bluuebunny/crossref_metadata_2025 huggingface dataset:
Vascular muscle cell depolarization and activation in renal arteries on elevation of transmural pressure
Authors: Harder D. R. , Gilbert R. , Lombard J. H.
Published: December 2017

The goal of this study was to define some of the cellular and ionic mechanisms of smooth muscle cell activation in dog renal arteries exposed to physiological levels of transmural pressure. Isolated interlobular arteries were cannulated and connected to a pressure reservoir to allow manipulation of transmural pressure in 20-mmHg increment steps from 20 to 120 mmHg. As transmural pressure was increased, vascular smooth muscle exhibited a linear depolarization from an average resting potential of -57+/- 2 mV at 20 mmHg to -38+/- 2.4 mV at 120 mmHg. Spontaneous action potentials could often be recorded at pressures greater than 80 mmHg. These appeared to occur primarily at bifurcation points of branching arteries. Vascular smooth muscle depolarization and action potentials occurring in response to increases in transmural pressure were associated with a maintenance of internal diameter of the vessel segments despite increases in transmural pressure in the range between 60 and 120 mmHg. The “pressure-induced” activation of vascular smooth muscle contraction and spontaneous action potentials of small renal arteries at higher transmural pressures were blocked on Ca2+ channel inhibition with verapamil (10(-6) M). These data document a membrane ionic mechanism (probably increased Ca2+ influx) for pressure-induced myogenic activation of isolated renal arteries. It is interesting that the contraction of these vessels occurs over the pressure range in which autoregulation of renal blood flow normally occurs. The physiological significance of these responses needs to be determined.
Renal effects of aprotinin after 24 hours of unilateral ureteral obstruction
Authors: Yarger W. E. , Newman W. J. , Klotman P. E.
Published: December 2017

We have previously demonstrated that, after the release of 24-h unilateral ureteral obstruction (UUO), glomerular filtration rate (GFR), and renal blood flow (RBF) are reduced because of increased production of the potent vasoconstrictors thromboxane A2 (TxA2) and angiotensin II (ANG II). Captopril, which blocks ANG II production, increases GFR and RBF. Sequential administration of aprotinin, a kallikrein inhibitor, has an additive effect to further decrease renal vasoconstriction, even though kinins are generally thought to be vasodilators. Therefore, we assessed mechanisms by which aprotinin might improve renal function of previously obstructed anesthetized rats. When given alone to UUO rats, aprotinin improved renal hemodynamics. Since kinins stimulate TxA2 production by UUO kidneys perfused in vitro, our data suggest that aprotinin improved postobstructive function by decreasing kinin-stimulated TxA2 production, although this may not be its only effect. Aprotinin also improved postobstructive function, even if TxA2 formation was blocked with indomethacin. But when both ANG II and TxA2 formation were blocked by the simultaneous administration of captopril and indomethacin, aprotinin had no effect. This suggests that aprotinin may also affect ANG II formation. These pharmacological effects of aprotinin suggest that the kallikrein-kinin system may also contribute to postobstructive renal vasoconstriction by stimulating the production of both vasoconstrictor eicosanoids and ANG II.
Control of renin release by dietary NaCl in the rat
Authors: Welch W. J. , Ott C. E. , Lorenz J. N. , Kotchen T. A.
Published: December 2017

The purpose of the present study is to determine whether changes of plasma renin activity (PRA) induced by dietary NaCl are mediated by a renal tubular mechanism or by a neural mechanism. Male Sprague-Dawley rats were placed on low-, normal-, or high-NaCl diets for 1 wk (n = 8 for each group). There were no group differences of glomerular filtration rate (GFR), renal plasma flow, Na+ or Cl- delivery to the loop, Na+ or Cl- reabsorption in the loop, Na+ or Cl- concentration in early distal tubular fluid, or Na+ or Cl- delivery to the early distal tubule. PRA of rats on normal NaCl (4.8 ng.ml-1.h-1 +/- 0.8) was greater (P less than 0.05) than that of rats on high NaCl (3.3 +/- 0.4) and less (P less than 0.05) than that of animals on low NaCl (9.1 +/- 1.8). To determine whether alterations of PRA by dietary NaCl might be related to low-pressure baroreceptors with vagal afferents, animals were bilaterally vagotomized after micropuncture. Forty-five minutes after vagotomy, PRA increased (P less than 0.05) on each of the diets, however, after vagotomy mean PRA in animals fed normal (10.9 +/- 1.8) and low NaCl (13.2 +/- 2.2) did not differ. Thus our results do not support the hypothesis that suppression of PRA by dietary NaCl loading is related to a renal tubular mechanism. A vagally mediated mechanism may contribute to renin suppression by dietary NaCl.
Luminal and basolateral uptake of insulin in isolated, perfused, proximal tubules
Authors: Nielsen S. , Nielsen J. T. , Christensen E. I.
Published: December 2017

The present study was performed to quantitate and compare the luminal and the peritubular uptake of 125I-labeled insulin in isolated, perfused, proximal tubules from rabbit kidneys. 125I-insulin was added in physiological concentrations of 3.0-7.0 ng/ml or 59.0-89.5 ng/ml (high insulin concentrations) to either the perfusate or the bath fluid for 30 min. The luminal uptake in 30 min averaged 0.76 pg/mm at physiological concentrations and 18.0 pg/mm at high insulin concentrations. About 15-41% of the absorbed insulin was digested and less than 5% was transported from the lumen to the peritubular space as intact insulin. The peritubular binding/uptake of 125I-insulin at physiological and high concentrations in the bath was 0.136 and 0.318 pg, respectively. Addition of excess unlabeled insulin (10(-5) M) to the bath produced significant inhibition of binding (53.7%) at 7.0 ng/ml, but no inhibition at 89.5 ng/ml labeled insulin in the bath. This indicates that insulin is bound/absorbed at the basolateral membranes both by a saturable specific mechanism and a nonspecific, nonsaturable mechanism. The basolateral absorption constituted 15.2 and 1.8% of the total tubular extraction of insulin at physiological and high insulin concentrations, respectively. Electron microscope autoradiography showed that, after luminal as well as basolateral endocytosis, insulin was exclusively accumulated in endocytic vacuoles and lysosomes.
Asymmetric affinity of Na+-H+ antiporter for Na+ at the cytoplasmic versus external transport site
Authors: Goldfarb D. , Nord E. P.
Published: December 2017

The affinity for Na+ of the cytoplasmic vs. external transport site of the amiloride-sensitive Na+-H+ antiporter was studied in confluent cultures of MDCK cells. Na+-H+ antiport activity was fluorometrically determined by monitoring changes in intracellular pH (pHi) using the pH-sensitive fluorescent probe, BCECF. Na+-dependent H+ fluxes were studied both in the functionally operative (H+ efflux/Na+ influx) and reverse (H+ influx/Na+ efflux) mode of antiport activity, under pH equilibrium, but Na+-gradient conditions. Thus the driving force for antiport activity was solely dependent on the transmembrane Na+ gradient. Independent experiments established that pHi and intracellular Na+ [Na+i] had been set at the desired values before the initiation of a particular experiment. Under conditions of pHi = pHo = 7.0, [Na+i] = 0 mM and varying extracellular Na+ concentration [Na+o], the apparent affinity for Na+ (KtNa) for the external transport site was 24 +/- 3 mM. When antiport activity was measured in the reverse mode of operation, but under identical pH conditions, KtNa at the internal site was 7 +/- 1 mM. When ambient pH was elevated to 7.5, KtNa at the internal site was 14 +/- 1 mM. Maximum H+ flux (JmaxH+) for the antiporter under all three conditions was not significantly different. In summary, the Na+-H+ antiporter displays asymmetric affinity for Na+ at the internal vs. external transport site. Under pH equilibrium conditions, the affinity of the Na+-H+ antiporter for Na+ is three- to four-fold greater at the internal vs. external locus, and the affinity for Na+ at the internal site is enhanced by lower pHi. The close similarity between values for KtNa (inside) and reported values for intracellular Na+ concentration suggests that regulation of the Na+-H+ antiporter may be affected by changes in intracellular Na+ concentration.
Ultrastructural changes in isolated perfused proximal tubules during osmotic water flow
Authors: Maunsbach A. B. , Tripathi S. , Boulpaep E. L.
Published: December 2017

Steady-state effects of osmotic gradients on extracellular spaces and cell volumes were studied by ultrastructural morphometry in isolated perfused Ambystoma proximal tubules. Solute clamping, high-resolution pressure and flow control of lumen and bath solutions were all ascertained before and during fixation. Isosmotic removal of organic substrates in the lumen reversibly abolished transport, as confirmed by transepithelial potential decrease from -4.7 +/- 0.5 to -0.5 +/- 0.2 mV (n = 8) but had no effect on ultrastructural parameters. The walls of the extracellular spaces are therefore not deformed by spontaneous solute-coupled water transport. A hyperosmolar lumen generated a streaming potential of -1.56 +/- 0.15 mV (n = 8), reduced cell volume to 65%, reduced lateral intercellular space (LIS) volume to 20%, and LIS volume density to 29% of control without significant effects on the volume of the basal extracellular labyrinth (BEL). A hyperosmolar bath generated a streaming potential of +1.96 +/- 0.30 mV (n = 7), reduced cell volume to 68%, and increased LIS volume density to 236% of control. BEL volume was 55% larger during lumen-to-bath flow than during bath-to-lumen flow. Because cell volume reduction is very similar for both directions of osmotic water flow, the oppositely directed volume changes in the extracellular spaces are secondary to transepithelial water flow. The greater change in volume of LIS compared with BEL indicates that the outermost parts of the LIS are more resistive to transepithelial water flow than the slitlike communications of the BEL with the peritubular space.
Effect of acute respiratory acidosis on two populations of intercalated cells in rat cortical collecting duct
Authors: Verlander J. W. , Madsen K. M. , Tisher C. C.
Published: December 2017

Recent studies suggest the presence of two populations of intercalated cells in the rabbit cortical collecting duct (CCD), one involved with hydrogen ion secretion and another that may play a role in bicarbonate secretion. The purpose of this study was to determine whether two populations of intercalated cells are present in the rat CCD and to establish their response to acute respiratory acidosis. Rats were studied during normal acid-base conditions and after 4-5 h of respiratory acidosis. In all animals light microscopy and transmission and scanning electron microscopy revealed two configurations of intercalated cells, type A with an extensive apical tubulovesicular membrane compartment and prominent surface microprojections and type B with a well-developed vesicular compartment and short sparse surface microprojections. By transmission electron microscopy, studs were present on the cytoplasmic face of the apical plasmalemma and tubulovesicular profiles of A cells. In respiratory acidosis there was a striking increase in apical microprojections and in the surface density of the apical membrane of type A cells similar to the response observed previously in intercalated cells in the outer medullary collecting duct (OMCD) studied under the same physiological conditions. No changes were observed in type B cells. Scanning electron microscopy revealed no change in the relative number of type A and type B cells in respiratory acidosis. We conclude that two distinct populations of intercalated cells exist in the rat CCD: type A, which resembles the intercalated cells in the OMCD, and type B. The response of type A cells to acute respiratory acidosis and the similarity between these cells and intercalated cells in the OMCD, which are believed to secrete hydrogen ion, suggest that the type A cells are involved in hydrogen ion secretion in the CCD.
Effect of pH on Cl- transport in TAL of Henle's loop
Authors: Kondo Y. , Yoshitomi K. , Imai M.
Published: December 2017

To further characterize the mechanism of Cl- transport across the hamster thin ascending limb (TAL) of Henle's loop, we examined effects of pH on Cl- permeability as determined by either the choline chloride diffusion voltage or the lumen-to-bath 36Cl flux in the isolated segments perfused in vitro. When pH of the bathing fluid or the perfusate was reduced from 7.4 to 5.8, the Cl(-)-Na+ permeability ratio (PCl/PNa) was reduced from 2.77 +/- 0.21 to 0.48 +/- 0.02 (n = 7, P less than 0.01) or from 2.55 +/- 0.15 to 0.81 +/- 0.11 (n = 6, P less than 0.01), respectively. At 37 degrees C, when the pH of the bathing fluid was reduced from 7.4 to 6.2, the lumen-to-bath flux coefficient for 36Cl (X10(-7) cm2/s) was reduced from 84.8 +/- 7.5 to 20.4 +/- 3.2 (n = 7, P less than 0.01), whereas the value for 22Na was unchanged (27.3 +/- 2.9 vs. 25.3 +/- 2.5, n = 5). From the pH titration curves for PCl/PNa, pKa values for proton binding were 6.31 and 5.78, and Hill's coefficients were 2.1 and 2.3 on the basolateral side and on the luminal side, respectively. Alkalinization had little or no effect on the Cl- permeability. At room temperature, the acid pH did not affect the Cl- permeability. Intracellular acidification with o-nitrophenylacetate also decreased the Cl- permeability.(ABSTRACT TRUNCATED AT 250 WORDS)
Disequilibrium pH and ammonia transport in isolated perfused cortical collecting ducts
Authors: Star R. A. , Kurtz I. , Mejia R. , Burg M. B. , Knepper M. A.
Published: December 2017

The present study was carried out to test directly whether isolated perfused rabbit cortical collecting ducts (CCDs) spontaneously generate a luminal disequilibrium pH. We determined disequilibrium pH as the difference between 1) the actual luminal pH measured by perfusing the lumen with a membrane-impermeant pH-sensitive dye [1,4-dihydroxyphthalonitrile (1,4-DHPN)] and 2) equilibrium pH calculated from the measured total CO2 concentration in fluid collected at the end of the tubule. When the peritubular bath and perfusate had the same composition, a statistically significant acidic disequilibrium pH was found (mean -0.14 units). To determine whether the disequilibrium pH is due to an absolute lack of luminal carbonic anhydrase, we measured the effective rate constant for carbonic acid dehydration in the lumen (k-1). To do this, a lumen-to-bath NH3 concentration gradient was imposed, and the luminal pH was measured along the tubule with 1,4-DHPN. NH3 absorption caused a luminal disequilibrium pH (due to dissociation of NH+4 to NH3 and H+), whose profile along the lumen is dependent on k-1 and NH3 permeability (PNH3). PNH3 and k-1 were estimated from the luminal pH profiles using a mathematical model of proton and buffer transport. The measured k-1 (37 s-1) is within the reported range of values for uncatalyzed H2CO3 dehydration. Calculations demonstrate that the measured PNH3 (2 X 10(-3) cm/s) is high enough and the measured k-1 is low enough to explain ammonia secretion rates seen in previous studies. We conclude that proton secretion in the CCD generates an acidic luminal disequilibrium pH, associated with an absolute lack of luminal carbonic anhydrase, which enhances the net rate of NH3 secretion.
Single-channel analysis of a K channel at basolateral membrane of rabbit proximal convoluted tubule
Authors: Parent L. , Cardinal J. , Sauve R.
Published: December 2017

The basolateral membrane of the rabbit proximal convoluted tubule (PCT) is known to be largely permeable to K ions. The patch-clamp technique was used to investigate the molecular basis of this K permeability. At room temperature and with a high-K solution (127 mM) in both the bathing medium and the patch pipette, current jumps associated with an inward-rectifying channel could be detected in every active cell-attached experiment. When the K concentration in the pipette was changed from 200 to 5 mM KCl (NaCl replacement), the single-channel conductance for inward currents changed from 54 to 10 pS. The observed shift in the zero current potential measured as a function of the patch pipette K concentration could be fitted using the Goldman-Hodgkin-Katz equation with a permeability ratio PNa/PK = 0.06. The channel was found to be moderately voltage dependent (e-fold per 56 mV depolarization). For instance, the open-channel probability (Po) increased from 0.06 to 0.16 following a membrane depolarization from -50 to +50 mV. A time interval distribution analysis showed for the open state a dominant single time constant of 14 and 10 ms at 50 and -50 mV, respectively. Two time constants equal to 1 (flickering) and 26 ms at +50 mV and to 0.6 and 300 ms at -50 mV were obtained for the closed-state interval distribution. Based on this analysis, it was concluded that the decrease of Po at negative potentials was due more to the appearance of prolonged silent periods than from a change in the channel mean open time.
Plasma AVP and renal concentrating defect in chloride depletion metabolic alkalosis
Authors: Peterson L. N. , Sztorc D. , Jamshaid A. , Kucharczyk J. , Bichet D. , Levine D. Z.
Published: December 2017

These studies were undertaken to determine the effect of chronic chloride depletion metabolic alkalosis (Cl-DEP-MALK) on water intake, plasma arginine vasopressin (AVP) levels, and renal concentrating ability. Cl-DEP-MALK was induced by feeding a chloride-free diet to rats subjected to gastric drainage and to dogs treated with furosemide. All of the animals developed a urine concentrating defect, polydipsia, and a persistent reduction in plasma osmolality. However, AVP release was not suppressed. The results of osmotic loading experiments in dogs analyzed using either linear or log-linear models have shown that chronic Cl-DEP-MALK significantly alters the relation between plasma osmolality and plasma AVP. In the classic linear analysis the results suggest that Cl-DEP-MALK reduces the plasma osmolality at which plasma AVP can be detected, i.e., reduced “threshold,” and increases the slope of the plasma osmolality-to-plasma AVP relation nearly twofold, i.e., increased “sensitivity.” Finally, we provide evidence that the concentrating defect is not related to high water turnover or deficient endogenous AVP and is therefore nephrogenic.
Glucocorticoids have a different action than aldosterone on target tissue
Authors: Halevy J. , Boulpaep E. L. , Budinger M. E. , Binder H. J. , Hayslett J. P.
Published: December 2017

Studies were performed, using a synthetic glucocorticoid, RU 28362, that has negligible binding to aldosterone receptors, to examine whether the effect of glucocorticoids on the electrical properties of rat distal colon involves a specific mechanism or crossover binding to aldosterone receptor sites. Compared with control, RU 28362, in a dose of 70 micrograms.100 g body wt-1.day-1, increased transepithelial potential differences (VT) twofold and the equivalent short-circuit current (ISC) threefold; epithelial resistance (RT) was reduced 25%. These changes were qualitatively similar to, but less than, the changes induced by the same dose of aldosterone. The effects of dexamethasone in the same dose were indistinguishable from the changes caused by aldosterone. The results of cell-impalement studies corresponded to whole epithelial changes; RU 28362 induced a small increase in basolateral potential difference, from -43 +/- 2 to -45 +/- 1 mV, and a fall in apical potential difference, from 40 +/- 2 to 36 +/- 1 mV, but these effects on cell membrane voltage were less than caused by either aldosterone or dexamethasone. In contrast to the marked inhibitory action of amiloride to reduce VT in aldosterone- and dexamethasone-treated animals, this sodium channel blocker had no effect on VT in RU 28362-treated animals. Similarly, while spironolactone caused marked inhibition of the changes in VT, RT, and ISC induced by aldosterone, the inhibitory action on tissue from RU 28362-treated animals was slight or absent. These results suggest that glucocorticoids have a specific aldosterone receptor-independent action on the electrical properties of the large intestine.
A highly sensitive radioreceptor assay for atrial natriuretic peptide in rat plasma
Authors: Ballermann B. J.
Published: December 2017

To enable serial measurements of plasma atrial natriuretic peptide (ANP) concentrations in the rat, a microradioreceptor assay (RRA) for this hormone was developed. Glomerular microsomes bearing ANP receptors were used to bind ANP. The smallest quantity of ANP detectable by this method was 0.2 fmol/sample. By contrast, a radioimmunoassay for ANP was sensitive to 2.4 fmol/sample. The intra- and interassay coefficients of variation for the RRA were 4.1 and 11.6%, respectively. Recovery of 10, 20, 50, and 100 pM synthetic ANP added to unextracted rat plasma was essentially 100%. Biologically inactive, synthetic amino- and carboxy-terminal ANP fragments added to rat plasma were not detected. Plasma ANP was stable when measured four consecutive times at 90-min intervals in 10 fasting rats. In a separate group of rats, fasting plasma ANP levels averaged 34 +/- 3 and rose to 57 +/- 5 pM in the postprandial state (P less than 0.001), whereas levels in fasting time controls remained constant. It is concluded that the RRA for ANP described here detects ANP in microliter quantities of unextracted rat plasma. Thus serial measurements of ANP concentrations can be undertaken in rats without inducing major changes in the volume status.
Proton-translocating ATPase from bovine kidney medulla: partial purification and reconstitution
Authors: Gluck S. , Caldwell J.
Published: December 2017

The proton-translocating ATPase that is responsible both for urinary and vacuolar acidification was partially purified from bovine kidney medulla microsomes. ATPase activity was purified to a maximum specific activity of 1.7 mumol.min-1.mg prot-1 and was inhibited completely by N-ethylmaleimide. The relative molecular weight (Mr) of the intact protein estimated by high-pressure size-exclusion liquid chromatography was 586,000. Nondenaturing gels of the isolated enzyme revealed two protein bands at MrS of 551,000 and 523,000. Sodium dodecyl sulfate-gel electrophoresis of the isolated H+-ATPase revealed component subunits at MrS of 70,000, 56,000, 45,000, 42,000, 38,000, 31,000, 15,000, 14,000, and 12,000. The properties of the isolated H+-ATPase and of microsomal ATP-dependent proton transport correlated closely. The isolated H+-ATPase was reconstituted into phospholipid liposomes and demonstrated N-ethylmaleimide-inhibitable ATP-dependent potential generation, consistent with electrogenic proton transport. In overall structure, the enzyme appears to be a new type of H+-ATPase with several features of the F0F1 class of ion-translocating ATPases but is immunologically and structurally different from the mitochondrial F1-ATPase.
An ATP-inhibited soluble 5'-nucleotidase of rat kidney
Authors: Le Hir M. , Dubach U. C.
Published: December 2017

Hydrolysis of 5'-AMP by 5'-nucleotidase is a possible source of adenosine in the kidney. A renal membrane-bound ecto-5'-nucleotidase has been previously described. The present study deals with the catalytic properties of a 5'-AMP phosphohydrolase partially purified from high-speed supernatants of rat kidney homogenates. It exhibits phosphatase activity toward 5'-AMP, 5'-IMP, and 5'-GMP, but not toward 2'- and 3'-AMP and corresponds therefore to a 5'-nucleotidase. The hydrolysis of 5'-AMP by the soluble 5'-nucleotidase requires divalent cations. Maximal activity is reached with 10 microM of either Mn2+ or Co2+, whereas half-maximal activity is obtained with approximately 400 microM Mg2+. The soluble 5'-nucleotidase exhibits Michaelis-Menten kinetics with a Km of 9.5 microM for 5'-AMP. In the presence of 1 mM of free Mg2+, physiological concentrations of ATP provoke an increase of the Km for 5'-AMP and a decrease of Vmax. An increase of the pH of 0.4 units in the pH range 6.4-7.4 roughly doubles the rate of hydrolysis of 5'-AMP. The effects of ATP and of the pH are compatible with a role of the renal soluble 5'-nucleotidase in the hydrolysis of 5'-AMP and in the production of adenosine during hypoxia.
Indirect evidence of glomerular/tubular mixed-type postexercise proteinuria in healthy humans
Authors: Poortmans J. R. , Brauman H. , Staroukine M. , Verniory A. , Decaestecker C. , Leclercq R.
Published: December 2017

Hypothetical mechanisms have been postulated to explain the presence of proteins in urine after severe exercise. Recently, it has been shown that several amino acids inhibit tubular protein reabsorption. Seven healthy men, hyperhydrated, were studied during a 2-min bicycle exercise at supramaximal load. The subjects were tested without or with lysine perfusion (0.4 g/kg body wt iv). In both testing conditions, blood lactate increased to 13.8 mmol/l. Total protein urinary excretion increased to 1.10 and 1.67 mg/min, without and with lysine perfusion, compared with 79 micrograms/min at rest. In the meantime, albumin excretion increased 48- and 74-fold, respectively, while beta 2-microglobulin excretion increased 97- and 1,043-fold compared with basal values. The renal clearance of albumin increased to 8.4 microliters/min without lysine and to 12.0 microliters/min with lysine perfusion (rest 0.18). beta 2-Microglobulin clearance increased to 10.0 and 39.3 ml/min, respectively (rest 0.05). These data clearly demonstrate that postexercise proteinuria is of mixed type after exhaustive short-term exertion. Both increased glomerular permeability and partial tubular reabsorption inhibition to proteins appear to be involved.
Intrarenal renin-angiotensin system modulates glomerular angiotensin receptors in the rat
Authors: Wilkes B. M. , Pion I. , Sollott S. , Michaels S. , Kiesel G.
Published: December 2017

The aim of this study was to test the hypothesis that the intrarenal renin-angiotensin system (RAS) modulates glomerular angiotensin II (ANG II) receptors. In one protocol ANG II receptors were measured 7 days after unilateral denervation of the left kidney in rats. There were 50% more receptors in the glomeruli from denervated compared with innervated kidneys (right, 1,037 +/- 108 vs. left, 1,556 +/- 143 fmol/mg; P less than 0.01), which was associated with a 63% reduction (P less than 0.01) in left renal vein renin. The differences in ANG II receptors between the left and right kidneys were no longer present when angiotensin-converting enzyme was inhibited with enalapril or when pharmacological amounts of ANG II (50 ng/min) were infused. In a second protocol, renal cortical renin content was raised in the left kidney by placing a 0.20-mm clip on the left renal artery (two-kidney, one-clip Goldblatt model). At 7 days, glomerular ANG II receptors were reduced by 72.3% in the clipped compared with the contralateral kidneys (right, 1,232 +/- 105 vs. left, 341 +/- 170 fmol/mg; P less than 0.01). The differences in ANG II receptors were no longer present after enalapril treatment. Pharmacological maneuvers that either blocked ANG II formation or increased circulating ANG II resulted in an equal number of ANG II receptors in the right and left kidneys. The data indicate that the intrarenal RAS modulates the density of glomerular ANG II receptors and is a more important receptor modulator than plasma ANG II.
Isoproterenol and cyclic AMP increase intracellular free [Ca] in MDCK cells
Authors: Chase H. S. , Wong S. M.
Published: December 2017

We examined the relationship between cyclic AMP and the intracellular free calcium concentration ([Ca]i) in MDCK cells, a hormonally responsive and chloride-secreting cell line. We measured [Ca]i using the calcium-sensitive dye fura-2, fluorescence microscopy, and a silicon intensifier target camera to amplify the signal. Isoproterenol, known to stimulate chloride transport via cyclic AMP, increased [Ca]i from 112 +/- 17 to 373 +/- 53 nM. The rise appeared due to an increase in cyclic AMP: isobutylmethylxanthine enhanced the effect of a submaximal dose of isoproterenol on [Ca]i, the cyclic AMP analogue 8-bromo-cyclic AMP caused [Ca]i to increase from 100 +/- 8 to 278 +/- 40 nM, and direct activation of adenylate cyclase with forskolin increased [Ca]i from 192 +/- 29 to 279 +/- 35 nM. The rise in [Ca]i after cyclic AMP may be due to an influx of calcium from the outside: the cyclic AMP-induced increase in [Ca]i was prevented either by lowering extracellular [Ca] or by addition of 1 mM lanthanum. The mechanism by which calcium enters the cell may not be a calcium channel because neither verapamil nor nitrendipine prevented cyclic AMP from increasing [Ca]i. Cyclic AMP also does not appear to act directly on sodium-calcium exchange. [Ca]i increased as well in low [Na] as in high [Na] following addition of the nucleotide. Thus, isoproterenol, acting through an increase in [cyclic AMP] causes an increase in [Ca]i in MDCK cells. The source and route of entry of calcium into the cytoplasm remain uncertain.
Prostaglandin blockade blunts the natriuresis of elevated renal interstitial hydrostatic pressure
Authors: Pawlowska D. , Haas J. A. , Granger J. P. , Romero J. C. , Knox F. G.
Published: December 2017

Previous studies have shown that renal interstitial volume expansion (RIVE) increases renal interstitial hydrostatic pressure and urinary sodium excretion. In the present study we investigated whether blockade of prostaglandin synthesis inhibits the increase in fractional sodium excretion induced by RIVE. Expansion of the renal interstitial volume was achieved by injecting 50 microliters of 2.5% albumin solution into a polyethylene matrix chronically implanted in the left kidney. Fractional sodium excretion (FENa), renal interstitial hydrostatic pressure (PI), and urinary prostaglandin excretion (UPGE2) were measured before and after RIVE in eight control, seven meclofenamate-treated, and eight indomethacin-treated rats. RIVE in the control animals resulted in significant increases in PI (delta + 4.2 +/- 0.8 mmHg), in FENa (delta + 1.02 +/- 0.27%), and in UPGE2 (% delta + 150 +/- 38%) without significant changes in glomerular filtration rate. Inhibition of prostaglandin synthesis with meclofenamate or indomethacin attenuated the natriuretic response and blocked the increase in UPGE2 associated with RIVE. In summary, direct increases in renal interstitial hydrostatic pressure increase UPGE2 and urinary sodium excretion. This natriuretic response is markedly diminished by inhibition of prostaglandin synthesis. These studies suggest that prostaglandin synthesis may have an important role in mediating the natriuretic effect of increased renal interstitial hydrostatic pressure during renal interstitial volume expansion.
Increased vascular response to calcium channel agonist by Dahl S rat kidney
Authors: Steele T. H. , Challoner-Hue L.
Published: December 2017

We examined responses to the calcium channel agonist, BAY-K 8644, of isolated perfused kidneys from Dahl salt-sensitive (DS) and -resistant (DR) rats that had been stabilized on high (HI) and low (LO) NaCl intakes. Mean arterial pressures of DS/HI rats exceeded those of the other three groups. BAY-K 8644 significantly increased the renal vascular resistance (RVR) of DS/HI and DS/LO kidneys, by 38 and 12%, respectively, but did not increase RVR of DR/HI or DR/LO kidneys significantly (6 and 2%, respectively). Increases in RVR and decreases in glomerular filtration rate of DS/HI kidneys exceeded those of DR/HI kidneys. Increases in the RVR of DS/LO kidneys exceeded those of DR/LO kidneys. Experiments utilizing the separate calcium channel agonist and antagonist enantiomers of BAY-K 8644 corroborated these findings, but at lower concentrations. “Chemical sympathectomy” with 6-hydroxydopamine increased the reactivity of kidneys from only high-NaCl animals to BAY-K 8644 without regard to Dahl S or R status. In conclusion, the DS kidney vasculature manifests an increase in responsiveness to this calcium channel agonist, independently of antecedent NaCl loading or high blood pressure. However, a high antecedent salt intake or hypertension enhances vascular responsiveness of the DS kidney to BAY-K 8644.
Time-dependent aldosterone metabolism in toad urinary bladder
Authors: Brem A. S. , Pacholski M. , Morris D. J.
Published: December 2017

Aldosterone (Aldo) metabolism was examined in the toad bladder. Bladders were incubated with [3H]aldosterone (10(-7) M) for 5 h, 1 h, or 10 min. Tissues were analyzed for metabolites using high-pressure liquid chromatography (HPLC). In separate experiments, Na+ transport was assessed by the short-circuit current (SCC) technique. Following a 5-h tissue incubation, about 25% of the [3H]-aldosterone was converted into metabolites including a polar monosulfate metabolite, 20 beta-dihydroaldo (20 beta-DHAldo), small quantities of 5 beta-reduced products, and a variety of 5 alpha-reduced Aldo products including 5 alpha-DHAldo, 3 alpha,5 alpha-tetrahydroaldo (3 alpha,5 alpha-THAldo), and 3 beta,5 alpha-THAldo. Tissues metabolized approximately 10% of the labeled hormone into the same compounds by 1 h. Measurable quantities of these metabolites were also synthesized by bladders exposed to Aldo for only 10 min and then incubated in buffer for an additional 50 min without Aldo. Bladders pretreated with the spironolactone, K+-canrenoate (3.5 X 10(-4) M), and stimulated with Aldo (10(-7) M) generated a peak SCC 44 +/- 6% of that observed in matched pairs stimulated with Aldo (P less than 0.001; n = 6). K+-canrenoate also markedly diminished [3H]aldosterone metabolism at both 5 and 1 h. Thus, metabolic transformation of Aldo begins prior to hormone-induced increases in Na+ transport. Both the generation of certain metabolites (e.g., 5 alpha-reductase pathway products) and the increase in Na+ transport can be selectively inhibited by K+-canrenoate.
Renal metabolism of calcitonin
Authors: Simmons R. E. , Hjelle J. T. , Mahoney C. , Deftos L. J. , Lisker W. , Kato P. , Rabkin R.
Published: December 2017

The kidneys account for approximately two-thirds of the metabolism of calcitonin, but relatively little is known regarding the details thereof. To further characterize this process, we examined the renal handling and metabolism of human calcitonin (hCT) by the isolated perfused rat kidney. We also studied the degradation of radiolabeled salmon calcitonin (sCT) by subcellular fractions prepared from isolated rabbit proximal tubules. The total renal (organ) clearance of immunoreactive hCT by the isolated kidney was 1.96 +/- 0.18 ml/min. This was independent of the perfusate total calcium concentration from 5.5 to 10.2 mg/dl. Total renal clearance exceeded the glomerular filtration rate (GFR, 0.68 +/- 0.05 ml/min), indicating filtration-independent removal. Urinary calcitonin clearance as a fraction of GFR averaged 2.6%. Gel filtration chromatography of medium from isolated kidneys perfused with 125I-labeled sCT showed the principal degradation products to be low molecular weight forms eluting with monoiodotyrosine. Intermediate size products were not detected. In the subcellular fractionation experiments, when carried out at pH 5.0, calcitonin hydrolysis exclusively followed the activities of the lysosomal enzyme N-acetyl-beta-glucosaminidase. Typically, at pH 7.5, 42% of total degradation occurred in the region of the brush-border enzyme alanyl aminopeptidase and 29% occurred in the region of the cytosolic enzyme phosphoglucomutase. Although 9% of the calcitonin-degrading activity was associated with basolateral membrane fractions, most of this activity could be accounted for by the presence of brush-border membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
Electrode sandwich technique: a method for studying K+ transport in renal cells
Authors: Westphale H. J. , Oberleithner H.
Published: December 2017

Distal tubules were harvested from frog kidney and placed on the membrane of a K+-selective macroelectrode. Then the renal tissue was covered with a dialysis membrane to produce a closed extracellular compartment with a constant volume (40 microliter). K+ fluxes in and out of the cells could be determined, since the steady-state K+ activity during constant perfusion changed to a new steady state when perfusion was stopped. Inhibition of passive K+ permeability by the addition of Ba2+ resulted in K+ uptake by the cells because of the function of the Na+-K+ pump. Inhibition of the pump by the addition of ouabain led to K+ efflux from cells reflecting the passive K+ permeability. Because K+ net movement under control conditions (no Ba2+ or ouabain) results from both uptake and efflux, subtraction of K+ uptake (in the presence of Ba2+) from control K+ net flux reveals the passive K+ efflux. This value agrees well with that obtained with ouabain. Furosemide led to a significant K+ shift from the extracellular compartment into the intracellular compartment. Reduction of extracellular pH from 7.8 to 6.0 decreased the rate of K+ uptake by 39 +/- 7% and the K+ leak by 51 +/- 11%. We conclude that K+ uptake and K+ release can be functionally separated. This so-called “electrode sandwich technique” permits evaluation of pump and leak independently in the same cell population.
Transport of L-proline by luminal membrane vesicles from pars recta of rabbit proximal tubule
Authors: Roigaard-Petersen H. , Jacobsen C. , Sheikh M. I.
Published: December 2017

The mechanism of renal transport of L-proline by luminal membrane vesicles prepared from proximal straight tubules (pars recta) of rabbit kidney was investigated. The following picture emerges from transport studies: an electrogenic and Na+-requiring system confined to this region of nephron exists for transport of L-proline with a high affinity (Km = 0.16 mM) and low capacity (Vmax = 3.5 nmol.mg protein-1.15 S-1). Lowering the pH from 7.5 to 5.5 increased the affinity (Km lowered from 0.16 mM at pH 7.5 to 0.08 mM at pH 5.5) without changing the maximal capacity of this system. Modification of histidyl residues of the intact luminal membrane vesicles by diethyl-pyrocarbonate (DEP) completely abolished the transient renal accumulation of L-proline. Simultaneous presence of Na+ and L-proline (10 mM) protects against DEP inactivation of renal transport of radioactive L-proline. We propose that a histidyl residue may be at or close to the active site of L-proline transporter in vesicles from the pars recta.
Effect of luminal chloride on cell pH in rabbit proximal tubule
Authors: Baum M.
Published: December 2017

The present in vitro microperfusion study examined whether apical membrane chloride transport is mediated by chloride-base exchange in the rabbit proximal convoluted (PCT) and proximal straight tubule (PST) by examining the effect of the addition of luminal chloride on intracellular pH. Intracellular pH was measured fluorometrically using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. In PCT initially perfused without chloride, changing the luminal perfusate to a high chloride (148 mM)-low bicarbonate (5 mM) solution simulating late proximal tubular fluid produced a cell acidification (7.56 +/- 0.06 to 7.52 +/- 0.06, P less than 0.02) when 1 mM formate was present in the perfusate and bathing solution. This acidification was inhibited by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. This chloride-base exchange was not observed in the absence of formate, and neither acetate nor lactate produced the cell acidification observed with formate. Because the Na+-H+ antiporter could blunt a pH change, 2 mM amiloride was added to the luminal perfusate. While addition of luminal chloride produced a small cell acidification in the absence of formate (7.63 +/- 0.06 to 7.60 +/- 0.05, P less than 0.05), a much greater cell acidification was observed in the presence of 1 mM formate (7.69 +/- 0.05 to 7.58 +/- 0.06, P less than 0.01). Chloride-base exchange was only detected in the presence of formate in the PST. These studies demonstrate apical membrane chloride-base exchange in the presence of formate in the rabbit proximal tubule consistent with chloride-formate exchange.
Disparity between renal venous norepinephrine and renin responses to sodium depletion
Authors: Carroll R. G. , Lohmeier T. E. , Brown A. J.
Published: December 2017

To evaluate the hypothesis that sodium depletion produces a chronic increase in renal nerve activity, arterial and renal venous plasma norepinephrine (NE) concentrations were measured in conscious dogs subjected to various degrees of sodium depletion. After 9 days of sodium depletion (LS), there was a net loss of 69 +/- 10 meq sodium, and mean arterial pressure (MAP) was reduced from 94 +/- 5 to 88 +/- 4 mmHg. At this time plasma renin activity (PRA) was increased from a control level (sodium intake = 45 meq/day) of 0.34 +/- 0.08 to 1.47 +/- 0.26 ng angiotensin I (ANG I).ml-1.h-1 in association with an approximately sixfold increase in the PRA gradient across the kidneys. Subsequently, when captopril was infused during an additional 7 days of sodium deprivation [(LS + converting enzyme inhibitor CEI)], there was further sodium depletion (31 +/- 11 meq) and hypotension (MAP = 65 +/- 6 mmHg) and PRA and the renal PRA gradient increased even further. In marked contrast, there were no significant changes in either arterial plasma NE concentration (control = 102 +/- 5 pg/ml) or the renal arteriovenous gradient of plasma NE concentration during either LS or LS + CEI. These experiments show a distinct disparity between changes in the PRA and the plasma NE concentration gradient across the kidneys during LS and fail to support the contention that increased renal nerve activity is an important long-term adaptive response to sodium depletion.
Renal memory after potassium adaptation: role of Na+-K+-ATPase
Authors: Mujais S. K.
Published: December 2017

The present study was designed to explore the time course of the resolution of enhanced Na+-K+-ATPase activity in the cortical collecting tubule (CCT) and the parallel changes in renal K excretion that are characteristic of potassium adaptation. Potassium-adapted male Sprague-Dawley rats manifested an enhanced kaliuretic response to an acute intravenous load of KCl and a doubling of Na+-K+-ATPase activity in the CCT. Withdrawal of dietary K loading from these adapted rats was associated with a gradual resolution of these adaptive biochemical (t1/2 of Na+-K+-ATPase return to base line 48 h) and excretory changes. During this resolution phase, however, a temporal discrepancy was uncovered between the change in dietary K and the slower changes in enzyme activity and renal K excretion with a persistence of the enhanced kaliuresis leading to a negative K balance. We conclude that the slow inactivation, after withdrawal of K loading, of the increased membrane transport proteins of K adaptation, will manifest as a renal memory of the antecedent excretory requirements.
Complexing activity and excretion of 2,3-dimercapto-1-propane sulfonate in rat kidney
Authors: Klotzbach J. M. , Diamond G. L.
Published: December 2017

The renal handling of the heavy metal complexing agent, 2,3-dimercapto-1-propane sulfonate (DMPS), was examined in the isolated perfused rat kidney (IPRK). Net tubular secretion of DMPS was saturable and blocked by p-aminohippuric acid (PAH) and probenecid (PRB), indicating involvement of carrier-mediated transport in the excretion of DMPS. DMPS was oxidized to a disulfide form (DMPSS) in perfusate and reduced to a sulfhydryl form (DMPSH) in kidney. In kidneys isolated from rats pretreated with HgCl2, DMPS produced a dose-dependent decrease in retention of inorganic mercury, an increase in urinary excretion of mercury, and an increase in the amount of mercury transferred from kidney into venous perfusate. At a maximally effective dose, 40% of the renal mercury content was excreted in urine during 30 min of perfusion. Urinary excretion of mercury induced by DMPS was completely blocked by concentrations of PRB that blocked tubular secretion of DMPS and decreased uptake of DMPS in kidney. Thus tubular secretion of DMPS and reduction of DMPSS to DMPSH are important in the renal handling of DMPS and may contribute to the activity of DMPS as a complexing agent for renal mercury.
Interleukin 1 modulation of renal epithelial glucose and amino acid transport
Authors: Kohan D. E. , Schreiner G. F.
Published: December 2017

We have investigated the effect of immune factors on glucose and amino acid transport by proximal tubular epithelium. Proximal tubular cells were obtained by enzymatic digestion of mouse renal cortex and grown to confluent monolayers. alpha-[14C]methylglucoside (AMG), D-[3H]-aspartate, L-[3H]leucine, and L-[3H]arginine uptake were assayed. Proximal tubular epithelium coincubated with supernatants derived from lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages had a twofold increase in AMG and aspartate uptake that was sodium dependent, was prevented by cycloheximide or actinomycin D, and was not associated with changes in cell growth or differentiation. Chromatographic separation of the macrophage supernatant yielded one fraction, mol wt 16,000-20,000, that enhanced AMG and aspartate uptake and contained interleukin 1 (IL 1) determined by bioassay. Recombinant IL 1 (mol wt 17,500) reproduced changes in AMG and aspartate uptake seen with macrophage supernatants. In contrast, neither macrophage supernatants nor IL 1 affected sodium-independent leucine or arginine transport. IL 1 directly increased 22Na transport into proximal tubular cells. These data indicate that macrophages, via IL 1 secretion, are capable of modulation of sodium-linked solute transport in proximal tubular epithelium.
Immunodissection of mitochondria-rich cells from rabbit outer medullary collecting tubule
Authors: Burnatowska-Hledin M. A. , Spielman W. S.
Published: December 2017

Two types of mitochondria-rich (MR) cells have been identified in the rabbit collecting tubule based on differences in immuno- and lectin cytochemistry. We have produced a monoclonal antibody, immunoglobulin (Ig) G1 (mr-mct), that reacts specifically with the MR cells (identified by positive histochemical staining for succinate dehydrogenase) found predominantly in the outer medulla (OM) and cells of the proximal tubule. IgG1 (mr-mct) reacted with 18 +/- 2% of the cells of the outer medullary collecting tubule (OMCT) and did not colocalize with peanut lectin-binding MR cells in the cortex. To isolate MR-OMCT cells, collecting tubule cells from collagenase dispersions of the OM were first adsorbed onto plates treated with a monoclonal antibody reactive against all of the OMCT cells. Of the isolated OMCT cells, 17% reacted with IgG1 (mr-mct). Cells were then detached from the plate and transferred to plates coated with IgG1. Greater than 70% of the adsorbed cells were MR as determined by positive staining with IgG1 (mr-mct). This enrichment of MR-OMCT cells was associated with a severalfold increase in adenosine 3',5' cyclic monophosphate (cAMP) production in response to isoproterenol and an attenuated increase in cAMP production to vasopressin. In summary, we report the isolation of highly enriched populations of MR cells from the OM using two-stage solid-phase immunoadsorption. This approach should provide a useful and convenient method for further investigations of the physiological role of these poorly understood tubular cells.