid was used, and consequently the rate of potassium secretion was substantially greater with the proximal tubule fluid, approaching the results of previous studies in free flow. The nature of the component missing from the artificial solution is not known.
Differential effects of respiratory inhibitors on glycolysis in proximal tubules
Authors: Dickman K. G. , Mandel L. J.
Published: December 2017

The effects of inhibition of mitochondrial energy production at various points along the respiratory chain on glycolytic lactate production and transport function were examined in a suspension of purified rabbit renal proximal tubules. Paradoxically, partial blockage at site 3 by hypoxia (1% O2) induced lactate production, whereas total site 3 blockage by anoxia (0% O2) failed to stimulate glycolysis. Compared with anoxia, hypoxic tubules exhibited greater preservation of ATP and K+ contents during O2 deprivation and more fully recovered oxidative metabolism and transport function during reoxygenation. The mitochondrial site 1 inhibitor rotenone and the uncoupler carbonyl cyanide-p-trifluorome-thoxyphenylhydrazone (FCCP) were equipotent stimuli for lactate production, whereas the site 2 inhibitor antimycin A failed to stimulate glycolysis despite a 90% inhibition of O2 consumption. Compared with antimycin A, treatment with rotenone or FCCP resulted in less cell injury [measured by lactate dehydrogenase (LDH) release] and greater preservation of cell K+ and ATP contents. 2-Deoxyglucose blocked lactate production by 50% in the presence of rotenone and increased LDH release, suggesting that glycolytic ATP is partially protective. Addition of ouabain during rotenone treatment reduced lactate production by 50%, indicating that glycolytic ATP can be used to fuel the Na pump when mitochondrial ATP production is inhibited. We conclude that 1) proximal tubules can generate lactate during inhibition of oxidative metabolism by hypoxia, rotenone, or FCCP; 2) mitochondrial inhibition is not obligatorily linked to activation of glycolysis, since neither anoxia nor antimycin A stimulate lactate production; 3) when ATP can be produced through anaerobic glycolysis it serves to protect cell viability and transport function during respiratory inhibition.
Modulation of vasopressin antidiuretic action by renal alpha 2-adrenoceptors
Authors: Gellai M.
Published: December 2017

It has been almost 40 years since the diuretic effect of alpha-adrenoceptor agonists was first demonstrated. Two possible mechanisms were proposed: inhibition of vasopressin secretion and antagonism of the cellular hydrosmotic actions of vasopressin. The debate could not be settled then for the lack of appropriate experimental models and pharmacological tools. Advances made in adrenoceptor pharmacology in the 1970s such as 1) subdivision of alpha-adrenoceptors into alpha 1- and alpha 2-subtypes; 2) development of selective agonists and antagonists; and 3) localization of both adrenoceptor subtypes in the kidney, including the proximal and collecting tubules, stimulated new research. With regard to renal adrenoceptors, selective alpha 2-agonists have been shown to induce diuresis in dogs and rats. Whereas in the dog the increase in urine flow results mostly from an increase in osmolal clearance, in the rat the diuresis results in large part from an increase in the excretion of solute-free water. In vitro studies on isolated collecting tubules from rats and rabbits (none from dogs) have shown that alpha 2-agonists inhibit vasopressin-induced adenosine 3',5'-cyclic monophosphate formation and that this effect is mediated by the inhibitory guanine nucleotide regulatory protein and abolished by pertussis toxin treatment. In vivo evidence in support of such a mechanism was presented from conscious Brattleboro homozygous rats in which a selective alpha 2-agonist inhibited the antidiuretic effect of exogenous vasopressin, and this effect was abolished by pertussis toxin. The physiological importance of renal alpha 2-adrenoceptors was identified by use of adrenal medullectomized rats and the alpha 2-antagonist, yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)
Autoradiographic localization of atrial natriuretic peptide receptor subtypes in rat kidney
Authors: Brown J. , Salas S. P. , Singleton A. , Polak J. M. , Dollery C. T.
Published: December 2017

The distribution of atrial natriuretic peptide (ANP) clearance receptors in rat kidney was investigated by in vitro autoradiography using des[Gln18,Ser19,Gly20,Leu21,Gly22]-ANP-(4- 23) (C-ANP) and 125I-Tyr0-ANP-(5-25) as relatively specific ligands of this receptor. Alpha-125I-ANP (100 pM) bound reversibly but with high affinity to glomeruli, outer medullary vasa recta bundles, and inner medulla. C-ANP (10 microM) inhibited greater than 60% of this glomerular binding but did not inhibit the binding of alpha-125I-ANP to medullary tissues. Alpha-125I-ANP also bound reversibly to the renal arteries up to the glomerulus. This arterial binding was only partly inhibited by 10 microM C-ANP. In the presence of 10 microM C-ANP, increasing concentrations of alpha-125I-ANP bound to a residue of glomerular sites with apparent dissociation constants of 0.82 +/- 0.16 to 2.73 +/- 1.20 nM at different cortical levels. 125I-Tyr0-ANP-(5-25) bound significantly to glomeruli and intrarenal arteries but not to vasa recta bundles or inner medulla. This glomerular binding also occurred with nanomolar dissociation constants. It was completely inhibited by 1 microM alpha-ANP and 10 microM C-ANP, but not by unrelated peptides such as gastrin. These results suggest that renal ANP clearance receptors are restricted in vivo to the glomeruli and renal arterial system of the rat.
TGF-initiated vascular interactions between adjacent nephrons in the rat kidney
Authors: Kallskog O. , Marsh D. J.
Published: December 2017

We sought to determine whether tubuloglomerular feedback (TGF), activated from one nephron, affects other arterioles derived from the same cortical radial artery. Surface nephrons supplied by a single cortical radial artery were identified by injecting Ringer solution containing Fast Green from a narrow-gauge polyethylene catheter inserted via a lumbar artery into a renal artery. Stop-flow pressure was measured in an identified nephron from such a grouping. In one series, increasing end-proximal flow rate from 0 to 50 nl/min of synthetic tubular fluid in one member of an identified pair of nephrons reduced stop-flow pressure by 1.3 +/- 0.2 mmHg in the other member. When the nephrons were derived from different cortical radial arteries, the stop-flow pressure changed -0.2 +/- 0.1 mmHg. In another series, increasing flow in the adjacent nephron from 0 to 50 nl/min decreased stop-flow pressure 3.9 +/- 0.9 mmHg, and increasing flow in the adjacent nephron by the same amount when flow in the first nephron was 50 nl/min decreased stop-flow pressure 3.4 +/- 0.7 mmHg. These results indicate the operation of an interaction among nephrons derived from a common cortical radial artery. Such an interaction could produce a cooperative effect larger than that predicted from measured single-nephron responses when systemic arterial pressure changes.
Mechanisms of perfused kidney cytoprotection by alanine and glycine
Authors: Baines A. D. , Shaikh N. , Ho P.
Published: December 2017

We examined the cytoprotective action of individual amino acids in isolated perfused kidneys during perfusion with either 10 mM lactate or 5 mM glucose. In the absence of amino acids inulin clearance fell rapidly, whereas fractional excretion of phosphate, lactate, or glucose increased to more than 30%; lactate dehydrogenase was released into perfusate and alkaline phosphatase into the urine. Functional deterioration was less in kidneys from rats rendered chronically water diuretic by drinking 5% glucose. Adding 5 mM glycine, L-alanine, beta-alanine, or D-alanine to the perfusate also prevented functional deterioration and release of enzymes. Glycine perfusion increased total phospholipid per microgram DNA by 6%. Aspartate, glutamate, glutamine, taurine, isoleucine, leucine, and valine were not protective. Serine, proline, and alpha-aminoisobutyric acid had small protective effects. Micropuncture measurements of proximal tubular free- and stop-flow pressures showed no effect of L-alanine on glomerular hemodynamics. L-Alanine increased oxygen consumption by both glucose- and lactate-perfused kidneys and increased gluconeogenesis by lactate-perfused kidneys but did not alter renal ATP content or energy charge. L-Alanine was not consumed during 70 min of perfusion and its protective action was not inhibited by blocking transamination with 0.5 mM amino-oxyacetate. The protective action of glycine was not inhibited by blocking glycine metabolism with 0.1 mM cysteamine. Thus the beneficial effects of L-alanine and glycine do not require their metabolism. These observations suggest that small neutral amino acids prevent tubular disruption through their physicochemical effects, which can stabilize membrane protein tertiary structure.
Endothelium-derived relaxing factor influences renal vascular resistance
Authors: Radermacher J. , Forstermann U. , Frolich J. C.
Published: December 2017

The mechanism of action of different vasodilators was investigated in the isolated perfused kidney of the rat. Acetylcholine (ACh, 10 nM-1 microM) and ATP (10 nM-1 microM), compounds known to relax isolated arteries in an endothelium-dependent fashion, caused concentration-dependent decreases in renal vascular resistance (RVR). Also, the endothelium-independent vasodilators verapamil (100 nM-10 microM), glyceryl trinitrate (GTN, 1-100 microM), and sodium nitroprusside (SNP, 1-100 microM) reduced RVR concentration dependently. Gossypol (10 microM, 5 min), an inhibitor of endothelium-derived relaxing factor (EDRF) production and/or release, increased basal RVR by 5% and significantly inhibited the vasodilator effects of ACh and ATP but had no effect on verapamil- or GTN-induced decreases in RVR. Methylene blue (MB) increased RVR dose dependently by up to 50%. About 50% of this effect could be antagonized with phentolamine (1 microM). MB abolished the relaxant response to ATP and attenuated the response to ACh. The dose-response curve of SNP was shifted to the right, and the relaxation to verapamil was slightly reduced. L-NG-methylarginine (100 microM) increased RVR by approximately 20%, and this effect was completely reversed by L-arginine (1 mM). N omega-nitro-L-arginine (100 microM) increased RVR by approximately 40% and attenuated the response to ATP but had no effect on the SNP-induced decrease in RVR. These results suggest that EDRF plays an important role in the regulation of RVR.
Effect of high extracellular K+ on Na-K-ATPase in cultured canine kidney cells
Authors: Manuli M. A. , Edelman I. S.
Published: December 2017

The Madin-Darby canine kidney (MDCK) cell line was used to evaluate the influence of high extracellular K+, independent of hormonal effects, on renal Na-K-adenosinetriphosphatase (ATPase) activity and abundance. Confluent cell monolayers were incubated in control (5 mM) or high K+ (7.5 mM) medium for 24 h. Exposure to high K+ elicited a 46% rise in Na-K-ATPase activity and a 55% increase in ouabain-sensitive 86Rb uptake. Na-K-ATPase abundance, estimated from the number of ouabain-binding sites, also increased 63% over control in cells exposed to 7.5 mM K+, and as a consequence there was no statistically significant change in the catalytic turnover number. Northern blot analysis using rat cDNA probes for the alpha 1- and beta-subunits showed no corresponding changes in subunit-specific mRNA abundances at 24 h. We conclude that chronic exposure to high extracellular K+ produces a rise in renal epithelial Na-K-ATPase activity and active K+ transport, independent of changes in aldosterone, renal blood flow, or extracellular Na+ concentration. This effect is due to an increase in enzyme abundance rather than a change in catalytic turnover rate. The results of Northern analysis suggest that regulation of Na-K-ATPase activity and abundance by high K+ may involve translational or posttranslational mechanisms, but further study with cDNA probes of canine origin is needed to resolve this issue.
Difference in the Na affinity of Na(+)-K(+)-ATPase along the rabbit nephron: modulation by K
Authors: Barlet-Bas C. , Cheval L. , Khadouri C. , Marsy S. , Doucet A.
Published: December 2017

The sensitivity of Na(+)-K(+)-ATPase to Na was determined in single segments of rabbit nephron isolated by microdissection. In the cortical collecting tubule (CCT), Na(+)-K(+)-ATPase was threefold more sensitive to Na (apparent K0.5 approximately 3 mM) than in proximal convoluted tubule and cortical thick ascending limb (apparent K0.5 approximately 10 mM). Furthermore, increasing K concentration from 5 to greater than 100 mM markedly reduced the affinity of the pump for Na in all three nephron segments. In fact, the main shift in Na affinity occurred when K changed from 100 to 120 mM; in the CCT, increasing K concentration from 100 to 120 mM while maintaining Na concentration at 10 mM reduced Na(+)-K(+)-ATPase activity by greater than 35%. These findings confirm that, in kidney cells as in other cells, intracellular Na limits the rate of Na(+)-K(+)-ATPase. Thus any alteration of intracellular Na concentration modifies the pump activity in a way that contributes to the restoration of intracellular Na homeostasis. This adaptive property is particularly efficient in the collecting tubule in which the apparent K0.5 of the pump for Na is close to normal intracellular Na concentration. Furthermore, changes in intracellular K concentration, which usually accompany those of Na so as to maintain the total cation concentration constant, potentiate the regulatory role of Na through modifications of its affinity for the pump.
Cyclooxygenase inhibition enhances rat interleukin 1 beta-induced growth of rat mesangial cells in culture
Authors: Stahl R. A. , Thaiss F. , Haberstroh U. , Kahf S. , Shaw A. , Schoeppe W.
Published: December 2017

The cytokine interleukin 1 (IL-1) has growth-promoting activities on mesangial cells (MC) and enhances MC prostanoid formation. A possible role of endogenous cyclooxygenase products on IL-1-mediated growth of MC is, however, unknown. Therefore we evaluated the effect of cyclooxygenase inhibition on growth of mesangial cells in culture, which were exposed to DNA recombinant rat interleukin 1 beta (rIL-1 beta). rIL-1 beta increased [3H]thymidine uptake in MC by approximately 70% after 48 h. This growth-promoting activity of the cytokine was observed at 1 ng/ml and was not further enhanced by the increase of the IL-1 beta concentration less than or equal to 100-fold. IL-1 beta, however, dose dependently stimulated prostaglandin E2 (PGE2) formation by MC. When prostaglandin synthesis was inhibited by indomethacin (Indo, 1 microgram/ml), rIL-1 beta (10 ng/ml)-induced cell proliferation was sevenfold greater compared with rIL-1 beta alone. In the presence of Indo (1 microgram/ml), rIL-1 beta (1, 10, 50, and 100 ng/ml) dose dependently stimulated MC proliferation. The addition of exogenous PGE2 (10(-7) and 10(-8) M) to Indo-treated MC blocked the mitogenic response of IL-1 beta. We conclude that endogenous PGE2 formation, which is stimulated by IL-1 beta, antagonizes the growth-promoting activity of the cytokine. PGE2 may thus exert antiproliferative effects in glomerular diseases, whereas IL-1 might mediate cell growth.
Downregulation of parathyroid hormone receptors in renal membranes from aged rats
Authors: Hanai H. , Brennan D. P. , Cheng L. , Goldman M. E. , Chorev M. , Levine M. A. , Sacktor B. , Liang C. T.
Published: December 2017

The mechanism of the inhibition or blunting of parathyroid hormone (PTH)-stimulated Na(+)-Ca2+ exchange activity in renal cortical cells from aged rats was examined. The number of PTH binding sites in basolateral membranes prepared from adult (6 mo) and old (24 mo) rats was quantitated by the binding of the synthetic analogue 125I-labeled [Nle8,18, Tyr34]bPTH-(1-34) amide to the membrane. The maximum number of specific PTH binding sites, Bmax, was 92.7 +/- 9.3 and 36.7 +/- 6.1 fmol/mg protein, respectively, in membranes prepared from adult and old rats. The affinity of the receptor to PTH was unaffected with age. The level of PTH binding components (68 and 70 kDa) estimated by a ligand affinity blot technique using biotinylated bPTH-(1-34) as the ligand was similarly reduced in membranes isolated from senescent rats. To test the hypothesis that change in the number of PTH binding sites and level of PTH binding components represented an adaptive response to a high serum PTH level, rats were parathyroidectomized (PTX) and the changes were reexamined. Decreases in the number of PTH binding sites and PTH binding components were either partially or completely negated by the surgery. These findings suggest that the blunting of both the PTH-stimulated Na(+)-Ca2+ exchange and adenylate cyclase activities in the kidneys of aged rats was due, in part, to be loss of PTH receptors in basolateral membranes and that this defect could be partially reversed by removal of the parathyroid gland.
Stimulation of transient elevations in cytosolic Ca2+ is related to inhibition of Pi transport in OK cells
Authors: Miyauchi A. , Dobre V. , Rickmeyer M. , Cole J. , Forte L. , Hruska K. A.
Published: December 2017

Stimulation of changes in cytosolic free calcium by parathyroid hormone was determined in three opossum kidney (OK) cell types, OK wild-type, OKP clone, and OKH clone. All three types of OK cells express parathyroid hormone (PTH)-sensitive adenylate cyclase and adenosine 3',5'-cyclic monophosphate (cAMP) production. However, only the OK wild-type and the OKP clone respond to PTH with inhibition of sodium-dependent Pi transport and transient increase in cytosolic calcium. Characterization of the increases in cytosolic calcium in the wild-type and OKP clones revealed they were due in part to stimulation of Ca2+ release from intracellular stores, probably by inositol 1,4,5-trisphosphate (IP3), which was stimulated by PTH. PTH-stimulated Ca2+ transients were also inhibited by protein kinase C activation. These data are compatible with PTH receptor-mediated phospholipase C activation and its feedback inhibition by protein kinase C. The OKH cells demonstrated a slow increase in cytosolic calcium when stimulated by cyclic nucleotides but no evidence for PTH stimulation of Ca2+ release from intracellular stores. Thus the absence of an inhibitory response of sodium-dependent Pi transport to PTH in the OKH cells is associated with the absence of the rapid transient elevations of cytosolic Ca2+ such as those produced by IP3 production. These data suggest an important cooperative role for cAMP and the phospholipase C-stimulated Ca2(+)-protein kinase C message system in the regulation of Pi transport.
Salicylic acid permeability properties of the rabbit cortical collecting duct
Authors: Chatton J. Y. , Besseghir K. , Roch-Ramel F.
Published: December 2017

To assess the role of nonionic diffusion of salicylic acid (pKa = 3) in the terminal nephron, we measured the passive permeability of [14C]salicylic acid in rabbit cortical collecting ducts isolated and perfused in vitro. This segment can produce and maintain a maximal pH gradient between blood and tubular fluid. When peritubular pH was kept constant at pH 7.4 the apparent permeability of salicylic acid (P', 10(-6) cm/s) was 6.2 +/- 1.1 at a luminal pH of 6.0, 17.2 +/- 5.3 at a luminal pH of 5.5, and 39.0 +/- 4.7 at a luminal pH of 5.0. These permeabilities were in close correlation with the percentage of nonionized salicylic acid present at each pH, indicating that only the nonionized molecule can diffuse across the collecting duct epithelium. By recalculating the permeability, taking into account only the concentration of the nonionized salicylic acid molecules, we obtained the apparent permeability of nonionized salicylic acid, which was no longer pH dependent and averaged 4,345 +/- 460 x 10(-6) cm/s. The apparent activation energy of this diffusion process was 9.3 +/- 1.2 kcal/mol as calculated from an Arrhenius plot.
Evidence that dopamine-2 mechanisms control renal function
Authors: Siragy H. M. , Felder R. A. , Howell N. L. , Chevalier R. L. , Peach M. J. , Carey R. M.
Published: December 2017

Dopamine is synthesized by the kidney, and dopamine-2 (DA2) receptors are present in the renal glomerulus. However, no role for DA2 receptors in the kidney has been defined. We investigated the possible role of DA2 receptors in control of renal function by intrarenal infusion of a highly specific DA2 antagonist YM-09151 (YM), in conscious uninephrectomized dogs (n = 5) in metabolic balance at Na intake 40 meq/day. YM infused at 0.01 pmol.kg-1.min-1 did not cause any changes in urinary flow rate or Na excretion. Administration of YM (infusions from 0.1 to 10.0 pmol.kg-1.min-1) caused a significant dose-dependent diuresis (F = 20.3; P less than 0.001) and natriuresis (F = 35.2; P less than 0.0001) and an increase in glomerular filtration rate (F = 45.4; P less than 0.0001), renal plasma flow (F = 209.3; P less than 0.0001), and filtration fraction (F = 11.2; P less than 0.0001). No significant changes in plasma renin activity, plasma aldosterone concentration, or mean arterial blood pressure occurred with any of the doses of YM infused into the renal artery. Coinfusion of LY-171555, a specific DA2 agonist, at a dose that itself did not affect renal function, completely abrogated the renal hemodynamic and excretory changes induced by YM. The data suggest that dopamine produced intrarenally may act at renal vascular and/or glomerular DA2 receptors to control renal function.
Identification of a putative Na(+)-H+ exchanger regulatory cofactor in rabbit renal BBM
Authors: Morell G. , Steplock D. , Shenolikar S. , Weinman E. J.
Published: December 2017

Previous in vitro studies with detergent-solubilized rabbit renal brush-border membrane (BBM) proteins have suggested that adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA)-mediated inhibition of the Na(+)-H+ exchanger requires the presence of 42-kDa cofactor that is distinct from the exchanger itself. We sought to determine whether there was a protein in native rabbit renal BBM vesicles that has characteristics similar to that of the 42-kDa cofactor. Incubation of native BBM vesicle proteins with a hypotonic phosphorylation solution containing purified catalytic subunit of PKA resulted in phosphorylation of a number of BBM proteins, including a protein with an apparent molecular weight that was similar but not identical to that of the 42-kDa cofactor obtained from anion-exchange column chromatography of n-octyl glucoside-extracted BBM proteins. The identity between the BBM vesicle protein and the 42-kDa cofactor was established by phosphopeptide maps and radioiodinated peptide maps. These results indicate that native BBM vesicles contain a number of proteins that are phosphorylated by PKA when the PKA and ATP are present inside the vesicle space. One of these proteins appears to be identical to the 42-kDa protein that, as previously suggested by in vitro studies, acts as a regulatory cofactor mediating the inhibitory effect of PKA on the renal Na(+)-H+ exchanger.
Localization of arginine synthesis along rat nephron
Authors: Levillain O. , Hus-Citharel A. , Morel F. , Bankir L.
Published: December 2017

Arginine production was measured in isolated rat nephron segments. Segments were incubated with 0.3 mM aspartate and 0.1 mM L-[ureido-14C]-citrulline in a sealed chamber. Arginase and urease were added to the medium to hydrolyze arginine and to release 14CO2, which was trapped in KOH and counted. Arginine synthesis was found only in the proximal tubule, with decreasing intensity from proximal convoluted (PCT) to proximal straight tubule (PST). Results were as follows (in fmol.min-1.mm tubule length-1): PCT, 122 +/- 15; cortical PST, 71 +/- 6; outer medullary PST, 41 +/- 4; all other segments, less than 6. Arginine synthesis changed almost proportionally with precursor concentration of less than or equal to 0.4 mM. We had shown previously that PST but not PCT was able to hydrolyze arginine into urea and ornithine. In this study arginine was further hydrolyzed in cortical (40%) and medullary (64%) PST but not in PCT. These observations suggest that the arginine formed in PCT contributes to the maintenance of the whole body arginine pool, whereas most of the arginine formed in PST might contribute, by its conversion to urea, to the process of urine concentration.
Effects of atrial natriuretic peptide on renal arterioles: morphometric analysis using microvascular casts
Authors: Kimura K. , Hirata Y. , Nanba S. , Tojo A. , Matsuoka H. , Sugimoto T.
Published: December 2017

In normal rat kidneys, the effect of atrial natriuretic peptide (ANP) on the diameter of the arterioles was evaluated by scanning electron microscopy of vascular casts. Acryl resin was infused into rat kidneys during the administration of ANP, either alone or with norepinephrine (NE). ANP infusion constricted the proximal efferent arteriole in the superficial cortex. Although NE constricted the proximal and distal segments of the afferent arteriole in the superficial cortex, the addition of ANP reversed the constriction and further constricted the efferent arteriole. In the deep cortex, only the proximal segment of the afferent arteriole was dilated by ANP when infused with NE. In a separate set of experiments, ANP increased both the glomerular filtration rate (GFR) and urinary sodium excretion (UNaV), and NE decreased the renal blood flow (RBF). However, administration of ANP after NE recovered RBF and increased GFR as well as UNaV. Results indicate that ANP increases GFR and natriuresis by constricting the efferent arteriole. NE appears to decrease RBF by constricting the afferent arteriole. ANP antagonizes the renal effects of NE primarily by dilating afferent arterioles.
PKC and Pi deprivation modulate differently the ubiquitous Na-dependent Pi uptake in MDCK cells
Authors: Escoubet B. , Garestier M. C. , Cherqui G. , Amiel C.
Published: December 2017

The role of protein kinase C (PKC) in the modulation of the ubiquitous sodium-dependent phosphate transport and in adaptation of that transport to phosphate deprivation was investigated in MDCK cells. Phorbol myristate acetate (PMA) had a biphasic effect on sodium-dependent phosphate uptake characterized by early inhibition (-25% at 1 h) followed by late stimulation (2.3-fold at 15 h). Late stimulation was related to a decreased apparent affinity (Km) with unchanged maximal velocity (Vmax). The 15-h stimulation of phosphate uptake was also induced by an initial 1-h PMA treatment followed by a 14-h washout of PMA or by R59 022. The stimulation was inhibited by PKC downregulation. PMA stimulation was dependent on protein synthesis but not on transcription, as shown by the respective effects of cycloheximide, 3'-deoxyadenosine, and actinomycin D. In phosphate-deprived cells PMA had also a biphasic effect. A potentiation of PMA stimulation of phosphate uptake with phosphate deprivation was observed. Adaptation to phosphate deprivation was not prevented by PKC downregulation. Cytosolic and membranous PKC activities were not changed by 15-h phosphate deprivation. We conclude that 1) PKC modulates sodium-dependent phosphate uptake in MDCK cells, and 2) phosphate deprivation and PKC modulation of sodium-dependent phosphate uptake involve different cellular pathways; that is, phosphate deprivation acts through gene regulation, and PKC acts through translation regulation.
Pathophysiology of vascular smooth muscle in renin promoter-T-antigen transgenic mice
Authors: Sigmund C. D. , Jones C. A. , Jacob H. J. , Ingelfinger J. , Kim U. , Gamble D. , Dzau V. J. , Gross K. W.
Published: December 2017

The pathophysiological consequence of targeted production of SV-40 T-antigen to renin-expressing cells in the kidney of transgenic mice is reported. A histopathologic analysis of the kidney from adult transgenic mice (12–16 wk old) revealed the presence of severe vascular lesions manifested by marked atypical hyperplasia of vascular smooth muscle. The levels of plasma renin, kidney renin, and kidney renin mRNA were examined in 6- and 9-wk-old transgenic mice and were found to be significantly lower than their age-matched non-transgenic littermates and were nonresponsive to captopril treatment. However, there was no significant difference in conscious mean arterial pressure between transgenic and non-transgenic mice. The levels of renal renin mRNA in transgenics and nontransgenic littermates were compared throughout ontogeny and were found to be equal in newborns, elevated 3- to 5-fold in 1-wk-old transgenics, and yet decreased 10-fold by 6 wk of age in transgenic mice. Expression of the transgene in the kidney exhibited the proper developmental pattern and was properly restricted to juxtaglomerular cells in neonatal mice. Nevertheless, in adult mice, T-antigen-containing cells were found throughout the entire renal arterial tree. The observed ability of renal vascular cells to be recruited to express both renin and T-antigen suggests a mechanism that can explain the development of the renal pathology in these mice.
Sodium transport in salamander proximal tubule at 5.5 degrees C
Authors: Morgunov N. S. , Hirsch D. J.
Published: December 2017

Na+ transport and electrophysiology of isolated perfused proximal tubules of the salamander Ambystoma tigrinum were compared at 22 and 5.5 degrees C, a range over which these animals normally live. Both intracellular Na+ activity and basolateral membrane potential were unaffected by temperature, whereas transepithelial potential depolarized from -6.5 +/- 0.8 mV at 22 degrees C to -3.5 +/- 0.6 mV at 5.5 degrees C (P less than 0.05). Compared with 22 degrees C, reduction of temperature to 5.5 degrees C included major increases in apical membrane resistance (2,052 +/- 473 omega.cm2 to 18,464 +/- 2,667 omega.cm2) and basolateral membrane resistance (491 +/- 113 omega.cm2 to 1,780 +/- 256 omega.cm2) (P less than 0.01). Sequential increases of luminal glucose concentration allowed characterization of the Na(+) -glucose cotransporter at both temperatures. The Km was stable (2 mM), but the maximal activity (Vmax) at 5.5 degrees C of 167 peq/5 cm2 increased to 1,000 peq/5 cm2 at 22 degrees C (P less than 0.05). In parallel with this temperature sensitivity of apical Na+ entry, basolateral Na+ pump activity was reduced at low temperature. Rubidium uptake at 22 degrees C was reduced by 40% at 5.5 degrees C. The rate of decrease of intracellular Na+ activity when tubules were perfused with substrate-free solution was -2.6 +/- 0.7 mM/min at 5.5 degrees C, compared with -4.9 +/- 1.2 mM/min at 22 degrees C. We conclude that low temperature reduces both Na+ uptake and efflux, allowing stability of intracellular milieu despite reduction in net transepithelial transport.
Charge selectivity in kidney ultrafiltration is associated with glomerular uptake of transport probes
Authors: Tay M. , Comper W. D. , Singh A. K.
Published: December 2017

The isolated perfused kidney exhibits substantial charge selectivity, as in vivo, in relation to fractional clearance of [3H]dextran sulfate and [3H]dextran. When cycloheximide is present in perfusate, fractional clearance of dextran sulfate is increased and proteinuria becomes significant, but glomerular filtration rate remains essentially unchanged compared with control. The possible role of cells in affecting transglomerular transport was demonstrated when isolated glomeruli from control perfused kidneys showed a very significant resident concentration of [3H]dextran sulfate and [3H]albumin, whereas there was no corresponding accumulation of [3H]dextran or [3H]inulin. Glomerular concentration of dextran sulfate and albumin was significantly reduced by cycloheximide. Kinetics of uptake and release of glomerular dextran sulfate indicated that it had a half-life of glomerular residence of approximately 2-3 min and that this half-life was considerably extended in the presence of cycloheximide. The half-life for glomerular residence of albumin was in the range of 30-40 min. The conclusion from this work is that glomerular charge selectivity for dextran sulfate could be quantitatively rationalized on the basis of transient uptake and release by glomerular cells.
Protein-induced modulation of renin secretion is mediated by prostaglandins
Authors: Kapoor S. C. , Krishna G. G.
Published: December 2017

Dietary protein restriction inhibits glomerular prostaglandin (PG) synthesis and lowers plasma renin activity (PRA). To investigate the role of PG in mediating protein-induced alterations in renin secretion, male Sprague-Dawley rats were fed isocaloric diets providing either a standard 20% protein or a low-protein (6%) diet for 3 wk. An additional group of rats received a PG synthesis inhibitor, meclofenamate (25 mg/l), in the drinking water along with the 20% protein diet. Both protein restriction and meclofenamate administration significantly (P less than 0.025) lowered glomerular PGE2 production. Compared with standard protein intake, low protein intake lowered basal PRA (3.96 +/- 0.16 vs. 1.58 +/- 0.12 ng.ml-1.h-1, P less than 0.001), stimulated PRA (11.6 +/- 2.3 vs. 5.5 +/- 0.7 ng.ml-1.h-1, P less than 0.025), renal venous PRA (10.0 +/- 0.7 vs. 7.02 +/- 0.72 ng.ml-1.h-1, P less than 0.02), and plasma angiotensin II (ANG II) levels (52 +/- 5 vs. 24 +/- 3 pg/ml, P less than 0.01), while augmenting renal tissue renin content (2.36 +/- 0.21 vs. 3.56 +/- 0.30 micrograms/mg protein, P less than 0.005). Changes in plasma and renal tissue renin on meclofenamate treatment were similar to those observed on 6% protein diet. Both protein restriction and meclofenamate administration increased the glomerular ANG II receptor number, while the receptor affinity was unchanged. Thus protein restriction lowers PRA by impairing release of renin into circulation. This impairment in renin release is mediated by PG.
Effect of protamine on ion conductance of upper portion of descending limb of long-looped nephron from hamsters
Authors: Koyama S. , Yoshitomi K. , Imai M.
Published: December 2017

To estimate the contribution of paracellular shunt pathway to the cation-selective permeability in the upper portion of the descending limb of long-looped nephron (LDLu) of hamsters, we observed the effect of protamine on salt-diffusion voltage (delta VT) and transmural resistance (RT). delta VT generated on reduction of lumen NaCl concentration was decreased from 12.0 +/- 1.4 to 7.3 +/- 1.2 mV when 100 micrograms/ml protamine were added to the lumen. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin reversed the delta VT toward the control level. The effect of protamine was dose dependent in the range from 3 to 1,000 micrograms/ml. Protamine was without effect from the bath. Studies on single salt dilution voltage revealed that 100 and 300 micrograms/ml protamine inhibited relative Na+ to Cl- permeability from 4.03 +/- 0.38 to 2.14 +/- 0.21 and from 3.75 +/- 0.37 to 1.36 +/- 0.09, respectively. Protamine markedly decreased the apparent transference number for Na+ but slightly increased the value for Cl-. Protamine also inhibited permeabilities for K+, Rb+, and Li+ relative to Cl-, indicating that the inhibitory effect of protamine was not confined to Na+ but was generalized to cations. Transmural cable analysis showed that 100 micrograms/ml protamine increased RT from 14.0 +/- 1.1 to 19.3 +/- 1.2 omega.cm2, with the effect being reversed by 30 U/ml heparin. Because the effect of protamine on RT was unaffected by ouabain in the bath, changes in RT may mainly represent those of the paracellular shunt resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
Kinin and tubuloglomerular feedback in normal and hydronephrotic rats
Authors: Morsing P. , Persson A. E.
Published: December 2017

The role of bradykinin in resetting the tubuloglomerular feedback (TGF) mechanism was studied with the stop-flow technique in control and hydronephrotic Inactin-anesthetized rats. Glomerular function was assessed by measuring stop-flow pressure (Psf); the maximal decrease in stop-flow pressure (delta Psf) with increased loop of Henle perfusion and the perfusion that elicited half-maximal delta Psf, the turning point (TP), were determined. Bradykinin infusion resulted in resetting of TGF in both control and hydronephrotic rats but in different directions. A decreased sensitivity was found in control rats (TP increased from 18.6 to 26.4 and 16.8 to 22.1 nl/min on systemic and intratubular administration, respectively). In hydronephrotic rats the sensitivity of TGF increased. TP decreased from 19.9 to 15.2 nl/min with bradykinin administered systemically and from 18.4 to 15.0 nl/min on intratubular administration. These results show that exogenous kinin administration mimics the effects of extracellular volume expansion on TGF resetting and demonstrate a difference in resetting in hydronephrotic and control kidneys.
Regulated expression of endothelin 1 in glomerular capillary endothelial cells
Authors: Marsden P. A. , Dorfman D. M. , Collins T. , Brenner B. M. , Orkin S. H. , Ballermann B. J.
Published: December 2017

Endothelin (ET)-1 is a powerful vasoconstrictor known to be produced and secreted by endothelial cells lining large vessels. Because ET-1 stimulates glomerular mesangial cell contraction, glomerular capillary endothelial cells (GEN), normally situated in close apposition to mesangial cells, were examined for potential ET expression and secretion. Cultured bovine GEN released ET in a time-dependent fashion. ET secretion was significantly stimulated by bradykinin, an agonist known to activate phospholipase C in these cells. Preproendothelin 1 (preproET-1) mRNA levels in GEN rose in a biphasic manner on stimulation with bradykinin. The early increments (at 30 min) were not dependent on new protein synthesis, whereas the late rise (6 h after addition of bradykinin) appeared to be protein synthesis dependent. Neither early or late bradykinin-stimulated preproET-1 mRNA expression in glomerular endothelial cells was due to inhibition of mRNA breakdown. Both phases of preproET-1 mRNA expression were observed with other glomerular endothelial cell calcium-mobilizing agonists, namely thrombin, and were mimicked by the calcium ionophore ionomycin. By contrast, the protein kinase C activator phorbol myristate acetate only enhanced preproET-1 mRNA expression at 30 min and suppressed expression thereafter. It is concluded that GEN have the potential to express and secrete ET-1 in a phospholipase C-regulated fashion. Furthermore, because glomerular mesangial cells respond to this peptide, the findings raise the possibility of paracrine regulation of mesangial cell tone by glomerular endothelial cell-derived ET-1.
Colocalization of insulin-like growth factor-binding protein with insulin-like growth factor I
Authors: Kobayashi S. , Clemmons D. R. , Venkatachalam M. A.
Published: December 2017

We report the localization of insulin-like growth factor I (IGF-I) and a 25-kDa form of insulin-like growth factor-binding protein (IGF-BP-1) in adult rat kidney. The antigens were localized using a rabbit anti-human IGF-I antibody, and a rabbit anti-human IGF-BP-1 antibody raised against human 25-kDa IGF-BP-1 purified from amniotic fluid. Immunohistochemistry by the avidin-biotin peroxidase conjugate technique showed that both peptides are located in the same nephron segments, in the same cell types. The most intense staining was in papillary collecting ducts. There was moderate staining also in cortical collecting ducts and medullary thick ascending limbs of Henle's loop. In collecting ducts the antigens were shown to be present in principal cells but not in intercalated cells. In distal convoluted tubules, cortical thick ascending limbs, and in structures presumptively identified as thin limbs of Henle's loops there was only modest staining. The macula densa, however, lacked immunoreactivity. Colocalization of IGF-I and IGF-BP-1 in the same cells supports the notion, derived from studies on cultured cells, that the actions of IGF-I may be modified by IGF-BPs that are present in the same location.
Norepinephrine spillover faithfully reflects renal sympathetic nerve activity in conscious rabbits
Authors: Noshiro T. , Saigusa T. , Way D. , Dorward P. K. , McGrath B. P.
Published: December 2017

The relationship between directly recorded renal sympathetic nerve activity (RSNA) and simultaneous renal norepinephrine (NE) spillover rate across the kidney at rest and in response to changes in mean arterial pressure (MAP) was examined in six conscious rabbits. Integrated RSNA and renal NE spillover rate at rest were 5.1 +/- 1.1 microV/s and 20.8 +/- 3.0 ng/min, respectively. Sodium nitroprusside infusions at 10 and 20 microgram.kg-1.min-1 significantly increased RSNA by 42 +/- 14 and 84 +/- 14% and renal NE spillover rate 39 +/- 22 and 107 +/- 22% in response to falls in MAP of 15 +/- 2 and 21 +/- 2 mmHg (19 and 27%), respectively. During phenylephrine infusion at 8 micrograms.kg-1.min-1, RSNA and renal NE spillover rate significantly decreased by 65 +/- 14 and 67 +/- 16%, respectively, in response to a 15 +/- 2 mmHg (19%) rise in MAP. There was a highly significant positive correlation between changes in directly recorded RSNA and changes in renal NE spillover rate (r = 0.81, P less than 0.01). The ratio of renal to total NE spillover rate at rest was 0.44 +/- 0.06. This ratio was decreased during both sympathetic stimulation (0.30 +/- 0.04) and inhibition (0.26 +/- 0.06). This study indicates that the measurement of renal NE spillover rate is a useful reliable method for detecting the changes in RSNA and its relative contribution to overall sympathetic nerve activity in response to physiological stimuli in conscious rabbits.
Pathogenesis of glomerular sclerosis in subtotally nephrectomized analbuminemic rats
Authors: Fujihara C. K. , Limongi D. M. , Falzone R. , Graudenz M. S. , Zatz R.
Published: December 2017

The Nagase analbuminemic rat (NAR), a mutant of the Sprague-Dawley (SD) strain, exhibits persistent hypercholesterolemia, thrombocytosis, and enhanced platelet aggregation, abnormalities possibly involved in the genesis of glomerular sclerosis (GS). Previous observations suggest that these rats never develop aging GS. We studied the development of GS in NAR after 5/6 nephrectomy (Nx). Fifteen days after Nx, marked glomerular hypertension was observed in NAR, compared with only mild elevations in SD rats. Glomerular hypertrophy was more marked in SD rats than in NAR. Enalapril normalized glomerular volume and partially reversed glomerular hypertension in NAR without altering platelet function or cholesterol levels. Glomerular endothelial injury and intraluminal fibrin deposition were seen only in NAR. Two months after Nx, severe GS and massive glomerular lipid deposition were seen in NAR, whereas only mild glomerular injury occurred in SD rats. Enalapril attenuated GS and prevented lipid deposition in NAR. Glomerular hypertension may be a key factor in the genesis of GS in this model in association with endothelial injury, intracapillary coagulation, and lipid accumulation.