bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of bumetanide on potassium transport and ionic composition of the arterial wall
Authors: Cantiello H. , Copello J. , Muller A. , Mikulic L. , Villamil M. F.
Published: December 2017

Bumetanide (B) (1 mM) decreased K content of dog carotid arteries (Ka) by 11-15%, K turnover (lambda 2) by 31%, and steady-state K fluxes (JK) by approximately 48%. The drug also reduced intracellular (ic) Cl, H2O, and occasionally ic Na. The half-maximal inhibitory concentration of B on JK was close to 40 microM. However, 10 microM still fully reduced ic K, Cl, and H2O but not ic Na. Replacement of external Cl by sulfate or nitrate mimicked the B effects on JK and reduced its capacity of inhibition by approximately 40 and approximately 80%, respectively. Replacement of Na by choline decreased Ka and JK by 90 and 96%, respectively, and rendered B totally ineffective. B also decreased Cl uptake and content of cultured vascular smooth muscle and ic Cl and H2O of whole arteries. Ouabain (Ou) (1 mM) decreased Ka 90%, accelerated lambda 2 four- to fivefold, and reduced JK 45%. Addition of B or removal of external Na or Cl in the presence of Ou returned lambda 2 to normal levels and reduced the residual JK by approximately 90% but failed to further decrease the Ka. According to these data, B mainly inhibits a coupled KCl passive self exchange plus a smaller active net KCl influx. Ou abolished the active component without affecting the passive self exchange. The presence of Na is necessary for the operation of the KCl-coupled self exchange, and Na gradients may provide the energy for the uphill KCl movements.
Acute renal denervation produces a diuresis and natriuresis in young SHR but not WKY rats
Authors: Rudd M. A. , Grippo R. S. , Arendshorst W. J.
Published: December 2017

Clearance experiments were conducted to determine the effect of acute unilateral renal denervation (DNX) on renal hemodynamics and salt and water excretion in anesthetized 6-wk-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto genetic control rats (WKY). Before DNX, SHR had higher mean arterial pressure (33%) and renal vascular resistance (RVR) (57%) and lower glomerular filtration rate (GFR) (10%); urine flow and sodium excretion were similar. Following DNX in SHR, sodium and water excretion increased by 138 and 62%, respectively (P less than 0.001); GFR and RVR were unchanged. In contrast, DNX in WKY did not affect urine flow (0%) or sodium excretion (-21%). These strain differences were observed in Okamoto-Aoki rats from two sources. Effective DNX was indicated by 95% reduction of norepinephrine content 3 days after DNX in both strains. Six-week-old Sprague-Dawley and Munich-Wistar rats, in contrast to WKY, responded to DNX with a natriuresis (+182%) and diuresis (+95%) (P less than 0.001). Renal function was unaffected by sham DNX in SHR. Our results indicate that efferent renal nerve activity has little tonic influence on the renal vasculature in these young rats. Augmented neurotransmitter release and/or tubular responsiveness may be involved in fluid and electrolyte retention and the pathogenesis of hypertension in SHR. Conversely, blunted renal neuroeffector responses may prevent WKY from developing hypertension.
Control of transepithelial Na+ transport and Na-K-ATPase by oxytocin and aldosterone
Authors: Girardet M. , Geering K. , Gaeggeler H. P. , Rossier B. C.
Published: December 2017

Short- and long-term effect of oxytocin on Na+ transport and Na-K-ATPase biosynthesis in the toad bladder, and the potential interaction of this hormone with aldosterone have been studied, leading to the following observations. An early Na+ transport response (oxytocin, 50 mU/ml) peaked at 10-15 min of hormone addition. At maximal stimulation a three- to fourfold increase in Na+ transport was observed, a sustained Na+ transport response (about two-fold control base line) was observed as long as the hormone was present in the medium and for up to 20 h of incubation. Pretreatment for 30 min with actinomycin D (2 micrograms/ml) did not inhibit the early response, but significantly impaired the sustained response, suggesting that de novo protein synthesis was required. The simultaneous addition of the two hormones led within 60 min to a marked potentiation of the action on Na+ transport. This synergism could be mimicked by exogenous cyclic adenosine monophosphate (cAMP). Oxytocin alone (18 h exposure, 50 mU/ml) increased the relative rate of synthesis of both alpha and beta subunits of Na-K-ATPase (1.9- and 1.6-fold, respectively; P less than 0.05), whereas aldosterone (80 nM) increased the relative rate of synthesis of the same subunits (2.6- and 2.2-fold, respectively; P less than 0.02). Finally, in contrast to what was observed at the physiological level, the interaction of oxytocin and aldosterone did not lead to a similar potentiation at the biochemical level, i.e., induction of Na-K-ATPase biosynthesis (2.7- and 2.9-fold, for alpha and beta subunits, respectively; P less than 0.025).
Effects of fasting on citrate transport by the brush-border membrane of rat kidney
Authors: Windus D. W. , Cohn D. E. , Heifets M.
Published: December 2017

Fasting in rats decreases plasma citrate levels and reduces urinary citrate excretion by the kidney. After 72 h of fasting, the endogenous renal citrate clearance was decreased and the fractional citrate excretion was 0.026 +/- 0.008 compared with 0.218 +/- 0.030 in control fed rats. To determine whether these findings result from an adaptation in citrate transport across the plasma membrane of the renal tubular cell, Na+ gradient-dependent [14C]citrate uptake was examined in brush-border membrane vesicles (BBMW) prepared from kidneys of fed and 72-h fasted rats. The initial rate (10 s) of Na+ gradient-stimulated uptake of 100 microM citrate was significantly increased in BBMW from kidneys of fasted rats (380 +/- 24.9 pmol/mg prot) compared with fed rats (255 +/- 24.9 pmol/mg prot). Arterial acid-base parameters from conscious animals were similar between the two groups. There was no significant difference in Na+-independent citrate uptake or in L-glutamine uptake measured at 20 s in BBMV from the kidneys of fasted compared with fed rats. An adaptation occurs in the brush-border membrane of the renal tubular cell of fasting rats, unrelated to systemic acidosis, that may result in increased reabsorption of citrate.
Lysine uptake by rat renal brush-border membrane vesicles
Authors: McNamara P. D. , Rea C. T. , Segal S.
Published: December 2017

Lysine uptake by isolated rat renal brush-border membrane vesicles occurs via a single saturable system plus a significant diffusion component with indication of a single energy of activation on an Arrhenius plot. Initial uptake is not sodium dependent, and intravesicular accumulation of lysine at longer time points is greatest in the absence of sodium. Accumulation levels differ in the presence or absence of NaCl or choline chloride and are specific for the cation used. Lysine uptake is membrane potential sensitive and inhibitable by cystine, dibasic amino acids, and cycloleucine. Heteroexchange diffusion of lysine with cystine and lysine with arginine occurs, but no heteroexchange occurs with cycloleucine, indicating that lysine shares a transport system with cystine and dibasic amino acids but not with cycloleucine.
A mechanism by which atrial natriuretic factor mediates its glomerular actions
Authors: Appel R. G. , Wang J. , Simonson M. S. , Dunn M. J.
Published: December 2017

Differential in vivo glomerular effects of atriopeptin I (AP I) and atriopeptin III (AP III) were studied in parallel with in vitro physiological and biochemical parameters. In anesthetized Sprague-Dawley rats, AP III, but not AP I, significantly increased glomerular filtration rate. Image analysis microscopy was used to assess the effect of AP I and AP III on angiotensin II (ANG II)-induced contraction of cultured rat glomerular mesangial cells. AP III, but not AP I, inhibited ANG II-induced mesangial cell contraction in a concentration-dependent manner. Additional inhibitory agents included exogenous DBcGMP, 8-BrcGMP, Na nitroprusside, and DBcAMP. AP III stimulated mesangial cell cGMP with a lower threshold and greater maximum stimulation than AP I. Neither agent stimulated cAMP accumulation. Since mesangial cell contractility may regulate the glomerular capillary surface area, these results suggest that AP III partially mediates its glomerular effects through inhibition of ANG II-induced mesangial cell contraction. Whereas cGMP is not clearly implicated as the mediator of this effect, it appears that both cGMP and cAMP may regulate the state of mesangial cell contractility.
Carrier-mediated reabsorption of small peptides in renal proximal tubule
Authors: Ganapathy V. , Leibach F. H.
Published: December 2017

Recent studies with a variety of tissue preparations in the kidney have demonstrated that proximal tubular cells possess specific transport systems for di- and tripeptides. In contrast to the well-known amino acid and glucose transport systems, active transport of peptides in these cells is energized by an H+ gradient rather than an Na+ gradient. Like amino acid-Na+ and glucose-Na+ cotransport systems, peptide-H+ cotransport is electrogenic and hence a membrane potential also contributes to the uphill transport of peptides in these cells. Di- and tripeptides that are filtered at the glomerulus, as well as those that are produced in the tubular lumen from larger polypeptides by the action of brush-border peptidases, serve as substrates for the renal peptide transport system under physiological conditions. The H+ gradient that is necessary to drive renal peptide transport is generated in vivo by concerted action of the basolateral Na+-K+-ATPase and the brush-border Na+-H+ exchanger. The peptidases and the peptide transport system in the renal brush-border membrane play a significant role in the reabsorption of peptide-bound amino acids as well as in the regulation of plasma levels of small peptides.
Glomerular angiotensin II receptor modulation in glycerol-induced acute renal failure
Authors: Wilkes B. M. , Mento P. F.
Published: December 2017

The objective of this study was to examine the relationship between plasma angiotensin II (ANG II) and ANG II receptor binding to the glomerulus following acute renal failure (ARF) induced by an injection of glycerol (50%, 10 ml/kg im). At 2 and 24 h after glycerol injection, ARF was documented by a rise in blood urea nitrogen (BUN) (normal, 18.6 +/- 0.7; 2 h after glycerol 29.3 +/- 2.3; 24 h after glycerol, 103.0 +/- 12.0 mg/dl; P less than 0.002 each experimental vs. normal) and creatinine (normal, 0.41 +/- 0.02; 2 h after glycerol, 0.96 +/- 0.10; 24 h after glycerol, 2.40 +/- 0.30 mg/dl; P less than 0.001, experimental vs. normal groups). Plasma ANG II rose from a control of 15.8 +/- 3.1 to 26.9 +/- 4.4 pg/ml at 2 h and 49.5 +/- 8.6 pg/ml at 24 h after glycerol (P less than 0.05, experimental vs. normal). No changes in affinity or density of glomerular ANG II receptors were detected either at 2 or 24 h after glycerol injection despite the significant rise in plasma ANG II (glomerular ANG II receptors: normal, 1,000 +/- 61; 2 h after glycerol, 896 +/- 120; 24 h after glycerol, 936 +/- 80 fmol/mg). The 24-h infusion of ANG II in normal rats to achieve plasma levels identical to the 24 h ARF group caused ANG II receptor density to fall to 58.1 +/- 8.6% of control values (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Dopamine causes inhibition of Na+-K+-ATPase activity in rat proximal convoluted tubule segments
Authors: Aperia A. , Bertorello A. , Seri I.
Published: December 2017

We studied the effect of dopamine (DA) on Na+-K+-ATPase activity in proximal convoluted tubule (PCT) segments dissected from perfused rat kidneys. DA inhibited Na+-K+-ATPase activity in a dose-dependent manner. Inhibition was significant with 10(-7) M DA and maximal with 10(-4) M DA. The inhibition was reversible. Enzyme inhibition occurred in the presence of DA and a DA antagonist, metoclopramide, but not when 10(5) M of the DA1 and DA2 agonists fenoldopam mesylate and LY 171555 were added in the absence of DA. In PCT segments incubated with the DA precursor dopa, Na+-K+-ATPase activity was also inhibited. However, dopa did not inhibit the sodium pump if dopa decarboxylase activity was blocked with benserazide. These findings suggest an intracellular site of action of DA. In tubules incubated in different K concentrations, 10(-5) DA decreased the maximal activity (Vmax) and increased the Km. DA 10(-5) M caused an almost immediate swelling of PCT segments. Swelling did not occur in the presence of both DA and 10(-5) M amiloride. The DA-induced tubular swelling was probably due to inhibition of Na+-K+-ATPase-mediated Na+-transport. We conclude that in rat PCT segments, DA causes a rapid and reversible inhibition of apparent Na+-K+-ATPase activity and an apparent reduction in the affinity for K. The site of action appears to be intracellular.
PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and TxB2 synthesis along the rabbit nephron
Authors: Farman N. , Pradelles P. , Bonvalet J. P.
Published: December 2017

The capacity of synthesis of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), 6-keto-PGF1 alpha, and thromboxane (TxB2) along the rabbit nephron was determined. A sensitive enzyme immunoassay was applied to isolated nephron segments, from the glomerulus to the terminal collecting tubule. The three prostaglandins and thromboxane (PG) were measured on the same samples after incubation in the presence of arachidonic acid. In the glomerulus, PGE2 synthesis (29.4 +/- 3.3 pg X glomerulus-1 X 30 min-1) represented 60% of the sum of the four PGs. PGF2 alpha and 6-keto-PGF1 alpha represented 22 and 17%, respectively, and TxB2 1.4%. The contribution of each PG to tubular synthesis was different, since at least 90% of PG synthesis consisted of PGE2. In the medullary collecting tubule (MCT), by far the major tubular site of PG synthesis, it was 809.6 +/- 140.8 pg X mm-1 X 30 min-1 for PGE2, 17.7 +/- 7.2 for PGF2 alpha, 8.3 +/- 1.9 for 6-keto-PGF1 alpha and 0.24 +/- 0.08 for TxB2. These relative proportions were roughly respected all along the tubule. Values were much lower in the convoluted and straight portions of the proximal tubule (proximal convoluted tubule: PGE2 8.2 +/- 2.0, PGF2 alpha 0.4 +/- 0.06, 6-keto-PGF1 alpha 0.26 +/- 0.04, TxB2 0.017) and the medullary and cortical thick ascending limb of the loop. They increased regularly along the distal structures of the tubule (light portion of the cortical collecting tubule (CCT1): PGE2 228.3 +/- 20.4, PGF2 alpha 4.34 +/- 0.6, 6-keto-PGF1 alpha 1.8 +/- 0.3, TxB2 0.22 +/- 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of insulin on renal potassium metabolism
Authors: Rossetti L. , Klein-Robbenhaar G. , Giebisch G. , Smith D. , DeFronzo R.
Published: December 2017

The effect of insulin on renal potassium excretion was examined by employing the euglycemic insulin clamp technique in combination with renal clearance measurements. While euglycemia was maintained, insulin was infused at rates of 4.8 (n = 7) and 12 (n = 5) mU X kg-1 X min-1. Steady-state plasma insulin levels of 164 +/- 8 and 370 +/- 15 microU/ml were achieved in the low- and high-dose studies, respectively. Base-line plasma potassium concentration declined progressively by a mean of 0.14 +/- 0.09 (P less than 0.05) and 0.40 +/- 0.05 meq/liter (P less than 0.01) during the low- and high-dose insulin infusion protocols. Urinary potassium excretion did not change significantly from base line with either insulin dose. Because the decline in plasma potassium concentration could have masked a stimulatory effect of insulin on UKV, six rats received a 12-mU X kg-1 X min-1 euglycemic insulin clamp in combination with an exogenous potassium infusion to maintain the plasma potassium concentration constant at the basal level (4.03 +/- 0.03 vs. 4.05 +/- 0.05 meq/l). Under these conditions of normokalemia, insulin augmented UKV 2.4-fold, from 0.20 +/- 0.05 to 0.48 +/- 0.04 meq/l (P less than 0.001).
Thick ascending limb response to dDAVP and atrial natriuretic factor in vivo
Authors: Peterson L. N. , De Rouffignac C. , Sonnenberg H. , Levine D. Z.
Published: December 2017

Because of the inaccessibility of the thick ascending limb (TAL) to micropuncture, it has been difficult to evaluate the effects of ADH and atrial natriuretic factor (ANF) on TAL salt transport in vivo. The purpose of the present study is to assess the effects of these hormones on TAL NaCl reabsorption in vivo. Although passive NaCl permeability and unidirectional Na fluxes were not measured, the microstop-flow conductivity technique that was used in these studies controls solute delivery, permits the measurement of the rate of net NaCl reabsorption, and tests the capacity of the TAL to establish a limiting gradient. Despite the presence of a dramatic natriuretic response, a natural extract of ANF did not significantly increase the minimum NaCl concentration reached by the TAL after 60 s of stop-flow. However, 1-[desamino]-8-D-arginine vasopressin (dDAVP) increased by 23%, the rate at which luminal Na concentration declined, and reduced by 28% the minimum NaCl concentration achieved by the TAL. Therefore, these results do not demonstrate a significant direct peritubular effect of ANF on TAL NaCl permeability in outer cortical nephrons, but support a role for antidiuretic hormone in enhancing TAL NaCl reabsorption in vivo.
Lithium clearance in mineralocorticoid escape in humans
Authors: Boer W. H. , Koomans H. A. , Dorhout Mees E. J.
Published: December 2017

Lithium clearance (CLi) has been advanced as an indicator of Na delivery from the proximal tubules. We studied CLi in eight healthy males before and after mineralocorticoid escape, a maneuver that may induce suppression of fractional proximal Na reabsorption (FPRNa). FPRNa was also estimated from changes in maximal free water clearance (CH2O). According to the latter method, FPRNa dropped from 85.7 +/- 2.2 to 81.3 +/- 3.4%, whereas inulin clearance rose from 125 +/- 11 to 149 +/- 15 ml/min. The changes in CLi were surprisingly large, from 40.6 +/- 7.6 to 75.8 +/- 18.4 ml/min. If lithium is a valid marker of Na handling in the proximal tubule in humans, this change would imply a fall in FPRNa from 67.5 +/- 3.9 to 49.7 +/- 9.0%, suggesting a much larger shift in tubular Na reabsorption in escape than hitherto suspected. In addition, it would suggest that the inevitable back diffusion of a part of the solute-free water in the distal nephron, and thus overestimation of FPRNa by the CH2O method, increases importantly during escape. Alternately, lithium may not be a good marker of proximal tubular Na handling. For instance, both lithium reabsorption and escape may take place beyond the proximal tubule, or lithium may be excreted in the distal nephron in certain conditions. Present methods do not permit further analysis of these options in the human model.
Effect of stimulated neutrophils on cyclic nucleotide content in isolated rat glomeruli
Authors: Basci A. , Wallin J. D. , Shah S. V.
Published: December 2017

In this study we examined the effect of cell-free supernatants from stimulated neutrophils on the adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) content in isolated rat glomeruli. Cell-free supernatants obtained from unstimulated and stimulated (with opsonized zymosan for 30 min at 37 degrees C) cells were incubated for 5 min with glomeruli and tubules. Cell-free supernatants from stimulated neutrophils significantly increased the cAMP content in the glomeruli from 34.7 +/- 2.3 to 99.7 +/- 7.0 pmol/mg protein (n = 23; P less than 0.001). The cAMP content in the tubules and the cGMP content in the glomeruli or tubules was not altered by the cell-free supernatants from stimulated neutrophils. The cAMP response of the glomeruli was not modified when supernatants were obtained from neutrophils stimulated in the presence of superoxide dismutase, a scavenger of superoxide anion. In contrast, the glomerular response to supernatants obtained from neutrophils stimulated in the presence of catalase, a scavenger of hydrogen peroxide, or in the presence of methionine or taurine, scavengers of hypochlorous acid, was significantly reduced (P less than 0.001). Additional experiments that used prostaglandin synthesis inhibitors (meclofenamate and ibuprofen) and phospholipase inhibitor (quinacrine) suggested that the reactive oxygen metabolites increase the cAMP content in glomeruli by stimulating phospholipase activity and thus enhancing prostaglandin synthesis. These data show that reactive oxygen metabolites generated by stimulated neutrophils increase cAMP content in glomeruli and suggest that neutrophils may modulate the glomerular function and the inflammatory response in glomerular disease by altering the cAMP content.
The kidney in potassium depletion. I. Na+-K+-ATPase activity and [3H]ouabain binding in MCT
Authors: Hayashi M. , Katz A. I.
Published: December 2017

The effect of potassium depletion on renal Na+-K+-ATPase was studied in rats. K depletion produced a striking, time-dependent increase in Na+-K+-ATPase activity of the outer medullary collecting tubules (inner stripe; MCTis). After 3 wk on the K-free diet, when the urine was almost potassium-free, Na+-K+-ATPase activity in MCTis was over fourfold higher than in control animals (2,964 +/- 185 vs. 645 +/- 108 pmol X mm-1 X h-1). Repletion of potassium restored enzyme activity to base line within 7 days (t1/2 = 3.8 days), which corresponds to the catabolic rate of the renal enzyme, suggesting the cessation of enhanced synthesis that took place during K deprivation. Changes in Na+-K+-ATPase activity and aldosterone levels during both K depletion and repletion occurred in opposite directions and were therefore independent of each other. [3H]Ouabain binding to intact MCTis, reflecting the number of pump sites on the basolateral membrane, was similar in K-depleted and control animals; in contrast, tubule permeabilization that exposes additional pump units to the ligand, unmasked a nearly fourfold increase in [3H]ouabain binding (50.0 +/- 6.8 vs. 13.2 +/- 1.7 fmols X mm-1) in K-depleted rats, comparable to the increment in Na+-K+-ATPase activity. These results show that K depletion leads to a marked increase in Na+-K+-ATPase activity of MCTis, and suggest that the new enzyme units are located at a ouabain-inaccessible site in the intact tubule, i.e., either in an intracellular compartment or at the luminal membrane, where they may be involved in potassium reabsorption.
Ca-activated K channels in apical membrane of mammalian CCT, and their role in K secretion
Authors: Frindt G. , Palmer L. G.
Published: December 2017

High conductance, Ca-activated K channels were studied in the apical membrane of the rat cortical collecting tubule (CCT) using the patch-clamp technique. In cell-attached patches the channels were found mainly in the closed state at the spontaneous apical membrane potential. They spent progressively more time in the open state as the pipette potential was made negative relative to the bath. In excised patches these channels had a high selectivity for K over Na and were activated by micromolar concentrations of Ca2+ on the cytoplasmic side of the membrane in a voltage-dependent manner. They had a low conductance to Rb and were blocked by Ba (1-100 microM) from the cytoplasmic side and tetraethylammonium (TEA) (0.2-1 mM) from the luminal side. Block by external TEA and small conductance to Rb were used to investigate the role of these channels in K transport by the isolated perfused rabbit CCT. Ba (2.5 mM), a well-studied blocker of apical K conductance in this segment, hyperpolarized the transepithelial voltage (VT) by 3.7 +/- 0.9 mV when added to the luminal solution of the perfused tubule. Addition of TEA (5 mM) to the luminal solution has no effect on VT. When Na transport was abolished by luminal amiloride, perfusion with 30 mM K (replacing Na) resulted in a lumen-negative VT (18-34 mV). Under these conditions, VT was reduced by 6.0 +/- 1.5 mV by 2.5 mM Ba, whereas TEA had no effect. Perfusion with 30 mM Rb (replacing Na) also caused a lumen-negative VT that was approximately 50% of that observed with 30 mM K. The apical K conductance of the perfused CCT appears to be insensitive to luminal TEA and only modestly selective for K over Rb. This conductance, at least under the conditions of our studies, is probably not mediated by the high conductance Ca-activated K channel.
Resetting of renal blood flow autoregulation in spontaneously hypertensive rats
Authors: Iversen B. M. , Sekse I. , Ofstad J.
Published: December 2017

Renal blood flow (RBF) autoregulation was examined in untreated 10- and 40-wk-old spontaneously hypertensive rats (SHR) [mean arterial pressure (MAP) 125 +/- 4 and 167 +/- 7 mmHg] and in captopril-treated (7 days) 10- and 40-wk-old SHR (88 +/- 7 and 112 +/- 5 mmHg). Age-matched Wistar-Kyoto rats (WKY) were used as controls (MAP 91 +/- 3 and 104 +/- 2 mmHg). The study was carried out in rats with and without acute uninephrectomy. In 10-wk-old acutely uninephrectomized animals, the lower pressure limit of autoregulation was 78 +/- 4 mmHg in WKY, 102 +/- 5 mmHg in SHR (P less than 0.02), and 78 +/- 7 mmHg in captopril-treated SHR (P greater than 0.10). The renal vascular resistance (RVR) was significantly elevated at the lower pressure limit of RBF autoregulation in untreated SHR (P less than 0.02) but became normal after treatment (P greater than 0.10). Neither uninephrectomy nor variation of RBF between different batches seemed to influence the lower pressure limit of RBF autoregulation. In 40-wk-old acutely nephrectomized animals, the lower pressure limit of RBF autoregulation in WKY was 85 +/- 4 mmHg, 128 +/- 3 mmHg in SHR (P less than 0.001), and 101 +/- 5 mmHg in captopril-treated SHR (P less than 0.01). RVR at the lower pressure limit was increased in untreated SHR (P less than 0.01), but fell to normal values during captopril treatment. Neither the uninephrectomy nor variation of RBF between different batches of rats seemed to influence the lower pressure limit of RBF autoregulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Conductive Na+ transport in an epithelial cell line (LLC-PK1) with characteristics of proximal tubular cells
Authors: Cantiello H. F. , Scott J. A. , Rabito C. A.
Published: December 2017

Na+ influx and efflux from confluent monolayers of an epithelial cell line with multiple differentiated characteristics of the straight segment of the renal proximal tubule were studied in the presence and absence of a pH gradient. The results show that Na+ influx in the absence of a pH gradient is inhibited by amiloride as well as by complete replacement of Cl- by an impermeable anion, such as isethionate. Dissipation of cell membrane potential by increasing the potassium concentration of the extracellular medium in the presence of valinomycin also inhibited Na+ influx, whereas sodium influx induced by an H+ gradient was not affected. Inhibition of Na+ influx by different maneuvers produced hyperpolarization of the plasma cell membrane, as would be expected if the sodium movement involved net displacement of charges. Calcium and other divalent and trivalent cations also inhibited Na+ influx measured in the absence of an H+ gradient. Na+ influx induced by a pH gradient, however, was not affected. Like the Na+-H+-exchange system, the conductive Na+ pathway is localized in the apical membrane of the epithelial cells. From these results, we conclude that at least a fraction of transepithelial Na+ transport in LLC-PK1 monolayers occurs through a simple rheogenic transport system.
Intrarenal generation of angiotensin II evaluated by an electrophysiological technique
Authors: Buhrle C. P. , Rosivall L. , Taugner R.
Published: December 2017

Angiotensin II (ANG II) reversibly depolarizes renin-containing juxtaglomerular epithelioid cells (JGECs) of the hydronephrotic mouse kidney afferent arteriole. This depolarizing response was utilized to assess changes in ANG II concentration in the vicinity of JGECs in order to test whether ANG II is generated from ANG I and artificial renin substrate (ARS) in this preparation. Depolarizations were also produced by the application of ANG I and ARS in the superfusing medium. These responses to ANG I and ARS were completely blocked by saralasin. Hence, our findings are indicative for an intrarenal, local generation of ANG II. As opposed to saralasin, several converting enzyme and renin inhibitors only diminished but generally did not abolish the actions of ANG I and ARS, respectively. These results suggest an alternative, nonrenin and non-converting enzyme-dependent pathway of ANG II generation in renal tissue.
Supersensitivity to NE alters renal function of chronically denervated rat kidneys
Authors: Krayacich J. , Kline R. L. , Mercer P. F.
Published: December 2017

The effect of norepinephrine (NE) infusion (10, 100, and 330 ng/min, iv) on renal blood flow (RBF), glomerular filtration rate (GFR), urine flow, and sodium excretion was studied during ganglionic blockade in Inactin-anesthetized Wistar rats with one kidney innervated and the contralateral kidney denervated 7-10 days before the experiment. During the NE infusions, steady-state mean arterial pressure was 73 +/- 3, 91 +/- 5, and 117 +/- 2 mmHg, whereas plasma NE concentration averaged 3.9 +/- 1.2, 26.4 +/- 3.2, and 78.1 +/- 4.8 pmol/ml, respectively. At the lowest dose, RBF and GFR were decreased significantly in both kidneys but were significantly lower in the denervated kidneys than in the innervated kidneys. Urine flow and total and fractional sodium excretion increased significantly from the innervated kidneys but not from the denervated kidneys during the 100 and 330 ng/min infusion of NE. When renal perfusion pressure was controlled at the level found after ganglionic blockade, RBF and GFR decreased significantly in both kidneys but to a greater extent in the denervated kidneys at all doses of NE. Urine flow and total and fractional sodium excretion decreased significantly from the denervated kidneys at all doses of NE but decreased from the innervated kidneys only at the highest dose. These results indicate that in chronically denervated kidneys both tubular and vascular responses to NE are altered. The data support the conclusion that denervation supersensitivity can significantly alter renal responses to increased plasma concentration of NE.
K-Cl transport systems in rabbit renal basolateral membrane vesicles
Authors: Eveloff J. , Warnock D. G.
Published: December 2017

The transport pathways for chloride in basolateral membrane vesicles from the rabbit renal cortex were investigated. 36Cl uptake was stimulated by the presence of potassium in the uptake media compared with sodium or N-methyl-D-glucamine. In addition, potassium (86Rb) uptake was stimulated more by chloride than by nitrate or gluconate. Neither of these processes was further stimulated by potassium gradients plus valinomycin, suggesting the presence of an electrically neutral K-Cl cotransport system. A magnesium-induced chloride conductance was also found in the basolateral membrane vesicles. In the absence of magnesium, the chloride conductance was low; valinomycin and an inwardly directed potassium gradient did not stimulate 36Cl uptake, anthracene-9-carboxylic acid did not inhibit 36Cl uptake, and valinomycin did not stimulate chloride-dependent 86Rb uptake. However, in the presence of 1 mM magnesium, opposite results were obtained; valinomycin and an inwardly directed potassium gradient stimulated 36Cl uptake, anthracene-9-carboxylic acid inhibited 36Cl uptake, and valinomycin stimulated chloride-dependent 86Rb uptake. Therefore, an electrically neutral K-Cl cotransport and magnesium-induced chloride conductance were found in renal cortical basolateral membrane vesicles prepared from the rabbit renal cortex.
Subcellular distribution of renal tripeptide-releasing exopeptidases active on collagen-like sequences
Authors: Andersen K. J. , McDonald J. K.
Published: December 2017

The rat kidney cortex was found to contain two N-terminal exopeptidases of the tripeptidyl peptidase (TPP) class. Each required a free N-terminus to catalyze the release of collagen-related (Gly-Pro-X) "triplets." In accordance with their apparent pH optima, activities were routinely determined fluorimetrically at pH 4.0 (TPP 4) and at pH 7.0 (TPP 7) on Gly-Pro-Met-2-naphthylamide. The specific activity in both the homogenate and the classical subfractions was much greater at pH 7 than at pH 4. Subfractionation of the microsomal fraction by equilibrium banding in sucrose did not separate the TPP 4 and TPP 7 activities. The banding density (1.18 g/ml) and the distribution patterns for TPP 7 in the microsomal subfractions, and also in the subfractions of the small lysosomes in the mitochondrial-lysosomal (ML) fraction, demonstrate that TPP 7 is associated with smooth membranes. The TPP 4 and TPP 7 activities were clearly separated during subfractionation of the ML fraction. Rate sedimentation demonstrated that TPP 4 was present in the large, fast-sedimenting lysosomes (protein droplets) and in a heterogeneous broad band of smaller lysosomes. Equilibrium banding of the small lysosomes gave two distinct TPP 4-containing populations at densities 1.20 and 1.235 g/ml. Notably, dipeptidyl peptidase II (DPP II) gave identical banding densities and showed distributions very similar to TPP 4.(ABSTRACT TRUNCATED AT 250 WORDS)
Selectivity of basolateral anion exchange in the acidification pathway of turtle bladder
Authors: Husted R. F. , Fischer J. L.
Published: December 2017

The turtle urinary bladder in vitro acidifies the solution bathing its luminal surface. Protons are actively extruded across the apical membrane by an H+-ATPase. Bicarbonate ion exits the cell across the basolateral membrane via a stilbene-sensitive, anion exchange for chloride. Chloride then exits the cell via a conductive pathway. The present studies were undertaken to define the specificity of the basolateral anion exchange mechanism for chloride. Turtle bladders were mounted on chambers in vitro, short-circuited, and treated with ouabain. The current remaining after inhibition of sodium transport was used to measure the acidification rate. Ion replacement studies with bromide, isethionate, sulfate, and nitrate indicated that only bromide supported acidification at rates comparable to chloride. In separate experiments, kinetic analysis of anion interaction with the exchanger indicates that maximal acidification rates decrease in the order: Cl greater than Br greater than SO4 greater than methyl sulfate = gluconate. The affinity of the exchanger decreases in the order: Cl greater than SO4 greater than Br greater than HCO3 greater than methylsulfate greater than gluconate. These selectivity sequences indicate "strong" interaction of the anions with the selectivity site. The differences in position of the polyatomic anions in the two sequences indicates that the "binding" site is accessible but that transport is limited by steric factors.
Aldosterone is a physiologically significant kaliuretic hormone
Authors: Adam W. R. , Ellis A. G. , Adams B. A.
Published: December 2017

To study the role of aldosterone in the short-term control of potassium excretion, rats were gavaged with a liquid diet containing 10-20% of their daily caloric and potassium intake, with a range of sodium intakes. Levels of (effective) aldosterone at the time of gavage were manipulated by administration of spironolactone, aldosterone, and adrenalectomy. Urinary sodium, potassium, and creatinine excretion were measured in conscious unrestrained rats for 2 h after the food load, and then blood was collected for measurement of plasma potassium, aldosterone, and renin activity. Potassium excretion was dependent on both dietary potassium and a minimum dietary sodium content. Potassium excretion was reduced by spironolactone and adrenalectomy and increased by acute aldosterone treatment in most dietary groups. These results strongly suggest that the ambient levels of aldosterone are important in determining potassium excretion following food ingestion. Plasma aldosterone was higher with the higher potassium and lower sodium content diets. Changes in plasma aldosterone, with variations in dietary potassium or sodium, suggest a role for aldosterone in subsequent potassium excretion.
High protein intake stimulates glomerular prostaglandin formation in remnant kidneys
Authors: Stahl R. A. , Kudelka S. , Helmchen U.
Published: December 2017

Reduction of renal mass in the rat results in an increased glomerular prostaglandin (PG) and thromboxane (TX) formation that modulates renal hemodynamics. To evaluate whether dietary protein intake could exert effects on renal PG and TX formation after reduction of approximately 70% of renal mass, rats with remnant kidneys were placed on either a high-protein (HP) or a low-protein (LP) diet. After 2 wk on the diet, proteinuria, glomerular filtration rate (GFR), urinary PGE2 excretion, and glomerular PGE2, 6-keto PGF1 alpha, and TxB2 biosynthesis were significantly greater in the rats on HP diets. Two-wk administration of the thromboxane synthesis inhibitor UK 38485 reduced renal TxB2 formation by approximately 70%. In addition, chronic UK 38485 treatment significantly inhibited papillary PGE2 production. Neither chronic nor bolus administration of UK 38485 had an effect on proteinuria or GFR in rats on HP diets. Chronic UK 38485 treatment, however, reduced GFR and proteinuria in rats on LP diets. The bolus administration of UK 38485 did not alter GFR in animals receiving a LP diet. The cyclooxygenase inhibitor indomethacin reduced GFR only in rats on HP diets. The data demonstrate that HP intake stimulates renal prostanoid formation. The increased prostaglandin formation on HP intake modulates GFR in these rats.
Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct [corrected and issued with original paging in Am J Physiol 1987 Aug;253(2 Pt 2)]
Authors: Star R. A. , Burg M. B. , Knepper M. A.
Published: December 2017

We measured bicarbonate, ammonia, and luminal pH in segments of the rabbit outer medullary collecting duct (OMCD) to determine the relationship between luminal pH and ammonia transport. Both the inner-stripe and outer-stripe portions of the OMCD absorbed bicarbonate at high rates. The outer stripe OMCD generated an acidic pH disequilibrium that was reversibly dissipated by exogenous luminal carbonic anhydrase. In contrast, the inner stripe OMCD did not generate a spontaneous pH disequilibrium unless perfused with the carbonic anhydrase inhibitor acetazolamide. Ammonia secretion was three times more rapid in the outer stripe OMCD than in the inner stripe OMCD. We conclude the following. 1) Both the inner-stripe and outer-stripe portions of the rabbit OMCD secrete protons at substantial rates. 2) Functional luminal carbonic anhydrase is present in the inner stripe OMCD but absent from the outer stripe OMCD. 3) Ammonia secretion occurs predominantly by NH3 diffusion in both portions. 4) The luminal pH disequilibrium, which is normally present in the outer stripe OMCD, enhances ammonia secretion.
Noninvasive Doppler assessment of human postprandial renal blood flow and cardiac output
Authors: Avasthi P. S. , Greene E. R. , Voyles W. F.
Published: December 2017

We compared the effects of protein, carbohydrate, or water ingestion on human renal blood flow (RBF) and cardiac output (CO). We validated and applied a noninvasive ultrasonic Doppler method to measure blood velocities and lumen diameters in the right renal artery and the ascending aorta of five healthy adults. From these measurements, we calculated the average RBF and CO over five cardiac cycles. Normalizing to body surface area, renal blood flow index to one kidney (RI) and cardiac index (CI) were calculated. The percentage of the CI distributed to a single kidney was determined as %CI = RI/CI. Subjects were studied randomly on three separate days after ingestion of each of the following equivolume (500 ml) meals: 1) 150 g protein, 30 g fat, and 30 g carbohydrate (P); 2) 150 g carbohydrate, 30 g fat, and 30 g protein (C); and 3) water. Data were obtained after 12 h of fasting and at 30, 60, 90, 120, 180, and 240 min postprandially. Analysis of covariance revealed significant (P less than 0.05) increases from fasting levels in postprandial RI at 90 to 240 min after P. Postprandial RI with P was significantly higher than with C at 180 and 240 min. Postprandial %CI with P and C decreased significantly from the fasting value at 30 to 180 min. Heart rate and mean arm cuff blood pressure did not change significantly with any diet. Results suggest that the protein-rich meal evokes a more sustained increase in postprandial RI than the carbohydrate rich meal. Despite the increase in postprandial RI, the percentage of cardiac output perfusing a kidney declines similarly with both diets.
In situ studies of distal convoluted tubule in rat. II. K secretion
Authors: Schnermann J. , Steipe B. , Briggs J. P.
Published: December 2017

Microperfusion and free-flow micropuncture studies were performed in anesthetized rats to compare the rates of K flux in early and late segments of the distal tubule. Early distal segments were located within the initial 40% of distal tubule length, and late distal segments were located within the terminal 35% of the distal tubule. In early distal segments of control rats, significant K secretion was observed at perfusion rates of 6 and 14 nl/min. In high-K rats significant K secretion was only observed at the lower perfusion rate. Late segments of control rats secreted 70.5 +/- 8.2 at the low flow rate and 139 +/- 18.9 pmol X min-1 X mm-1 at the high flow rate. In K-adapted rats, values were 134.4 +/- 30.2 and 178 +/- 29.3 pmol X min-1 X mm-1. During free flow, we observed a K flux in control rats of 11.0 +/- 9.4 pmol X min-1 X mm-1 (NS) in early segments and a K flux of 55 +/- 6.5 pmol X min-1 X mm-1 in late segments. In K-adapted rats, values were 18.3 +/- 6.7 (P less than 0.05) in early and 123 +/- 17.2 pmol X min-1 X mm-1 in late segments. The majority of our data suggests that the distal convoluted tubule secretes K at a low rate that is not influenced by flow rate or a high-K diet.
Lithium as a marker for proximal tubular delivery during low salt intake and diuretic infusion
Authors: Kirchner K. A.
Published: December 2017

Fractional lithium clearance (CLi/CIn), transit time occlusion time (e-TT/OT), and late proximal tubule fluid-to-plasma inulin ratio [1/(TF/P)In] determined by micropuncture were measured in the same kidney during 5-sec-butyl-5-ethyl-2-thiobarbituric acid (Inactin) anesthesia in rats fed either less than 2 mu eq sodium/g diet, rodent chow containing 20 mu eq sodium/g diet, or rodent chow and 0.5% NaCl to drink. Both CLi/CIn vs. e-TT/OT (r = 0.59) or 1(TF/P)In (r = 0.65) were linearly correlated at all sodium intakes. Quantitative estimates of proximal delivery by 1/(TF/P)In and e-TT/OT were similar (P = NS), whereas estimates from CLi/CIn were lower (P less than 0.05 or less) than the direct methods even when corrected for pars recta reabsorption. After acetazolamide or amiloride, but not furosemide, all methods for proximal delivery correlated quantitatively (P = NS) in sodium-restricted rats. Between amiloride and nondiuretic sodium-restricted rats, 1/(TF/P)In was not different. Proximal delivery estimated by CLi/CIn slightly (P = NS) underestimated direct measurements during 2% volume expansion [fractional sodium excretion (FeNa) 0.65 +/- 0.08%]. Thus, in the rat, CLi/CIn is not a quantitative estimate of proximal delivery if FeNa is less than 0.65% due to distal lithium reabsorption. CLi/CIn determined after amiloride may provide a correct estimate of proximal delivery during sodium restriction.
GFR regulation and flow-dependent electrophysiology of early distal tubule in Amphiuma
Authors: Persson B. E. , Marsh D. J.
Published: December 2017

Tubuloglomerular feedback (TGF) in mammals and amphibians senses flow-dependent concentration changes in tubular fluid of the distal tubule and signals to arterioles to initiate changes in glomerular filtration rate. The distal tubules and afferent arterioles are situated on the surface of the kidney of Amphiuma means. Micropuncture techniques were used to measure luminal and intracellular chloride concentrations and the associated electrical potential differences, while tubular perfusion rate was varied. Transepithelial potential difference (PDte) and basolateral potential difference (PDbl) became more positive at increased tubular flow rates. Intratubular and intracellular chloride concentrations also increased significantly with perfusion rate. Single-nephron glomerular filtration rate decreased when perfusion rate was increased but this response was eliminated by the inclusion of furosemide in the perfusion solution; the drug also inhibited the flow dependence of PDte. The results suggest that local changes in PD and Cl- activity result from flow-dependent changes in the rate of hypertonic NaCl transport propagated along the length of the perfused segment; they establish a correlation between the rate of transport and the magnitude of the TGF inhibition; and, because transport and TGF can be jointly inhibited, they suggest a causal link between the two.
Bicarbonate transport by initial collecting tubule of aquatic- and land-phase amphibia
Authors: Yucha C. B. , Stoner L. C.
Published: December 2017

The rate of bicarbonate reabsorption (JHCO3) by in vitro initial collecting tubules (ICT) from aquatic- and land-phase Ambystoma tigrinum was measured. These animals intrinsically have different levels of plasma bicarbonate, 17.6 and 27.1 mM, respectively. ICT from both phases reabsorbed bicarbonate at 11 pmol X mm-1 X min-1 when perfused in solutions equilibrated with 3% CO2. The induction of metabolic acidosis or alkalosis had no effect on JHCO3 by in vitro ICT. JHCO3 was abolished when ICT from aquatic animals were perfused with solutions equilibrated with 1% CO2 and returned toward the control value when 3% CO2 was reintroduced. The effect of plasma CO2 partial pressure on JHCO3 of the ICT may explain, at least in part, the observed difference in plasma bicarbonate of the aquatic- and land-phase animals. JHCO3 was reduced to 22% of control with amiloride and to 42% of control when a Na+-free perfusate was used, but was insensitive to ethoxzolamide. These data are consistent with the presence of a sodium-proton exchanger on the apical membrane and a carbonic anhydrase-independent mechanism of H+ secretion.
Anion exchange pathways for Cl- transport in rabbit renal microvillus membranes
Authors: Karniski L. P. , Aronson P. S.
Published: December 2017

We evaluated the mechanisms of chloride transport in microvillus membrane vesicles isolated from the rabbit renal cortex. The presence of Cl-formate exchange was confirmed. Outward gradients of oxaloacetate, HCO3, acetate, lactate, succinate, sulfate, and p-aminohippurate (PAH) stimulated the rate of Cl uptake minimally (less than 25%) or not at all. However, an outward gradient of oxalate stimulated Cl uptake by 70%, and an outward Cl gradient induced uphill oxalate uptake, indicating Cl-oxalate exchange. Moreover, an outward formate gradient induced uphill oxalate uptake, indicating formate-oxalate exchange. Studies of inhibitor and substrate specificity indicated the probable operation of at least two separate anion exchangers in mediating Cl transport. The Cl-formate exchanger accepted Cl and formate as substrates, had little or no affinity for oxalate, was sensitive to inhibition by furosemide, and was less sensitive to inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The Cl (formate)-oxalate exchanger also accepted Cl and formate as substrates but had high affinity for oxalate, was highly sensitive to inhibition by DIDS, and was less sensitive to inhibition by furosemide. The Cl-formate exchanger was electroneutral, whereas the Cl (formate)-oxalate exchanger was electrogenic. We conclude that at least two separate anion exchangers mediating Cl transport are present on the luminal membrane of the rabbit proximal tubule cell. These exchangers may play important roles in mediating transtubular Cl and oxalate transport in this nephron segment.