bluuebunny/crossref_metadata_2025 huggingface dataset:
Renal metabolic/excretory coupling
Authors: Spry L. A. , Rubinstein J. , Rettke C. , Zenser T. V. , Davis B. B.
Published: December 2017

Renal metabolic/excretory coupling is the enhancement of urinary excretion dependent upon renal metabolism. The nitrofurothiazoles, N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) and 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT), are model compounds used to study metabolic/excretory coupling. FANFT is deformylated to ANFT by renal deformylase enhancing ANFT excretion. In the rat, ANFT excretion after oral FANFT administration was 100-fold greater than ANFT excretion when ANFT was administered. FANFT and ANFT uptake into purified proximal tubules achieved equilibrium within 60 s and was demonstrated in nonviable tubules. FANFT partitioned into oil better than ANFT. Albumin inhibited FANFT and ANFT uptake into oil and decreased tubular uptake by 65%. Tubular FANFT uptake was threefold or greater than that of ANFT uptake with or without albumin. Renal deformylase was predominantly cytosolic and yielded apparent Km and Vmax of 6.7 microM and 6.1 nmol ANFT.min-1.mg protein-1, respectively. Deformylase activity was abolished by boiling, was specific for N-formylated compound, and was not altered by dinitrophenol treatment. Renal metabolic/excretory coupling for FANFT/ANFT combines energy-independent uptake with metabolism (deformylation), resulting in enhanced urinary ANFT excretion.
Calcifediol antagonizes PTH action on water and phosphate absorption in rabbit pars recta
Authors: Peraino R. A. , Rouse D. , Suki W. N.
Published: December 2017

Reports of the effects of calcifediol (25-hydroxycholecalciferol) on phosphate excretion, alone or with parathyroid hormone (PTH), or with adenosine 3',5'-cyclic monophosphate (cAMP), have been conflicting. The purpose of this investigation was to examine the effects on fluid and phosphate transport by the rabbit pars recta of calcifediol alone or with PTH. In tubule segments obtained from rabbits fed a normal diet, the addition of 10 or 30 nM calcifediol to the bath did not alter fluid absorption (Jv) or lumen-to-bath phosphate flux (JPil----b). However, pharmacological concentrations did inhibit Jv by 20.9 +/- 5.6% (100 nM, P less than 0.02) and 37.9 +/- 9.4% (1.0 microM, P less than 0.01) and JPil----b by 18.5 +/- 6.6% (100 nM, P less than 0.05) and 40.5 +/- 8.6% (1.0 microM, P less than 0.01). In the presence of 30 nM, 100 nM, or 1.0 microM calcifediol, neither 0.25 nor 1.0 U/ml PTH inhibited JPil----b. A modest decline in Jv did occur with 1.0 U/ml PTH in the presence of 30 nM and 100 nM calcifediol. Unlike calcifediol, when 10 nM calcitriol (1,25-dihydroxycholecalciferol) was present in the bath, 0.2 U/ml PTH significantly depressed Jv and JPil----b. To investigate the mechanism of action of high calcifediol concentration, measurement of the collected minus perfused tubule fluid chloride concentration difference was performed.(ABSTRACT TRUNCATED AT 250 WORDS)
Interactions of organic anions with the organic cation transporter in renal BBMV
Authors: Hsyu P. H. , Gisclon L. G. , Hui A. C. , Giacomini K. M.
Published: December 2017

It is generally assumed that the organic cation transport system in the renal proximal tubule is specific for organic cations and the transport of organic cations is not affected by organic anions. However, there are also data in the literature demonstrating that probenecid, a classical inhibitor of organic anion transport systems, inhibits the transport of an organic cation, cimetidine, in the renal proximal tubule. In this study we investigated the effects of probenecid and furosemide on the transport of N'-methylnicotinamide (NMN) the classical substrate of the organic cation transporter, in brush-border membrane vesicles prepared from rabbit renal cortex. In the presence of a pH gradient, both probenecid (10 mM) and furosemide reduced the initial uptake of NMN. Probenecid reduced the initial uptake of NMN to 12.1% of the control values (1.19 +/- 0.26 pmol/mg) and furosemide reduced the initial uptake of NMN to 39.2%. Probenecid (10 mM) also decreased the initial transport of NMN in the absence of a pH gradient. Inhibition of the transport of NMN by probenecid was concentration dependent, with the concentration of probenecid resulting in 50% inhibition of the transport of NMN equal to 2.31 +/- 1.18 mM in the presence of a pH gradient. Probenecid appeared to be a competitive inhibitor of NMN transport. The apparent Km (mean +/- SE) of NMN transport (2.01 +/- 0.78 mM) was increased to 18.7 +/- 10 mM (P less than 0.05) by probenecid (10 mM), whereas the Vmax was not changed (125 +/- 19.2 pmol.s-1.mg-1 vs. 186 +/- 94 pmol.s-1.mg-1, P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Phorbol myristate acetate and dioctanoylglycerol inhibit transport in rabbit proximal convoluted tubule
Authors: Baum M. , Hays S. R.
Published: December 2017

The present in vitro microperfusion study examined the effect of protein kinase C activation on transport in the rabbit proximal convoluted tubule (PCT). PCT were perfused with an ultrafiltrate-like solution and were bathed in a serumlike albumin solution. Addition of 5 x 10(-8) and 5 x 10(-7) M bath phorbol 12-myristate 13-acetate, an activator of protein kinase C, inhibited volume absorption from 1.06 +/- 0.10 to 0.77 +/- 0.07 nl.mm-1.min-1 (P less than 0.05) and 0.76 +/- 0.14 to 0.48 +/- 0.08 nl.mm-1.min-1 (P less than 0.01), respectively. Bath phorbol 12-myristate 13-acetate (5 x 10(-9) M) had no effect on volume absorption (Jv, 0.82 +/- 0.13 to 0.81 +/- 0.12 nl.mm-1.min-1). In contrast, 5 x 10(-8) M bath 4 alpha-phorbol, an inactive phorbol that does not activate protein kinase C, had no effect on Jv (0.95 +/- 0.14 to 0.94 +/- 0.11 nl.mm-1.min-1). Bath L-alpha-dioctanoylglycerol (10(-4) M), another known activator of protein kinase C, inhibited volume absorption from 0.96 +/- 0.08 to 0.71 +/- 0.08 nl.mm-1.min-1 (P less than 0.001). A 10-fold lower concentration of L-alpha-dioctanoylglycerol (10(-5) M) had no effect on Jv (0.81 +/- 0.18 to 0.78 +/- 0.17 nl.mm-1.min-1). Both 5 x 10(-8) M phorbol 12-myristate 13-acetate and 10(-4) M L-alpha-dioctanoylglycerol inhibited glucose, bicarbonate, and chloride transport in the PCT. These data are consistent with protein kinase C activation playing a role in the modulation of proximal tubular transport.
Vasoregulatory hormones and the hyperfiltration of diabetes
Authors: Bank N. , Lahorra M. A. , Aynedjian H. S. , Schlondorff D.
Published: December 2017

The role of renal vasoregulatory hormones in the hyperfiltration of early insulin-dependent diabetes mellitus (IDDM) was studied by micropuncture methods in rats with streptozotocin-induced diabetes. Seven to ten days after streptozotocin injection, untreated diabetic rats had elevated glomerular filtration rate (GFR) and single-nephron glomerular filtration rate (SNGFR), compared with normal euvolemic rats. Infusion of indomethacin (5 mg/kg) markedly reduced urinary and proximal tubular fluid prostaglandin E2 (PGE2), but GFR and SNGFR did not change. In a second group, intrarenal infusion of aprotinin (1,000 kallikrein inhibitor units.min-1.kg-1) to inhibit kallikrein also had no effect on GFR or SNGFR. In a third group, intrarenal infusion of angiotensin II (ANG II, 0.1 microgram.min-1.kg-1) reduced GFR, renal plasma flow (RPF), SNGFR, and glomerular plasma flow rate (QA) to values close to those in normal euvolemic rats. Single-nephron filtration fraction rose significantly with ANG II, but glomerular pressure (PG) was unaltered. Tubular fluid PGE2 increased in response to ANG II. Saralasin infusion following ANG II returned GFR, RPF, SNGFR, and QA to supernormal levels, and PG fell. In chronically salt-loaded normal rats, the responses to intrarenal ANG II and saralasin were similar to those observed in the diabetic rats. We conclude that hyperfiltration in early IDDM is not dependent on intact renal PGE2 or bradykinin synthesis. The results with ANG II infusion indicate that pre- and postglomerular and glomerular contractile cells of the diabetic kidney are able to constrict in response to this hormone.
Effect of Ca2+ on Cl- transport in thin ascending limb of Henle's loop
Authors: Kondo Y. , Yoshitomi K. , Imai M.
Published: December 2017

Effects of ambient Ca2+ concentration on Cl- transport across the thin ascending limb of Henle's loop (TAL) were examined by the in vitro microperfusion technique. When Ca2+ concentration in the bathing fluid was decreased from 1.5 mM to nominally 0 mM at 37 degrees C, the relative permeability of Cl- to Na+ (PCl/PNa) estimated from the NaCl diffusion voltage changed from 2.44 +/- 0.20 to 1.27 +/- 0.16 (n = 7, P less than 0.01). When Ca2+ concentration of the luminal fluid was reduced, PCl/PNa was unchanged. When Ca2+ concentration in the bathing fluid was changed from 4.5 to nominally 0 mM, the lumen-to-bath flux coefficient for 36Cl (K36Cl(l----b)) was decreased, whereas the value for 22Na was unchanged, indicating that the reduction of Ca2+ concentration in the bathing fluid selectively inhibits Cl- transport without affecting Na+ transport. By contrast, at 23 degrees C, the elimination of Ca2+ from the bathing fluid caused only a small reduction of PCl/PNa. Although at 23 degrees C acidification of the bathing fluid caused only little or no decrease in Cl- permeability, the elimination of Ca2+ from the bathing fluid under acid pH markedly suppressed the (K36Cl(l----b)) (10(-7) cm2/s). The pH titration curves of relative Cl- permeability examined at three different Ca2+ concentrations at 37 degrees C revealed that the interaction between proton and Ca2+ was noncompetitive. Addition of quin 2-AM, which reduced intracellular Ca2+ concentration, to the bath caused an irreversible suppression of Cl- permeability, suggesting that the decrease in intracellular Ca2+ concentration also inhibits the Cl- transport across the TAL.(ABSTRACT TRUNCATED AT 250 WORDS)
Remnant kidney hypermetabolism and progression of chronic renal failure
Authors: Harris D. C. , Chan L. , Schrier R. W.
Published: December 2017

To investigate the mechanisms whereby verapamil and dietary phosphate restriction slow progression of nephron loss after renal ablation, the effects of these maneuvers on inulin clearance (CIn), net sodium reabsorption (TNa+), oxygen consumption (QO2), and net glucose production (GP) were examined in isolated perfused normal and remnant kidneys. Preliminary studies characterized the isolated perfused remnant kidney perfusion. Adaptation to renal ablation was greater for QO2 (102% of normal), GP (138%), and kidney weight (79%) than CIn (51%) or TNa+ (40%). Verapamil (50 microM) lowered QO2 in remnant kidneys (1.64 +/- 0.24 vs. control 2.86 +/- 0.16 mumol.min-1.g-1, P less than 0.005), as did phosphate restriction (1.81 +/- 0.22 vs. control 3.05 +/- 0.40 mumol.min-1.g-1, P less than 0.05). These effects could not be accounted for by changes in CIn, TNa+, or GP and were not observed in normal kidneys. In summary 1) remnant kidneys are hypermetabolic compared with normal kidneys when assessed by QO2 and GP; 2) verapamil and phosphate restriction diminish the enhanced metabolic activity of remnant kidneys, an effect that is independent of TNa+; and thus 3) verapamil and phosphate restriction may slow progression of renal disease, at least in part by reducing renal metabolic demands.
Net proton influx into bone during metabolic, but not respiratory, acidosis
Authors: Bushinsky D. A.
Published: December 2017

During acute metabolic acidosis there is a net influx of protons into bone, decreasing the elevated proton concentration. Whether there is an influx of protons into bone during acute respiratory acidosis is not known. To determine the effect of respiratory acidosis on net proton flux (JH) relative to bone, we compared JH from neonatal mouse calvariae incubated for 3 h in medium acidified by an increase in PCO2 (respiratory acidosis) with that from calvariae incubated in medium acidified to the same extent by a decrease in bicarbonate concentration (metabolic acidosis). The initial medium pH with respiratory acidosis was not different from that with metabolic acidosis (7.108 +/- 0.005 vs. 7.091 +/- 0.007, respectively, P = NS). During respiratory acidosis there was no JH from bone relative to the medium (JH = 236 +/- 93 neq.bone-1.3h-1, P = NS vs. 0); however, during metabolic acidosis there was net proton influx from the medium into bone (JH = -703 +/- 108, P less than 0.05 vs. 0, P less than 0.001 vs. respiratory acidosis). There was less calcium efflux from bone during respiratory than during metabolic acidosis (JCa = 68 +/- 6 nmol.bone-1.3 h-1 vs. 100 +/- 9, respectively, P less than 0.001). There is a net influx of protons into bone in vitro during acute metabolic, but not during acute respiratory, acidosis. The smaller calcium efflux during respiratory acidosis may indicate less net bone mineral dissolution and thus less buffer release into the medium.
Modulation of cell nucleotide levels of isolated kidney tubules
Authors: Weinberg J. M. , Davis J. A. , Lawton A. , Abarzua M.
Published: December 2017

The mechanisms responsible for the large increases of intracellular ATP levels seen after isolated rabbit proximal tubules are treated with exogenous adenine nucleotides were studied. Exogenous ATP was rapidly degraded via adenosine as far as hypoxanthine. Degradation of AMP to adenosine was substantially inhibited by beta-glycerol phosphate. In studies of the ability of individual exogenous purines to increase intracellular ATP levels, single large doses of adenosine were less effective than equimolar doses of exogenous ATP but were substantially more effective than exogenous inosine or hypoxanthine. Exogenous guanine derived compounds increased only cell GTP. Incremental delivery of smaller doses of adenosine to maintain medium levels greater than 5 microM or inhibition of adenosine deaminase with erythro-9-[3-(2-hydroxynonyl)]adenine or 2'-deoxycoformicin enhanced the nucleoside's effectiveness. However, the initial increase of cell ATP was still greater after treatment with exogenous ATP than after adenosine and, in the presence of adenosine deaminase inhibition, larger increases of cell ATP were produced by 50 microM adenosine than by 250 microM adenosine. These observations are most consistent with substrate inhibition of adenosine kinase by adenosine. Furthermore, the adenosine kinase inhibitor, 5-iodotubercidin, prevented the increases of cell ATP resulting from exogenous adenosine or exogenous ATP. These studies demonstrate how the differential uptake and utilization characteristics of nucleosides and bases can fully account for the increases of intracellular nucleotides produced in isolated tubules by exogenous purines.
Prostanoids in renal failure induced by converting enzyme inhibition in sodium-depleted rats
Authors: Podjarny E. , Rathaus M. , Pomeranz A. , Shapira J. , Magen H. , Kariv N. , Bernheim J.
Published: December 2017

Clearances of inulin (CIn) and p-aminohippurate (CPAH) were measured in four groups of rats before and after intravenous administration of acetylsalicylic acid (ASA): 1) controls, on normal Na intake, 2) captopril-treated (30 mg.kg-1.day-1) on normal Na intake, 3) Na depleted, and 4) Na depleted, captopril-treated. In Na-depleted animals, CIn and CPAH were similar to controls but decreased significantly with ASA. In Na-depleted, captopril-treated rats, CPAH was slightly decreased, but CIn was significantly reduced (P less than 0.01). Both were not affected by ASA. Urine output was unchanged and the kidneys appeared normal on histological examination. The production of prostaglandins E2 (PGE2), F2 alpha (PGF2 alpha), and thromboxane B2 (TxB2) was measured in isolated glomeruli, cortical tubule suspensions, and medullary and papillary slices. Captopril increased PGE2 production by glomeruli and PGF2 alpha and TxB2 synthesis in papillary slices. Na depletion selectively enhanced the production of PGE2 by glomeruli and papillae. In contrast, the synthesis of prostanoids was significantly decreased in captopril-treated, Na-depleted rats. These findings suggest that in this model, functional nonoliguric renal failure may be related to abnormalities of prostanoid synthesis.
Angiotensin II and prostaglandins in control of vasa recta blood flow
Authors: Cupples W. A. , Sakai T. , Marsh D. J.
Published: December 2017

Angiotensin II has been implicated in the regulation of medullary blood flow and is known to interact with prostaglandins at sites within the kidney. Therefore the role of angiotensin in control of vasa recta blood flow was studied in antidiuretic, Munich-Wistar rats. We also tested the hypothesis that prostaglandins act to modulate the effect of angiotensin. Total renal blood flow was measured by an electromagnetic flow probe, vasa recta blood flow by a dual-slit method. Captopril was used to confirm that angiotensin blockade increased renal blood flow (by 15 +/- 4%). Captopril and saralasin were used to show that angiotensin blockade increased vasa recta blood flow (by 23 +/- 9 and 14 +/- 7%, respectively). The results demonstrate a tonic constrictor effect of angiotensin in the renal medulla. Exogenous angiotensin II, delivered intravenously, failed to mimic the effect of endogenous angiotensin. Indomethacin did not alter blood pressure or renal blood flow but did reduce vasa recta blood flow by 20 +/- 3%, suggesting that prostaglandins act preferentially on the medullary circulation. Nor did it alter the response of blood pressure, of renal blood flow, or of vasa recta blood flow to captopril. Moreover, prior angiotensin blockade with either captopril or saralasin enhanced the medullary vasoconstrictor effect of indomethacin (P less than 0.05). These results are not consistent with the hypothesis that prostaglandins act primarily as angiotensin modulators. They suggest that the medullary interaction between angiotensin and prostaglandins differs from that in the cortex.
Direct evaluation of the microvascular actions of ANP in juxtamedullary nephrons
Authors: Veldkamp P. J. , Carmines P. K. , Inscho E. W. , Navar L. G.
Published: December 2017

The renal vascular actions of atrial natriuretic peptide (ANP) remain incompletely understood. The purpose of this study is to evaluate the effects of ANP on microvascular structures of the normal kidney. The in vitro blood-perfused juxtamedullary nephron technique was utilized to allow visualization of arcuate arteries and afferent and efferent arterioles. Donor rats were pretreated with captopril to eliminate possible interactions between angiotensin II and atriopeptin III (AP III). The effects of topical administration of 3 nM AP III were determined by videometric analysis of vessel inside diameters. Under control conditions, arcuate arterial diameter averaged 83 +/- 14 microns (n = 7), afferent arteriolar diameter was 20 +/- 4 microns (n = 7), and efferent arteriolar diameter was 16 +/- 2 microns (n = 7). During superfusion with AP III, arcuate arteries and afferent arterioles dilated 73 +/- 9 and 23 +/- 5%, respectively. Both returned to their control values when AP III was removed from the superfusate. Further experiments on arcuate arteries (n = 5) revealed that 0.3 nM AP III also vasodilated these vessels (26 +/- 9%); however, no significant effect was elicited by 0.03 nM AP III. In contrast to the vasodilator influence of AP III on preglomerular vessels, efferent arteriolar diameter was not altered by AP III exposure. These observations reveal that AP III can induce selective preglomerular vasodilation involving arcuate arteries as well as afferent arterioles, while efferent arteriolar diameter is not perceptibly influenced.
Effect of direct increases in renal interstitial hydrostatic pressure on sodium excretion
Authors: Granger J. P. , Haas J. A. , Pawlowska D. , Knox F. G.
Published: December 2017

This study examined the effect of increases in renal interstitial hydrostatic pressure (PI) on sodium excretion (UNaV) utilizing a direct technique for increasing renal interstitial volume. PI was increased by renal interstitial volume expansion (RIVE) via injection of 50 microliters of a 2% albumin in saline solution into the renal interstitium through a chronically implanted interstitial catheter. RIVE resulted in a stable increase in PI (4.6 +/- 0.4 to 9.4 +/- 0.8 mmHg) that was sustained over a 30- to 40-min period without significant changes in renal blood flow or glomerular filtration rate. Increases in PI were associated with significant increases in urine flow (13.8 +/- 3.4 to 31.7 +/- 5.0 microliters/min) and UNaV (2.3 +/- 0.6 to 6.2 +/- 1.1 micro eq/min) and fractional excretion of Na (2.6 +/- 0.8 to 6.9 +/- 1.5%). To determine the importance of albumin in maintaining an elevated PI, the effects of renal interstitial injections of saline were compared with albumin in saline solution. Injection of 50 microliters of saline into the renal interstitium had no sustained effect on PI. Injection of 2% albumin in saline solution in the same group of rats resulted in significant elevations in PI and UNaV. These data indicate that direct increases in PI via renal interstitial volume expansion result in significant increases in UNaV, thus supporting a role for PI in controlling UNaV.
Transport of salicylate in proximal tubule (S2 segment) isolated from rabbit kidney
Authors: Schild L. , Roch-Ramel F.
Published: December 2017

The secretory and reabsorptive transport of salicylate was studied in the isolated and perfused rabbit proximal tubule (S2 segment). Salicylate secretion (Jb----lsal) fulfilled the criteria for a carrier-mediated transport system: Jb----lsal was saturable, was reversibly inhibited by probenecid, and occurred against a concentration gradient. The Km and Vmax for this secretory transport were 80 microM and 3,200 fmol.min-1.mm-1, respectively. At luminal pH of 7.4 and 6.6, salicylate reabsorption (Jl----bsal) was low (100 fmol.min-1.mm-1). Jl----bsal was stimulated by increasing the bath PCO2 or by removing basolateral HCO3-; Jl----bsal was inhibited by ethoxyzolamide and by SITS in the bath. Our results indicate that salicylate reabsorption depends on H+ secretion, consistent with reabsorption by simple nonionic diffusion. When salicylate was present in the lumen only, Jl----bsal increased after inhibition of the secretory transport by adding ouabain or probenecid in the bath or by lowering the bath temperature. These results are compatible with luminal recycling of salicylate, and suggest the presence of a mediated secretory transporter located at the luminal membrane.
Na+-independent D-glucose transport in rabbit renal basolateral membranes
Authors: Cheung P. T. , Hammerman M. R.
Published: December 2017

To define the mechanism by which glucose is transported across the basolateral membrane of the renal proximal tubular cell, we measured D-[14C]glucose uptake in basolateral membrane vesicles from rabbit kidney. Na+-dependent D-glucose transport, demonstrable in brush-border vesicles, could not be demonstrated in basolateral membrane vesicles. In the absence of Na+, the uptake of D-[14C]glucose in basolateral vesicles was more rapid than that of L-[3H]glucose over a concentration range of 1-50 mM. Subtraction of the latter from the former uptakes revealed a saturable process with apparent Km of 9.9 mM and Vmax of 0.80 nmol.mg protein-1.s-1. To characterize the transport component of D-glucose uptake in basolateral vesicles, we measured trans stimulation of 2 mM D-[14C]glucose entry in the absence of Na+. Trans stimulation could be effected by preloading basolateral vesicles with D-glucose, 2-deoxy-D-glucose, or 3-O-methyl-D-glucose, but not with L-glucose or alpha-methyl-D-glucoside. Trans-stimulated D-[14C]glucose uptake was inhibited by 0.1 mM phloretin or cytochalasin B but not phlorizin. In contrast, Na+-dependent D-[14C]glucose transport in brush-border vesicles was inhibited by phlorizin but not phloretin or cytochalasin B. Our findings are consistent with the presence of a Na+-independent D-glucose transporter in the proximal tubular basolateral membrane with characteristics similar to those of transporters present in nonepithelial cells.
Glucagon inhibits urinary acidification in the rat
Authors: Delahousse M. , Mercier O. , Bichara M. , Paillard M. , Leviel F. , Assan R.
Published: December 2017

The effects on urinary acidification of an acute infusion of glucagon (GLU) were studied by paired experiments in plasma-replete rats whose endogenous GLU secretion was restrained by a 0.7 ng.min-1.g body wt-1 somatostatin infusion. GLU did not affect the glomerular filtration rate in any of the plasma-replete rats studied. In 10 thyroparathyroidectomized (TPTX) rats and five intact rats subjected to hypotonic volume expansion, a low-dose (0.02 ng.min-1.g body wt-1) GLU infusion that raised the plasma GLU concentration from 302 +/- 63 to 1,010 +/- 140 pg/ml significantly increased the urinary bicarbonate excretion and decreased the urinary net acid excretion; a high-dose (0.05 ng.min-1.g body wt-1) glucagon infusion in the intact rats, that increased the plasma GLU concentration to 1,609 +/- 307 pg/ml, further enhanced the urinary bicarbonate excretion rate. In intact plasma-replete rats that were not subjected to a hypotonic volume expansion, low- and high-dose GLU infusions failed to affect the urinary bicarbonate excretion rate. Finally, no change in urinary excretion rates was noted in TPTX volume-expanded time control rats. We conclude that 1) physiological increments in plasma GLU concentration decrease urinary acidification by affecting the tubular H+/bicarbonate transport; 2) the bicarbonaturic effect of GLU may be blunted by the renal effects of high circulating antidiuretic hormone levels, or may be facilitated in an undetermined manner by hypotonic volume expansion.
Effects of angiotensin II and vasopressin on intracellular pH of glomerular mesangial cells
Authors: Ganz M. B. , Boyarsky G. , Boron W. F. , Sterzel R. B.
Published: December 2017

We investigated changes in intracellular pH (pHi) of cultured rat glomerular mesangial cells (MCs) exposed to angiotensin II (ANG II) and arginine vasopressin (AVP). pHi of quiescent MCs, passage 2–5, and grown on glass cover slips, was assessed by spectrofluorometry using the pH-sensitive dye, 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). The steady-state pHi of MCs in a pH 7.4, HCO3-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solution was 7.10 +/- 0.02 (n = 68) and in a pH 7.4, HCO3-containing solution, was 7.23 +/- 0.03 (n = 47) (P less than 0.01). The pHi recovery following an NH+4-induced acid load was inhibited by removal of Na+ from the bath or by addition of the amiloride analogue, ethyl isopropyl amiloride (EIPA). These effects were observed in MCs bathed in HEPES- or in HCO3-buffered solutions, consistent with the action of a Na+-H+ exchanger. When cells were bathed in HEPES, a 10-min exposure to ANG II or AVP (10(-10) to 10(-6) M) caused early and transient acidification of MCs (maximal pH change was -0.10), followed by gradual alkalinization (maximal pHi change +0.15 above the initial value). The increase of pHi was dependent on the presence of Na+ in the bath and was inhibited by EIPA. In the presence of HCO3, ANG II or AVP induced merely a small gradual acidification of MCs (pHi change -0.05). These findings demonstrate that MCs utilize a Na+-H+ exchanger for acid extrusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Proximal tubule Na+-K+-ATPase activity is inhibited during high-salt diet: evidence for DA-mediated effect
Authors: Bertorello A. , Hokfelt T. , Goldstein M. , Aperia A.
Published: December 2017

Locally produced dopamine (DA) causes a reversible and dose-dependent inhibition in Na+-K+-ATPase activity in rat proximal tubule (PT) segments [A. Aperia, A. Bertorello, and I. Seri. Am. J. Physiol. 252 (Renal Fluid Electrolyte Physiol. 21): F32–F45, 1987.]. To examine whether this effect might be of physiological importance, rats were given normal-salt (NS) or high-salt (HS) diet for 10 days. HS diet significantly increased Na excretion but did not alter glomerular filtration rate (GFR). Benserazide (Bz), an inhibitor of the enzyme L-aromatic amino acid decarboxylase (AADC) that converts L-dopa to DA, significantly attenuated the natriuresis in HS rats but had no effect on GFR. By use of immunofluorescence (IF) studies AADC was localized to the PT. Specific AADC IF was not observed in the medulla. In AADC-positive PT segments, Na+-K+-ATPase activity was significantly lower in HS rats than in NS rats (P less than 0.001). In AADC-negative medullary thick ascending limb, Na+-K+-ATPase activity was the same in NS and HS rats. If HS rats were given Bz just before study, PT Na+-K+-ATPase activity increased significantly and was not different from Na+-K+-ATPase activity in PT segments from NS rats. Bz had no significant effect on PT Na+-K+-ATPase activity in NS rats. In PT segments from Bz-treated rats, DA inhibited Na+-K+-ATPase activity already at a dose of 10(-8) M, whereas in segments from NS rats, significant inhibition of Na+-K+-ATPase activity was not observed until DA was increased to 10(-7) M.(ABSTRACT TRUNCATED AT 250 WORDS)
Flow dependence of bicarbonate transport in the early (S1) proximal convoluted tubule
Authors: Liu F. Y. , Cogan M. G.
Published: December 2017

We previously found, using an in vivo microperfusion pump rate of 30 nl/min, that proton secretion in the early (S1) proximal convoluted tubule (PCT) of the Munich-Wistar rat exhibited saturation kinetics. The maximal transport capacity was very high, approximately 500–600 peq.mm-1.min-1. The present studies assessed the change in early PCT acidification kinetics in response to an increase in microperfusion rate to 45 nl/min. First, bicarbonate permeability in the early PCT was measured and was found to be flow dependent. Proton secretion was then calculated using perfusate bicarbonate concentrations from 8 to 100 mM. Saturation of early proximal acidification (Vmax) still occurred at approximately 500–600 peq.mm-1.min-1, but the bicarbonate concentration effecting half-maximal acidification (apparent Km) decreased (from approximately 11 mM at 30 nl/min perfusion rate to less than 6 mM at 45 nl/min). By increasing luminal perfusion rate further to 60 nl/min at constant luminal bicarbonate concentration (25 mM), we confirmed that luminal flow rate did not affect the maximal level of acidification. Similar flow-dependent changes in acidification kinetics in the late PCT were also found, as has been previously shown. In conclusion, although an increase in luminal flow increased bicarbonate permeability and apparent affinity for substrate transport, there was no effect on maximal acidification rate in the early PCT.
AVP-induced Ca fluxes and contraction of rat glomerular mesangial cells
Authors: Takeda K. , Meyer-Lehnert H. , Kim J. K. , Schrier R. W.
Published: December 2017

Arginine vasopressin (AVP) is known to exert Ca mobilization and contraction in glomerular mesangial cells and vascular smooth muscle cells. However, the relationship between changes in intracellular Ca and transmembrane Ca fluxes is not clear at the present time. Therefore, this study was undertaken to determine the effect of AVP on cytosolic calcium ([Ca2+]i) and Ca fluxes as estimated by measurements of 45Ca2+ efflux. Changes of [Ca2+]i in response to AVP were directly measured in monolayers of adherent cultured mesangial cells. AVP induced rapid concentration-dependent increases in [Ca2+]i and Ca2+ efflux. AVP also induced contraction of mesangial cells. This effect was blocked only by the V1 (pressor)-antagonist, d(CH2)5Tyr(Me)AVP. Stimulation of Ca2+ efflux and changes in [Ca2+]i by AVP completely desensitized the mesangial cells to a subsequent identical challenge of AVP with no cross-tachyphylaxis to other hormones. Even in Ca2+-free medium, AVP increased [Ca2+]i and Ca2+ efflux, but to a lesser extent. Under this condition, contraction of mesangial cells induced by AVP was also observed. Readdition of extracellular Ca2+ following the AVP-induced increase in [Ca2+]i caused a second and slower [Ca2+]i increase. In Ca2+-containing conditions, lanthanum ion-reduced AVP evoked [Ca2+]i stimulation to the value observed in Ca2+-free medium. The Ca2+ channel blocker, verapamil, partially inhibited AVP-induced Ca2+ influx but totally blocked the increase in [Ca2+]i induced by high K. Verapamil did not inhibit AVP-stimulated Ca2+ efflux and cell contraction. Dantrolene, a blocker of Ca2+ release from endoplasmic reticulum, inhibited AVP-stimulated Ca2+ efflux and cell contraction.(ABSTRACT TRUNCATED AT 250 WORDS)
Cell membrane water permeabilities and streaming currents in Ambystoma proximal tubule
Authors: Tripathi S. , Boulpaep E. L.
Published: December 2017

An electrophysiological approach is used to analyze the possible routes of osmotically driven water flow across the isolated perfused Ambystoma proximal tubule. The minimum hydraulic conductivities (Lp) of the cell membranes were estimated from the initial rate of change of intracellular activities of Na+ and K+ in response to a step gradient of 50 or 100 mosmol/kg sucrose. The Lp of the apical membrane is 1.30 X 10(-4) cm.s-1.osM-1 referred to the luminal epithelial surface and 2.45 X 10(-6) cm.s-1.osM-1 when corrected for amplification of the brush border (n = 8). The Lp of the basolateral membrane is 1.42 X 10(-4) cm.s-1.osM-1 referred to the basement membrane surface and 6.39 X 10(-6) cm.s-1.osM-1 when corrected for the amplification of the basal and lateral membranes (n = 5). Transepithelial water flows were generated in either direction by a unilateral step increase of osmolality with 100 mosmol sucrose. Bath-to-lumen flow increased paracellular transepithelial resistance (R3) by 48%; lumen-to-bath flow decreased R3 by only 3%. A bilateral increase in the osmolality of both solutions by 50 mosM had no significant effect on R3. Streaming potentials were observed during trans-epithelial water flow induced by unilateral gradients of sucrose; their polarity, magnitude, site of generation, and insensitivity to change of paracellular resistance are all indicative of water flow through paracellular structures, especially the lateral intercellular spaces. Contrary to earlier suggestions (J. M. Diamond, J. Membr. Biol. 51: 195-216, 1979), these potentials are not primarily diffusion potentials across anion-selective tight junctions resulting from solute polarization in the unstirred layers. Instead, a true electrokinetic basis for these streaming potentials is indicated by their continued presence after deletion of all Cl-. Thus water moves through both cellular and paracellular pathways in this epithelium.
Effect of adenosine analogues on tubuloglomerular feedback responses
Authors: Schnermann J.
Published: December 2017

Adenosine has been invoked as a possible mediator of the vasoconstrictor response elicited through the tubuloglomerular feedback mechanism. These experiments were undertaken to study the effect of adenosine analogues on the magnitude of the stop-flow pressure (SFP) feedback response. With a control solution, maximum change of SFP during orthograde perfusion was 6.3 +/- 0.34 mmHg. When the adenosine1 (A1) receptor agonists CHA, CPA, or R-PIA were present in the perfusate in a concentration of 10(-5) M, SFP responses were significantly augmented and averaged 12.6 +/- 1.9 (P less than 0.001), 12.6 +/- 0.8 (P less than 0.001), and 10.3 +/- 1.1 mmHg (P less than 0.02), respectively. Diminished responses were seen at higher concentrations of A1 analogues. The A2-receptor agonist NECA did not significantly modify the control response at 10(-5) M, but reduced its magnitude at higher concentrations. During graded increases in loop flow rate essentially all of the response in the presence of CPA or R-PIA occurred in the 0-10 nl/min flow interval, whereas the most sensitive flow rate range in the control tubules was between 10 and 20 nl/min. In the presence of 10(-4) M furosemide SFP responses were abolished during perfusion with the control and NECA-containing solutions. In contrast, SFP fell by 11.8 +/- 1.26 mmHg and 8.7 +/- 1.25 mmHg with CHA or CPA solutions despite the presence of furosemide. Perfusion with 10(-6) M CPA in an isotonic mannitol solution was associated with a decrease of SFP by 16.3 +/- 1.42 mmHg, whereas the mannitol solution alone decreased SFP by only 0.6 +/- 0.18 mmHg. Our results show that luminal administration of A1-receptor analogues increases SFP feedback response magnitude, an effect that does not require the presence of a luminal NaCl signal.
Effect of PGE2 and alpha-adrenergic agonists on AVP-dependent cAMP levels in rabbit and rat CCT
Authors: Chabardes D. , Brick-Ghannam C. , Montegut M. , Siaume-Perez S.
Published: December 2017

The effect of prostaglandins and alpha-adrenergic agonists on arginine vasopressin-induced adenosine 3',5'-cyclic monophosphate (cAMP) production was investigated in microdissected rat and rabbit cortical collecting tubules (CCT) incubated in vitro. In rabbit CCT, addition to all media of a prostaglandin synthesis inhibitor increased this production; exogenous prostaglandin E2 (PGE2) induced a reproducible dose-dependent inhibition of cAMP accumulation. Maximal inhibition (mean: 57.5%) was observed with 0.3 microM PGE2, and threshold inhibition was observed with concentrations ranging from 3 to 10 nM PGE2. Inhibition of cAMP levels in rabbit CCT was also obtained with 0.3 microM PGF2 alpha (mean inhibition: 44.3%) but not with alpha-adrenergic agonists studied under the same conditions. The opposite was observed in rat CCT studied in parallel: the alpha-agonists inhibited cAMP production by up to 80%, but PGE2 had no effect.
Additive and synergistic interaction of atrial natriuretic peptide and volume expansion
Authors: Reddy S. , Kelly D. , Cochineas C. , Gyory A. Z.
Published: December 2017

To investigate whether atrial natriuretic peptides (ANP) are entirely responsible for the natriuresis of volume expansion (VE), we studied the natriuresis from acutely snared and nonsnared kidneys of rats undergoing sustained saline VE and subsequent infusion of maximal doses of ANP (atriopeptin II), or vice versa. Fractional excretion of Na (FENa) was increased from control (0.15 +/- 0.03%) to 4.6 +/- 0.6% by VE and to 10.9 +/- 1.5% by subsequent ANP infusion. With ANP alone FENa increased from control (0.24 +/- 0.04%) to 2.6 +/- 0.3%, and to 10.8 +/- 0.9% with VE, showing additive effects by both. Natriuresis with VE was significantly greater than with ANP alone (P less than 0.01) and both exhibited synergism, producing significantly greater natriuresis in the presence of the other than alone (P less than 0.05 for both). A reduction in perfusion pressure inhibited the effects of ANP and reduced that of VE. Natriuresis was produced by ANP independently of changes in glomerular filtration rate. It is concluded that 1) VE and ANP produce natriuresis by different renal mechanisms and that therefore, ANP can only account for part of the natriuresis of sustained VE; 2) the two have a synergistic interaction on natriuresis, probably through an intrarenal mechanism.
Prenatal glucocorticoids stimulate neonatal juxtamedullary proximal convoluted tubule acidification
Authors: Baum M. , Quigley R.
Published: December 2017

The rate of neonatal proximal convoluted tubule (PCT) HCO3 absorption is lower than that of adult animals. The present in vitro microperfusion study examined whether prenatal dexamethasone (60 micrograms/kg daily to the doe for 3 days before delivery) would accelerate the maturation of neonatal juxtamedullary PCT acidification. Control neonates studied within 48 h of birth had a urine pH of 7.06 +/- 0.15 and a urine HCO3 concentration of 34.3 +/- 7.0 meq/l. Animals receiving dexamethasone had a urine pH of 6.47 +/- 0.11 and a urine HCO3 concentration of 10.1 +/- 4.0 meq/l, both of which were significantly lower than control (P less than 0.01). In juxtamedullary PCTs perfused in vitro, volume absorption was 0.27 +/- 0.03 nl.mm-1.min-1 in controls and 0.39 +/- 0.02 nl.mm-1.min-1 in dexamethasone-treated animals (P less than 0.05). HCO3 absorption was stimulated in the dexamethasone group (52.6 +/- 4.6 vs. 34.1 +/- 6.3 pmol.mm-1.min-1, P less than 0.05); however, glucose transport was not significantly affected (24.8 +/- 1.3 in dexamethasone vs. 21.5 +/- 3.5 pmol.mm-1.min-1 in controls). Intracellular pH was measured using 2',7'-bis(carboxyethyl)-5(6)-carboxyflourescin to examine whether prenatal dexamethasone stimulated the apical Na(+)-H+ antiporter and the basolateral Na(HCO3)3 symporter. Apical Na(+)-H+ antiporter proton flux was 108.5 +/- 14.2 pmol.mm-1.min-1 in the control group and 250.7 +/- 31.3 pmol.mm-1.min-1 in the dexamethasone group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Maximal proton secretory rate of rat distal tubules is higher during chronic metabolic alkalosis
Authors: Wesson D. E. , Dolson G. M.
Published: December 2017

In vivo microperfusion studies show augmented proton secretion in the distal tubule of rats with chronic metabolic alkalosis. The present studies used the same technique to determine whether this augmented proton secretion is due predominantly to an increase in substrate affinity or alternatively to a predominant increase in the maximal proton secretory rate. Surface distal tubules of alkalotic and control rats were microperfused in vivo with solutions containing increasing concentrations of HCO3. Proton secretion was determined as the difference between measured net HCO3 reabsorption and passive HCO3 transport calculated by use of the permeability derived from perfusing with a HCO3-free solution. Proton secretion was expressed as a function of the initial luminal HCO3 concentration and was assumed to follow saturable Michaelis-Menten kinetics. Alkalotic animals had a significantly higher Km (33.9 vs. 21.6 mM, P less than 0.03) and Vmax (223.8 vs. 99.1 pmol.mm-1.min-1, P less than 0.001) compared with control. These data are consistent with the augmented proton secretion in the distal tubule of alkalotic animals as predominantly due to an increased maximal proton secretory rate rather than to increased substrate affinity.
Trans-stimulation effect on H(+)-organic cation antiport system in rat renal brush-border membranes
Authors: Katsura T. , Maegawa H. , Tomita Y. , Takano M. , Inui K. , Hori R.
Published: December 2017

Trans-stimulation effect on tetraethylammonium (an organic cation) transport was examined in rat renal brush-border membrane vesicles. The uptake of [14C]tetraethylammonium at pH 6.0-8.5 was stimulated by preloading the membrane vesicles with unlabeled tetraethylammonium. When the uptake was measured in preloaded membrane vesicles in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone, stimulation was observed at high pH but not at low pH. These results suggest that the mechanisms of the trans-stimulation effect on organic cation transport are different depending on the pH. When pH is low, the trans-stimulation is due to generation of an outward H+ gradient, which in turn stimulates [14C]tetraethylammonium uptake by H(+)-[14C]tetraethylammonium exchange. In contrast, when pH is high, the stimulation is due to direct exchange of tetraethylammonium for [14C]tetraethylammonium.
Effect of arginine depletion on glomerular and tubular kidney function: studies in isolated perfused rat kidneys
Authors: Radermacher J. , Klanke B. , Kastner S. , Haake G. , Schurek H. J. , Stolte H. F. , Frolich J. C.
Published: December 2017

The effect of L-Arg depletion on glomerular hemodynamics and tubular function of isolated rat kidneys perfused with a medium containing 21 amino acids has been studied. A cyclooxygenase inhibitor was added throughout for blockade of prostaglandin synthesis. Arg depletion caused significant (approximately 30%) reductions in renal perfusion flow rate (PFR, 13.9 +/- 1.2 vs. 19.8 +/- 0.6 ml.min-1.g (kidney wt-1), glomerular filtration rate (GFR, 598 +/- 79 vs. 924 +/- 42 microliters.min-1.g kidney wt-1), and urine flow rate (139 +/- 38 vs. 192 +/- 13 microliters.min-1.g kidney wt-1) compared with control kidneys, which were perfused with a physiological concentration of Arg (200 microM). Filtration fraction (FF) increased with Arg depletion (5.1 +/- 0.4 vs. 4.4 +/- 0.4%). Arg-depleted kidneys had a lower absolute sodium (TNa, 75.7 +/- 8.8 vs. 107.9 +/- 6.0 mumol.min-1.g kidney wt-1) and glucose reabsorption (T glucose, 3.7 +/- 0.6 vs. 5.6 +/- 0.5 mumol.min-1.g kidney wt-1), corresponding to a lower sodium and glucose filtration. Potassium handling and reabsorption of free water were not changed. Oxygen consumption (QO2) was lower in Arg-depleted kidneys (4.6 +/- 0.3 vs. 5.5 +/- 0.5 mumol.min-1.g kidney wt-1). The effects of Arg depletion were completely reversed by the addition of Arg (1 mM) at 120 min and partly reversed by the addition of citrulline (1 mM). Ornithine depletion or addition had no effect on PFR, GFR, FF, TNa, T glucose, and QO2. N omega-methyl-L-arginine, a specific inhibitor of nitric oxide endothelium-derived relaxing factor, produced the same effect as Arg depletion.(ABSTRACT TRUNCATED AT 250 WORDS)
Interleukin-1 beta and tumor necrosis factor-alpha synergistically stimulate nerve growth factor synthesis in rat mesangial cells
Authors: Steiner P. , Pfeilschifter J. , Boeckh C. , Radeke H. , Otten U.
Published: December 2017

Recent evidence indicates that cytokines are potent inducers of nerve growth factor (NGF) expression both in peripheral tissues and the central nervous system and that NGF, in addition to its neurotrophic action, also acts as an immunoregulatory agent. It was of interest to investigate whether inflammatory cytokines affect NGF production in renal mesangial cells, which play a crucial role in the modulation of the local immune function in the glomerulus. Our results show that the simultaneous addition of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) elicited a marked (13-fold) increase of NGF protein released by cultured rat glomerular mesangial cells within 24 h, whereas IL-1 alpha in combination with TNF-alpha, as well as the cytokines alone, did not promote the synthesis of NGF. The synergistic effect was dose dependent (maximal at 1 nM) and due to enhanced gene expression, since the cytokine treatment caused a fivefold increase in NGF mRNA after 8 h. Stimulation of NGF synthesis was abolished by mepacrine and dexamethasone, indicating that phospholipase A2 may be involved in NGF regulation. Moreover, pretreatment of the cells with the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) abolished induction of NGF by cytokines; in contrast, the specific cyclooxygenase inhibitors indomethacin and diclofenac failed to modify NGF production. These data suggest that a lipoxygenase metabolite produced in response to IL-1 beta and TNF-alpha acts as a mediator in NGF gene expression. In conclusion, these findings support a model in which a cytokine cascade including NGF may play an important role in the pathophysiology of inflammatory renal diseases.