bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of calcium oxalate monohydrate crystal aggregation by urine proteins
Authors: Hess B. , Nakagawa Y. , Coe F. L.
Published: December 2017

Normal urine inhibits both the growth and the aggregation of calcium oxalate monohydrate (COM) crystals but the molecules that inhibit aggregation are not well defined. We have developed a spectrophotometric assay method to measure the aggregation of COM crystals in vitro under conditions that avoid simultaneous crystal growth. At pH 7.2 and 90 mM NaCl, Tamm-Horsfall glycoprotein (THP) and nephrocalcin (NC), a major urinary inhibitor of COM crystal growth, inhibit COM crystal aggregation at concentrations as low as 2 X 10(-9) and 1 X 10(-8) M, respectively. When increasing NaCl to 270 mM or lowering pH to 5.7, inhibition by both glycoproteins, but more markedly by THP, is decreased. Urinary NC from calcium oxalate renal stone formers (SF NC) and NC isolated from calcium oxalate renal stones (stone NC) both inhibit COM crystal aggregation 10-fold less than NC from normal urine. Citrate is ineffective even at millimolar concentrations. Thus THP and NC are two major inhibitors of COM crystal aggregation in normal urine; SF NC and stone NC are defective aggregation inhibitors.
The role of thromboxane in two-kidney, one-clip Goldblatt hypertension in rats
Authors: Himmelstein S. I. , Klotman P. E.
Published: December 2017

Impaired contralateral kidney (CLK) function is important in the maintenance of hypertension in the two-kidney, one-clip (2K, 1C) Goldblatt rat model. Since glomerular filtration rate (GFR) is influenced by the products of arachidonic acid metabolism, we investigated the potential role of eicosanoids as mediators of impaired CLK pressure-volume regulation. At 4 wk following right renal artery clipping, GFR of hypertensive rats was significantly reduced. This decrease was due to the fixed reduction in GFR of the clipped kidney and failure of the CLK to increase its GFR. Thromboxane (Tx) production by isolated perfused CLK was significantly elevated, whereas prostacyclin production remained unchanged. Furthermore, CLK GFR was inversely proportional to Tx production. Treatment of 4-wk hypertensive animals with either the Tx synthase inhibitor UK-38,485 or the Tx receptor antagonist GR 32191 produced a significant increase in CLK GFR. In addition, treatment with either the Tx synthase inhibitor or the Tx receptor antagonist significantly reduced systemic blood pressure. Thus, in this 2K, 1C model of hypertension, increased renal Tx production prevents functional hypertrophy of the contralateral kidney. As a result, CLK pressure-volume regulation is impaired and systemic hypertension is maintained. Furthermore, Tx antagonists restore CLK function and acutely lower systemic blood pressure. Therefore, increased renal Tx production by the CLK appears to be an important mediator of hypertension in the 2K, 1C model.
Influence of renal sympathetic nerve stimulation on renal function in the primate
Authors: Echtenkamp S. F. , Dandridge P. F.
Published: December 2017

In anesthetized Macaca fascicularis monkeys renal sympathetic nerves were stimulated electrically while changes in renal function were measured. The range of stimulation frequencies was 0.25-4.0 Hz. In the primate the stimulation threshold for changes in renal vascular resistance at a renal perfusion pressure of 100 mmHg was between 1 and 2 Hz. Vascular resistance increased progressively at higher stimulation frequencies. The threshold for changes in sodium reabsorption was somewhat lower (between 0.5 and 1 Hz). At higher stimulation frequencies sodium excretion was dramatically reduced. Renin secretion was not significantly affected at 0.25 and 0.5 Hz stimulation and rose significantly only at stimulation frequencies of 1.0 Hz or above. Thus renal sympathetic nerves in the primate appear to influence renal vascular resistance and electrolyte excretion in a manner that is quantitatively similar to that seen in other species. However, in the primate it was not possible to stimulate renin secretion in the absence of changes in renal blood flow and sodium reabsorption.
Renal reabsorption of phosphate during development: transport kinetics in BBMV
Authors: Neiberger R. E. , Barac-Nieto M. , Spitzer A.
Published: December 2017

The mechanism responsible for enhanced reabsorption of phosphate (Pi) in growing animals was assessed in renal brush-border membrane vesicles (BBMV) prepared from 3- to 14-day-old and greater than 57-day-old guinea pigs. On standard diet, Vmax (pmol.mg-1.s-1) of Na+-Pi cotransport was higher (P less than 0.001) in newborn (650 +/- 77) than in adult (144 +/- 17) but Vmax of Na+-glucose cotransport did not differ with age. Low dietary Pi did not affect significantly Vmax of Na+-Pi cotransport in the newborn (P greater than 0.8) but increased it in the adult (to 318 +/- 32, P less than 0.05). A high Pi intake resulted in a smaller relative decrease in Vmax in the newborn than in the adult (27 vs. 44%, P less than 0.05). In the newborn, the serum Pi (mM) decreased on a low-Pi diet (from 1.8 +/- 0.1 to 0.8 +/- 0.1, P less than 0.001) and rose by twofold on the high-Pi diet (to 3.5 +/- 0.2, P less than 0.001). In the adult, there were no significant changes in serum Pi with changes in Pi intake (P greater than 0.5). Thus in the newborn the Na+-Pi cotransport system is characterized by high transport capacity but low adaptability to changes in dietary Pi.
Electrolyte, urea, and water transport in a two-nephron central core model of the renal medulla
Authors: Stephenson J. L. , Zhang Y. , Tewarson R.
Published: December 2017

A one-nephron model has been extended to include both short-looped and long-looped nephrons. Variables are volume flow, Na+, K+, Cl-, urea, hydrostatic pressure, and electric potential. The ratio of short-to-long-looped nephrons, one of the parameters of the model, is 5 to 1. With either rabbit or hamster permeability data from perfusion experiments, the model develops an osmolality of approximately 600 mosmol/l at the junction of inner and outer medulla but no osmolality gradient in the inner medulla. With the rabbit data, osmolalities in excess of 1,000 mosmol/l can be generated in the papilla with no active transport if urea permeabilities are less than 10(-5) cm/s; with the hamster data, electrolyte permeabilities must also be reduced. With these modified parameters, urea concentrations are less in the long loops than has been found on micropuncture. These can be increased to experimental levels by increasing the urea permeability and decreasing the hydraulic permeability of thin descending limbs in the inner half of the inner medulla, but to maintain loop osmolality at 1,000 mosmol/l it is necessary to postulate active NaCl transport in thin ascending limbs in the outer half of the inner medulla. This gives an alternative mode of concentration without active transport in the inner half of the inner medulla, in which electrolytes diffuse out of and urea diffuses into both limbs of Henle's loop and mix in the core with urea and water entering from the collecting duct. Concentration in either mode requires significant modification of perfusion data.
Development of H+ secretion by cultured renal inner medullary collecting duct cells
Authors: Brion L. P. , Schwartz J. H. , Lachman H. M. , Zavilowitz B. J. , Schwartz G. J.
Published: December 2017

The purpose of these studies was to characterize the development of H+ secretion by cultured inner medullary collecting duct (IMCD) cells. Differentiated IMCD cells derived from rat papillae develop in culture N-ethylmaleimide (NEM)- and dicyclohexylcarbodiimide (DCCD)-sensitive Na+-independent H+ pump, but showed substantial heterogeneity. Cells with pHi greater than or equal to 7.1, measured by 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF), showed more H+ pumping than did those with pHi less than 7.1. Quiescent cells in domes and in the center of growing nests often showed active H+ pumping activity, but rarely exhibited Na+-H+ exchange, whereas dividing cells at the periphery of the nests showed only Na+-H+ exchange. Differentiated IMCD cells also showed Na+-independent 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive Cl(-)-HCO3- exchange that functioned best when pHi was greater than or equal to 7.1, and homogenates of IMCD cells expressed carbonic anhydrase (CA) activity and CA II mRNA. A subgroup of IMCD cells avidly bound fluorescent peanut agglutinin (PNA); this binding became more extensive with time in culture. The PNA-labeled cells showed increased BCECF uptake, higher pHi, and more H+ pumping activity than did cells not binding PNA. They could be isolated by gel-immobilized PNA and in culture showed more CA activity and H+ pumping activity than unselected monolayers. The percentage of cells binding PNA correlated well with CA activity, indicating that this subgroup is better specialized to secrete H+. The appearance of PNA binding sites and the development of high CA activity may be characteristic of IMCD cell differentiation in culture.
Modulation of osteoblast function by prostaglandins
Authors: Yamaguchi D. T. , Green J. , Merritt B. S. , Kleeman C. R. , Muallem S.
Published: December 2017

The naturally occurring prostaglandins (PGs) were studied with respect to their abilities to change free cytosolic Ca2+ concentrations ([Ca2+]i), adenosine 3',5'-cyclic monophosphate (cAMP) levels, and cell proliferation in the osteoblastic cell line, UMR-106-01, and primary cultures of osteoblasts prepared from neonatal rat calvariae. All PGs tested stimulated an increase in [Ca2+]i, which was mainly due to Ca2+ release from intracellular stores. Measurements of the 50% effective concentration for the different PGs show that the potency ranking for PG-evoked [Ca2+]i increase in these cells is F2 alpha greater than D2 much greater than E2 greater than TxB2 greater than E1 greater than I2 much greater than A2. The PGs also increase cAMP levels in osteoblasts. At the highest concentrations tested (10-25 microM), dose-response saturation of cAMP production was observed only by PGE2 and PGE1. The potency rank for PG-stimulated cAMP increase was E2 greater than E1 much greater than A2 greater than I2 greater than F2 alpha greater than D2 greater than TxB2. Measurements of the effect of the PGs on thymidine uptake showed that low concentrations of PGF2 alpha and PGD2 had either no effect or stimulated proliferation of osteoblast-like cells. Relatively low concentration of PGE2, PGE1, and PGA2 inhibited proliferation. The potency ranking for PG-mediated inhibition of cell proliferation was identical to that found for PG-stimulated cAMP production. We conclude that all the naturally occurring PGs tested can activate the two signal transduction systems in osteoblasts.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of the ionic permeability of renal cortical brush-border membranes by cAMP
Authors: Lipkowitz M. S. , Abramson R. G.
Published: December 2017

The effects of adenosine 3',5'-cyclic monophosphate (cAMP) on potassium chloride permeability, relative ionic permeabilities, and Na+-dependent glucose transport were examined in rat renal cortical membrane vesicles. Brush-border membrane vesicles were prepared from paired control and cAMP- or forskolin-exposed homogenates by use of a magnesium aggregation technique. These studies demonstrate that exposure to exogenous cAMP or increases in endogenous cAMP significantly increase KCl permeability and ionic chloride permeability relative to that of potassium (PCl/PK) as determined with the fluorescent potential-sensitive probe 3,3'-dipropylthiadicarbocyanine iodide [diS-C3-(5)] and 36Cl uptake. Because PNa/PK did not change, PCl/PNa was also significantly increased by cAMP. These changes in ionic permeabilities were associated with a significant stimulation of Na+-dependent glucose transport that was unassociated with either an alteration in the kinetics of glucose transport or delayed dissipation of the inwardly directed Na+ gradient. These findings indicate that the cAMP-induced stimulation of glucose transport resulted from hyperpolarization of the vesicles secondary to the increase in PCl/PNa. These studies suggest that in vivo variations in intracellular cAMP concentration may modulate electrogenic transport processes by altering relative ionic permeabilities and membrane potential in renal proximal tubule cells.
Basolateral sodium-coupled acid-base transport mechanisms of the rabbit proximal tubule
Authors: Geibel J. , Giebisch G. , Boron W. F.
Published: December 2017

We studied Na+-coupled acid-base transport at the basolateral membrane of single, isolated, perfused rabbit proximal tubules by monitoring the time course of intracellular pH (pHi). The latter was determined using a microspectrofluorometric apparatus to alternatively excite the pH-sensitive fluorescent dye 2',7'-bis-2-carboxyethyl-5(and -6)-carboxyfluorescein (BCECF) at 440 and 490 nm, while the fluorescence emission, was measured at 530 nm. All experiments were conducted in the nominal absence of HCO-3 S1, S2, and S3 segments from both superficial and juxtamedullary nephrons were examined individually. We found that removing Na+ from both the lumen and bath (i.e., basolateral solution) caused pHi to fall from 7.24 to 6.75 in the superficial S1 segment (SS1), from 7.14 to 6.67 in the SS2, and from 7.09 to 6.69 in the SS3. Similarly, in juxtamedullary nephrons (J), bilateral Na+ removal caused pHi to fall from 7.25 to 6.76 in the JS1, from 7.16 to 6.71 in the JS2, and from 7.10 to 6.75 in the JS3. In all six proximal tubule subtypes, returning Na+ to the bath caused pHi to recover (i.e., increase). 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 50 microM), an inhibitor of HCO-3 transport systems, blocked this Na+-dependent pHi recovery in all three superficial subtypes and the JS3 but had no effect in either the JS1 or JS2. On the other hand, 50 microM ethylisopropyl amiloride (EIPA), an inhibitor of Na-H exchange, blocked the Na+-dependent pHi recovery in the JS1 and JS2 but had no effect in the JS3 or any of the superficial subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)
Bradykinin activates protein kinase C in cultured cortical collecting tubular cells
Authors: Dixon B. S. , Breckon R. , Fortune J. , Sutherland E. , Simon F. R. , Anderson R. J.
Published: December 2017

Bradykinin inhibits vasopressin-stimulated water transport in cortical collecting tubular cells. The biochemical mechanism of this effect was explored by means of primary cultures of rabbit cortical collecting tubular cells. Bradykinin was found to produce a rapid release of calcium from intracellular stores, an increase in sn-1,2-diacylglycerol levels, and a fivefold increase in membrane-bound protein kinase C activity, consistent with stimulation of phospholipase C and activation of protein kinase C in rabbit cortical collecting tubular cells. In addition, bradykinin produced a dose-dependent 46% inhibition of vasopressin-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) formation. Pretreatment with the protein kinase C inhibitors, H-7 and staurosporine, reversed the bradykinin-mediated inhibition of vasopressin-stimulated cAMP accumulation. In contrast, pretreatment with either the phospholipase A2 inhibitor, mepacrine, or pertussis toxin did not prevent the inhibitory effect of bradykinin on vasopressin-stimulated cAMP production, suggesting that the effects are not mediated by prostaglandin E2 or activation of a pertussis-toxin sensitive guanine nucleotide regulatory protein (e.g., Gi). Because bradykinin also inhibits isoproterenol-stimulated cAMP formation but does not inhibit either basal-, forskolin-, or cholera toxin-stimulated cAMP accumulation, the site of this inhibition appears to involve the hormone receptor or coupling of the receptor to the stimulatory guanine nucleotide regulatory subunit (Gs). The results demonstrate that bradykinin stimulates phospholipase C leading to activation of protein kinase C, which then inhibits vasopressin-stimulated cAMP production at the level of the hormone receptor or coupling of the receptor to Gs in cultured cortical collecting tubular cells.
Distribution of renin mRNA and its protein in the developing kidney
Authors: Gomez R. A. , Lynch K. R. , Sturgill B. C. , Elwood J. P. , Chevalier R. L. , Carey R. M. , Peach M. J.
Published: December 2017

The intrarenal distribution of renin changes markedly during maturation. To determine whether renin gene expression changes along the developing renal vasculature, renin mRNA distribution was assessed using in situ hybridization histochemistry. Fetal, newborn, and adult kidney tissue sections from Wistar-Kyoto rats were hybridized with an oligonucleotide complementary to rat renin mRNA. In fetal kidneys, renin mRNA was found in the vascular pole of juxtamedullary glomeruli and along afferent, interlobular, and arcuate arteries. In kidneys from newborn rats, renin mRNA localized throughout the whole length of afferent arterioles, but was not detected in interlobular or arcuate arteries. In adult kidneys, hybridization signals were less intense and confined to the juxtaglomerular apparatus. Immunolocalization of renin with a polyclonal anti-rat renin antibody paralleled closely the mRNA distribution. Northern blot analyses demonstrated that renin mRNA levels were higher in fetal and newborn (20- and 10-fold, respectively) than in adult kidneys. We conclude the following. 1) The fetal kidney expresses the renin gene. 2) Expression of the renin gene is subjected to developmental changes. 3) As maturation progresses, localization of renin synthesis and storage shifts from large intrarenal arteries to a restricted, classical juxtaglomerular site in the afferent arteriole.
Evidence that alteration of charge modifies proximal tubular shunt pathway permselectivity
Authors: Weinstein S. W. , Jones S. M. , Weinstein R. J.
Published: December 2017

Experiments were performed to test the hypothesis that membrane charge is an important determinant of paracellular pathway ion permselectivity in the proximal tubule. Net negative charge in or around the paracellular pathway should favor cation permeability; net positive charge should favor anion permeability. Therefore compounds such as amiloride and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), capable of changing net membrane charge, should predictably change the diffusive permselectivity of the paracellular pathway to anions and cations. In the first group of experiments amiloride, a compound capable of increasing net positive membrane charge, inhibited cation and enhanced anion diffusive permeability. In a second group of experiments, SITS, a compound capable of increasing net negative membrane charge, inhibited anion and enhanced cation diffusive permeability. The effects of amiloride and SITS were symmetrical; the lumen-to-bath and the bath-to-lumen diffusion potentials were not significantly different in magnitude. In addition these effects were completely and rapidly reversible. Our results suggest that amiloride increases net positive charge, and SITS increases net negative charge within the paracellular pathway. The most likely site for the actions of SITS and amiloride is the tight junction because the effects of the inhibitors were symmetrical. Both compounds act at low concentrations and reversibly such that removal of the inhibitor rapidly reverses its effects. We propose, on the basis of the ease with which these alterations in charge and thus paracellular pathway permselectivity occurred, that the permselectivity of this pathway may not be fixed and constant for any given proximal tubular segment. In fact, permselectivity may vary and thus serve as an important physiological control mechanism for proximal tubular solute and water reabsorption.
A D-mannose transport system in renal brush-border membranes
Authors: Mendelssohn D. C. , Silverman M.
Published: December 2017

Dog renal brush-border membrane vesicles (BBMV) from whole kidney cortex contain both low-affinity, high-capacity and high-affinity, low-capacity Na-dependent D-glucose cotransporters. D-Mannose is an epimer of D-glucose, differing in structure only in the axial, rather than equatorial, orientation of the hydroxyl group at the C-2 position of the pyranose ring. Uptake experiments of radioactive sugars into BBMV by standard Millipore filtration were performed to determine whether D-mannose shares either, or both, of the D-glucose carriers or if it is transported by an independent system. Transport of D-mannose occurs into an osmotically active space and is saturable and sodium dependent with a 1:1 Na:D-mannose stoichiometry, Km of 0.063 mM, Vmax of 3.6 nmol.mg-1.min-1, 25 degrees C, and pH 7.4. When an NaSCN electrochemical gradient was present, an “overshoot” was present, indicating active cotransport. Up to 50 mM D-mannose did not inhibit sodium-dependent D-glucose or alpha-methylglucoside uptake (0.01–20 mM). Sodium-dependent D-mannose uptake was inhibited by the following compounds in order of decreasing effectiveness: fructose greater than mannoheptulose greater than 2-deoxy-D-glucose greater than 2-fluoro-2-deoxy-D-glucose much greater than phloretin, cytochalasin B, galactose, 3-O-methyl-D-glucose, and L-mannose. Phlorizin also inhibited D-mannose uptake, but the high concentration required and the fact that a competitive pattern of inhibition could not be demonstrated contrasted with its effect on D-glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)
Functional studies in experimental renal cortical necrosis in the rat
Authors: Martinez-Maldonado M. , Lopez-Novoa J. M. , Fernandez-Repollet E. , Baldizon C. , Opava-Stitzer S. , Benabe J. E.
Published: December 2017

Necrosis of the outer two-thirds of the cortex (CN) was induced with boiling water in the left kidney of rats. Two days afterward, morphological damage was shown to be limited to the superficial cortex; deep nephron population was well-preserved. Glucose reabsorption under basal and glucose loading conditions, and extraction of p-aminohippurate, used as indices of proximal tubule integrity, were normal in control and experimental kidneys 48 h after cortical necrosis. Basal fractional water and electrolyte excretion did not differ between control and experimental kidneys. Calculated mean single-nephron glomerular filtration rate (GFR) and plasma flow for superficial (SupGFR and SupNPF) and juxtamedullary nephrons (JMGFR and JMPF) were similar to those obtained by micropuncture and Hanssen's technique for SupGFR, and for JMGFR by Hanssen's. Volume expansion led to a 27% increase in calculated SupGFR, but no change in JMGFR. The JMPF increased by 81%, whereas SupNPF increased by only 23%, suggesting that, in this model, GFR of deep nephrons may be independent of plasma flow. The results indicate that deep nephrons retain their functional integrity 48 h after cortical necrosis. After volume expansion fractional excretion of sodium was greater, and fractional water reabsorption less, in CN than in control kidneys. Thus handling of sodium and water by superficial and deep nephrons under basal conditions was similar, but reabsorptive capacity for deep nephrons of CN was lower during volume expansion. The present studies suggest that deep nephrons can maintain relatively normal function in cortical necrosis.
Modulation of ionic permeability in a nonpolarized cell: effect of cAMP
Authors: London R. D. , Lipkowitz M. S. , Sinert R. H. , Abramson R. G.
Published: December 2017

To evaluate whether adenosine 3',5'-cyclic monophosphate (cAMP) modulates ionic permeabilities of nonpolarized cells, as reported in diverse polarized epithelia, relative ionic permeabilities were determined in human red cell ghosts by means of the potential-sensitive fluorescent probe 3,3'-dipropylthiadicarbocyanine iodide. Relative ionic chloride permeability (PCl/PK), but not PNa/PK, was significantly increased in ghosts prepared from normal red blood cells (RBCs) exposed to cAMP analogues or forskolin, with the latter at a concentration that significantly increased intracellular cAMP concentration. As basal RBC cAMP concentrations of untreated uremic subjects were also increased, relative permeabilities of ghosts and unstimulated RBC cAMP concentrations were compared in normal, uremic, and dialyzed subjects, PCl/PK was significantly increased in uremic compared with normal subjects; PNa/PK was not altered. PCl/PK and RBC cAMP concentrations were indistinguishable in normal and dialyzed subjects. Neither the kinetics nor number of Cl(-)-HCO3- antiporters, assessed with the pH-sensitive probe acridine orange and the disulfonic stilbene 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, respectively, were altered in uremic cells. These studies suggest that cAMP modulates ionic chloride permeability via increased chloride conductance of each Cl(-)-HCO3- antiporter or by activation/opening of new or existing channels in RBC membranes.
Autoradiographic demonstration of oxytocin-binding sites in the macula densa
Authors: Stoeckel Marie Elisabeth , Freund-Mercier Marie Jose
Published: December 2017

Pages F310-F314: Marie Elisabeth Stoecke and Marie Jose Freund-Mercier. “Autoradiographic demonstration of oxytocin-binding sites in the macula densa.” We regret that the authors' corrections were not included in the final page proof.

(See PDF)
Xanthine oxidase: evidence against a causative role in renal reperfusion injury
Authors: Joannidis M. , Gstraunthaler G. , Pfaller W.
Published: December 2017

The conversion rates of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) were compared with the time course of in vivo lipid peroxidation (LPO) in an ischemia-reperfusion model of acute renal failure in the rat. LPO, measured as the renal release of malondialdehyde (MDA), was found to be markedly elevated only during the first 5 min of blood reflow following a 45-min interval of ischemia (arteriovenous MDA difference -277.3 +/- 53.5 vs. 3.7 +/- 5.7 nmol/l in controls, n = 14). After 30 min of reperfusion, arteriovenous MDA differences nearly reached control values (9.7 +/- 31.8 nmol/l, n = 7). In contrast to enhanced LPO, no significant conversion of XDH to XO was found (XO activity in controls: 23 +/- 1% of XO plus XDH activity vs. 26 +/- 3% after 45 min of ischemia, n = 7). Therefore XO-derived superoxide anion radicals cannot be considered causative for LPO in the reperfusion interval of experimental ischemic acute renal failure.
Effects of hypertonicity on ADH-stimulated water permeability in rat inner medullary collecting duct
Authors: Nadler S. P.
Published: December 2017

To assess the effects of increased tonicity on water reabsorption (Jv) in inner medullary collecting ducts (IMCD), antidiuretic hormone (ADH)-stimulated Jv and water permeability (PF) were determined in microperfused IMCD dissected from the inner medulla of rat kidney. In IMCD exposed to a 150-mosmol/kgH2O gradient in isotonic bath, ADH-stimulated PF averaged 719 +/- 93 microns/s. Symmetric addition of 75 mM NaCl to perfusate and bath resulted in a significant augmentation of ADH-stimulated PF (56%) that was reversible when initial solutions were restored. Despite the increase in PF, JV did not change but would have decreased by 16% (P less than 0.01) had PF not increased, because of the greater absolute axial increase in luminal tonicity that occurs with more hypertonic luminal solutions. When 150 mM mannitol was used to increase tonicity, similar effects were observed. However, 150 mM urea had no effect on ADH-stimulated PF. In IMCD exposed to 8-para-(chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, addition of 75 mM NaCl to both and perfusate also resulted in a 76% increase in PF. These results are the first to demonstrate directly that increased effective tonicity augments ADH-stimulated PF in rat IMCD at a site distal to adenosine 3',5'-cyclic monophosphate generation. This effect may contribute to maintenance of medullary interstitial tonicity during antidiuresis by ensuring that most water reabsorption occurs more proximally within the IMCD.
Influence of acute hyponatremia on renal ammoniagenesis in dogs with chronic metabolic acidosis
Authors: Halperin M. L. , Ching B. C.
Published: December 2017

The purpose of this study was to determine how acute hyponatremia might augment the excretion of ammonium in dogs with chronic metabolic acidosis. The excretion of ammonium was higher during hyponatremia because the proportion of ammonium produced that was excreted in the urine increased from 66% in controls to 77%. Effects on the production of ammonium are more complex. The rate of renal ammoniagenesis was not increased during hyponatremia in absolute terms nor when expressed per millimole of oxygen consumption. In contrast, this rate was somewhat higher during hyponatremia if expressed per millimole of sodium reabsorbed (9.8 vs. 10.3 mumol). The rate of oxygen consumption by the kidney did not fall, as anticipated, during hyponatremia; when this rate was expressed per millimole of sodium reabsorbed it rose from 46 to 55 mumol. There was no significant change in the rate of extraction of glutamine by the kidney, but there was a significant decrease in the rate of release of alanine during hyponatremia. Hence there appears to be more oxidation (yielding more ammonium) and less transamination of glutamine. We conclude that the renal events which led to a higher rate of excretion of ammonium during hyponatremia were a larger than expected rate of ammonium production owing to a greater rate of oxygen consumption together with lesser rate of transamination of the glutamine extracted by the kidney. In addition, more of the ammonium produced was transferred to the urine.
NaCl modulates captopril effects on glomerular prostaglandin synthesis and glomerular filtration
Authors: Rathaus M. , Podjarny E. , Pomeranz A. , Bernheim J.
Published: December 2017

Captopril stimulates glomerular prostaglandin (PG) synthesis and increases glomerular filtration rate (GFR) in Na-repleted rats, whereas, in Na-depleted rats, it fails to stimulate PG synthesis and decreases GFR. In the present work the influence of chronic and acute NaCl loading on PG synthesis and renal function was studied in Na-depleted rats receiving captopril (LNC rats). Glomerular PGE2 and 6-keto-PGF1 alpha were not increased in LNC rats and were significantly lower than in Na-depleted rats (LN). Na repletion, while continuing captopril, increased PG synthesis above control levels. Addition of captopril in vitro to the incubation medium stimulated PGE2 synthesis in glomeruli of control rats, whereas it depressed it in LN rats. Acute loading with NaCl in LNC rats increased inulin and PAH clearances to values significantly greater than in control rats and similar to those of normal rats receiving captopril. Comparable volume loading with isotonic mannitol or 3% albumin increased inulin and PAH clearances only to control values. The specific effect of NaCl in acute loading was prevented by cyclooxygenase inhibition and was not mediated by increased systemic blood pressure. The results provide evidence that the effects of captopril on glomerular PG synthesis and renal function depend on the state of Na balance.
Parathyroid hormone regulation of cytosolic Ca2+ in rat proximal tubules
Authors: Filburn C. R. , Harrison S.
Published: December 2017

The effect of parathyroid hormone (PTH) on cytosolic Ca2+ was studied on suspensions of purified rat renal proximal tubules using the fluorescent indicator quin-2. Rat PTH-(1-34) produced a transient 40% increase in apparent cytosolic Ca2+ at 20 s, followed by a rapid return toward the basal level. The half-maximal dose for both the rate of rise and peak apparent Ca2+ was 3 X 10(-8) M for rat PTH-(1-34). Unlike PTH, forskolin and dibutyryl adenosine 3',5'-cyclic monophosphate had no immediate effect. Bovine PTH-(3-34) blocked the effect of PTH in a concentration-dependent manner. Acute reduction of medium Ca2+ to less than 10(-6) M had no effect on either PTH- or angiotensin II (ANG II)-induced transients, but prevented any sustained increases. Washing tubules in nominally Ca2(+)-free medium followed by ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid reduced both transients by 50%. PTH at 2 X 10(-7) caused small (6-9%) increases in accumulation of [3H]inositol phosphates comparable with that produced by norepinephrine at 10(-7) M. At 10(-7) M, norepinephrine produced increases in Ca2+ and inositol phosphates similar to PTH; at 10(-5) M much larger increases in inositol phosphates occurred. Exposure to high levels of either norepinephrine or ANG II before PTH administration prevented any subsequent stimulation by PTH or other agonists. A submaximal dose of norepinephrine only slightly blunted the effect of PTH or ANG II.(ABSTRACT TRUNCATED AT 250 WORDS)
cAMP-stimulated rise of [Ca2+]i in rabbit connecting tubules: role of peritubular Ca
Authors: Bourdeau J. E. , Eby B. K.
Published: December 2017

Parathyroid hormone (PTH) increases cytosolic free Ca concentration ([ Ca2+]i) by mechanisms that depend on extracellular Ca in both cultured renal proximal tubules and isolated rabbit connecting tubules (CNTs). In CNTs 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) mimics this action, implicating cAMP as a second messenger, and part of the rise, due to increased luminal membrane Ca entry, is likely related to Ca absorption. In cultured proximal tubules the rise in [Ca2+]i, presumably mediated by increased Ca entry across the basolateral plasmalemma, activates gluconeogenesis and shortens microvilli. In the present study we examined cAMP-mediated Ca entry across the basolateral membranes of CNT cells, an effect potentially related to cell activation. Single CNTs were dissected from rabbit kidneys and loaded with fura-2. [Ca2+]i was measured by dual-wavelength excitation during perfusion of isolated segments in vitro. With 1.8 or 2.0 mM Ca in the lumen and the bath, suffusate 8-BrcAMP increased [Ca2+]i within minutes in a dose-dependent fashion. The increase persisted as long as 8-BrcAMP was present and reversed on its withdrawal. With 0.1 microM Ca in the lumen and the bath, 8-BrcAMP, but not ionomycin, failed to increase [Ca2+]i, implying that extracellular Ca is the major source. In tubules perfused with 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to eliminate luminal Ca, but suffused with 1.8 or 2.0 mM Ca, 8-BrcAMP increased [Ca2+]i (though less so than with Ca in the lumen), implying Ca entry across basolateral cell membranes. This rise in [Ca2+]i was attenuated markedly by the presence of 50 microM LaCl3 in the bath.(ABSTRACT TRUNCATED AT 250 WORDS)
Acute and subacute prostaglandin and ANG II inhibition on glomerulotubular dynamics in rats
Authors: Tucker B. J. , Blantz R. C.
Published: December 2017

Prostaglandins (PG) and angiotensin II (ANG II) contribute to regulation of glomerular microcirculation. Acute vs. chronic physiological alterations of glomerular hemodynamics that result from inhibition of either PG or ANG II, or both, and their interaction were examined. Four groups of Munich-Wistar rats were submitted to the following micropuncture studies in euvolemic conditions for measurements of glomerular hemodynamics and tubular fluid reabsorption: 1) an untreated control group, 2) 4- to 6-day inhibition of both PG and angiotensin-converting enzyme activity with meclofenamate and MK-421 (enalapril), 3) 4- to 6-day treatment with enalapril followed by acute PG inhibition in the second measurement period, 4) 4- to 6-day PG inhibition followed by acute enalapril treatment in the second period. Dual 4- to 6-day treatment decreased single-nephron filtration rate (SNGFR, 24 +/- 2 vs. 33 +/- 2 nl/min in control; P less than 0.05) as a result of decreases in single-nephron plasma flow (SNPF) and glomerular hydrostatic pressure gradient (delta P). Treatment with enalapril alone for 4-6 days did not reduce SNGFR and SNPF; however, delta P decreased. Acute addition of meclofenamate did not alter these factors. SNGFR was decreased with 4- to 6-day treatment of meclofenamate from 33 +/- 2 in control to 25 +/- 1 nl/min (P less than 0.05). Acute treatment with enalapril in the 4- to 6-day meclofenamate-treated rats increased SNGFR to values not different from control. The results demonstrated that glomerular hemodynamic alterations consequent to inhibition of ANG II and PG systems differ between chronic and acute treatments. Therefore, interpretation of the role of individual hormonal systems in the control of glomerular hemodynamics should be approached with caution, since effects may be altered by duration of treatment and involvement of other vasoactive systems.
Alanine protects rabbit proximal tubules against anoxic injury in vitro
Authors: Garza-Quintero R. , Ortega-Lopez J. , Stein J. H. , Venkatachalam M. A.
Published: December 2017

Rabbit proximal tubules were incubated aerobically or subjected to anoxia for 30 min followed by 60 min of reoxygenation. The medium contained (in mM) 5 glucose, 10 butyrate, 4 lactate or alpha-ketoglutarate (alpha-KG), and 1 alanine. Anoxic tubules in this medium were severely injured and recovered poorly. If the incubation medium was supplemented with additional alanine (up to 2.5 or 5 mM), then anoxic injury was prevented almost completely. Tubules in high-alanine medium showed modest elevations of ATP during anoxia. Comparable elevations of ATP were induced in anoxic tubules incubated with 4 mM alpha-KG and 5 mM aspartate without alanine. These substrates are metabolized anaerobically in the mitochondria to yield ATP. Surprisingly, anoxic tubules with alpha-KG and aspartate showed severe injury despite elevated ATP. If 5 mM alanine was also present, then additional increments of ATP did not occur, but injury was prevented. Examination of glucose metabolism failed to provide evidence for stimulation of anaerobic fermentations by alanine. These results suggest that alanine-induced cytoprotection during anoxia occurs by mechanisms not related to ATP synthesis, and that elevated ATP in alanine-supplemented tubules may be a result and not the cause of protection. Cytoprotection by alanine was shown to last for less than or equal to 90 min of anoxia. Glycine, a structurally related amino acid, also protects anoxic proximal tubules (J. Clin. Invest. 80: 1446, 1987). The mechanisms that underlie the cytoprotective effects of alanine and glycine remain to be determined.
Role of atrial natriuretic peptide in sodium balance in conscious spontaneously hypertensive rats
Authors: Seymour A. A. , Swerdel J. N. , Fennell S. A. , Kratunis V. J. , Asaad M. M.
Published: December 2017

Sodium and fluid intake were precisely regulated by 3 days of infusion of 0.07, 0.35, or 3.5 mu eq Na/min at rates of 25, 50, or 100 microliters/min in nine groups of conscious spontaneously hypertensive rats (SHR). At each level of sodium and volume intake, the acute depressor and renal responses to three doses of exogenous atrial natriuretic peptide (ANP)-(99-126) were determined in conscious, unrestrained SHR. The natriuretic responses to the highest dose of ANP-(99-126) (150 pmol/min) were independent of the rate of fluid infusion but were highly dependent on the sodium intake. The maximal increases in sodium excretion averaged 0.9 +/- 0.5 (253%), 2.6 +/- 0.5 (302%), and 15.4 +/- 2.1 mu eq.kg-1.min-1 (577%) in SHR maintained on 0.07, 0.35, and 3.5 mu eq Na/min, respectively. In addition, the diuretic but not the depressor responses to ANP-(99-126) were dependent on the sodium intake and were unrelated to the rate of fluid delivery. In separate groups of SHR, 3 days of infusions of 3.5 mu eq Na/min at 25 and 100 microliters/min significantly elevated plasma ANP from 89 +/- 16 to 200 +/- 60 and 159 +/- 24 fmol/ml, respectively. In conclusion, high sodium intake enhanced the renal responses to exogenous ANP-(99-126) despite increases in endogenous peptide concentrations in conscious SHR.
Ionic conductive properties of rabbit proximal straight tubule basolateral membrane
Authors: Welling P. A. , O'Neil R. G.
Published: December 2017

The ionic conductive properties of the nonperfused rabbit proximal straight tubule (S2) basolateral membrane were assessed by microelectrode techniques. The response of the basolateral membrane electrical potential difference, Vbl, to rapid changes in the peritubular bath concentration of K, HCO3, Na, and Cl were monitored with microelectrodes. The control steady-state Vbl averaged -41 mV (cell negative). An increase in peritubular bathing medium K concentration from 5 to 40 mM resulted in an instantaneous and sustained depolarization of +14.6 mV (27% of delta EK). Addition of barium (2 mM) depolarized the Vbl by +15.8 mV and abolished the Vbl response to the high-K medium. In other studies, reduction of peritubular bicarbonate at constant pH from 25 to 2.5 mM instantaneously and transiently depolarized Vbl by +15.8 mV (26% of delta EHCO3). In these same tubules reduction of peritubular Na from 126 to 2.2 mM resulted in an instantaneous and paradoxical depolarization of Vbl of +21.5 mV. Both depolarization transients resulting from reduction of Na and HCO3 were simultaneously inhibited by the addition of 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS; 0.5 mM), consistent with the presence of a SITS-sensitive Na-HCO3-coupled conductive pathway. In the absence of the bicarbonate buffer, reduction of Na resulted in a small sustained hyperpolarization of -5.8 mV (5% of delta ENa). Reduction of peritubular Cl from 120 to 4 mM resulted in an instantaneous and sustained depolarization of Vbl of +5.3 mV (6% of ECl) and was not affected by the addition of bumetanide (0.1 mM). It is concluded that the basolateral membrane of the nonperfused proximal straight tubule is characterized by a major barium-sensitive K conductance and a SITS-sensitive Na-coupled HCO3 conductance that carries net negative charge. These pathways are paralleled by relatively minor, but important, Na-conductive and Cl-conductive pathways.
Converting-enzyme inhibition abolishes polydipsia induced by dietary NaCl and K depletion
Authors: McKay A. J. , Poirier C. D. , Peterson L. N.
Published: December 2017

The present studies were designed to test the hypothesis that angiotensin II (ANG II) mediates nonosmotic thirst in animals fed the low-NaCl K-free diet by preventing the increased generation of ANG II using the converting-enzyme inhibitor, enalapril. Animals were fed either a control salt or low-NaCl K-free diet and were treated with or without enalapril. Water intake in rats fed the low-NaCl K-free diet increased more than twofold on day 3 and remained elevated over the 10-day period of study. Treatment with enalapril (40 mg.kg-1.day-1) 1) prevented the striking rise in plasma renin activity in rats fed the low-NaCl K-free diet, 2) led to complete blockade of the pressor response to a 50-ng injection of angiotensin I but not ANG II, 3) did not affect daily water intake in rats consuming the control salt diet, 4) did not reduce basal water intake in rats fed the low-NaCl K-free diet below values measured in control animals, and 5) did not abolish water intake in response to osmotic stimulation. However, enalapril treatment abolished the increase in water intake that occurs in animals fed the low-NaCl K-free diet. In a double crossover study using two groups of rats fed the low-NaCl K-free diet, enalapril prevented increased water intake in rats initially fed the low-NaCl K-free diet and rapidly inhibited increased water intake in rats fed the low-NaCl K-free diet after the high water intake had been established.(ABSTRACT TRUNCATED AT 250 WORDS)
Tubuloglomerular feedback and autoregulation in spontaneously hypertensive rats
Authors: Daniels F. H. , Arendshorst W. J. , Roberds R. G.
Published: December 2017

Experiments were conducted in 8-wk-old spontaneously hypertensive rats to determine whether tubuloglomerular feedback is essential for the autoregulation of renal blood flow. Autoregulation curves were obtained by measuring mean renal arterial blood pressure and flow during graded aortic occlusion. Renal vascular admittance was calculated from recordings of pulsatile renal arterial blood pressure and flow during induced atrial fibrillation. After a control period, acute ureteral obstruction was used to suppress tubuloglomerular feedback, as confirmed by measuring stop-flow pressure responses to rapid perfusion of Henle's loop. Ureteral obstruction did not impair steady-state autoregulation. During both the control and obstruction periods, the admittance gain was less than 1 at frequencies below 0.2 Hz, indicating dynamic autoregulatory activity. The control admittance contained two gain shoulders and two phase maxima, suggesting the presence of two control systems with response half-times of 1 and 10 s. During ureteral obstruction, the low-frequency shoulder and maximum disappeared, indicating that the slower system was no longer active. However, the high-frequency shoulder and maximum persisted, suggesting continued activity of the faster system. Collectively, these observations indicate the existence of a rapidly acting intrarenal control mechanism, in young spontaneously hypertensive rats, that may provide efficient autoregulation without assistance from tubuloglomerular feedback.
Basolateral cell membrane Ca-Na exchange in single rabbit connecting tubules
Authors: Bourdeau J. E. , Lau K.
Published: December 2017

Studies of cortical proximal nephrons and plasma membrane vesicles suggest that a Ca-Na exchanger regulates intracellular Ca2+ concentration ([Ca2+]i) in renal tubular cells. We tested this hypothesis in isolated perfused rabbit connecting segments by measuring [Ca2+]i with fura-2. Within 2 min of replacing bath NaCl with mannitol, [Ca2+]i rose from a base line of approximately 100 nM to a peak of approximately 650 nM, then declined to a plateau of approximately 500 nM for approximately 5 min before rising to a second peak of approximately 600 nM. [Ca2+]i returned toward base line after restoring bath NaCl. Substitution of choline Cl or tetraethylammonium chloride for bath NaCl reproduced the rise in [Ca2+]i, implicating the Na+ as the mediator. Selective bath (but not lumen) Ca removal or lumen Na deletion virtually abolished these effects, suggesting that bath Na deletion causes peritubular Ca influx by a process that depends on lumen Na. Lumen Na removal lowered, whereas its repletion increased, [Ca2+]i. Smaller increments in [Ca2+]i were produced by raising lumen [Na] from 0 to 35-55 mM or from 20 to 120 mM, but not from 55 to 150 mM. Clamping bath [Ca] at approximately 100 nM abolished the rise in [Ca2+]i produced by lumen Na, corroborating the role of peritubular Ca. These results suggest a Ca influx across the basolateral membrane that is driven by a cell-to-bath [Na] gradient and that can be activated by changes in lumen [Na]. We propose that this process, in part, regulates [Ca2+]i in the rabbit connecting tubule.