bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional differentiation of cell types of cortical collecting duct
Authors: O'Neil R. G. , Hayhurst R. A.
Published: December 2017

Interference-contrast and fluorescent microscopy were used to differentiate between the two cell types--principal cells (PC) and intercalated cells (IC)--of the isolated perfused cortical collecting duct of the rabbit. Using Hoffman Modulation Contrast optics, two types of cell outlines could be identified: "hexagonal" and "circular" profiles. To characterize the cell types further, the binding of fluorescein-labeled peanut lectin, which has been shown to be specific for the luminal cell membrane of the IC, was monitored with epifluorescent techniques. The lectin was observed to bind to the circular cell type only, confirming it as the IC. With use of the fluorescent nuclear probe acridine orange to quantitate the total number of cells per millimeter of tubule length, the fraction of ICs (lectin-binding cells) was estimated to average 29%, and the fraction of PCs (non-lectin-binding cells) to average 71% of all cells. The studies were extended to functionally separate between the two cell types by monitoring cell swelling when a lumen-to-bath current pulse was passed. Current-induced swelling was observed only in the PC and could be inhibited by the luminal addition of both the Na+ channel blocker amiloride, and the K+ channel blocker barium, thereby implicating the PC in the process of Na+ absorption and K+ secretion in this tissue. It is concluded that optical techniques can be applied to the cortical collecting duct perfused in vitro to differentiate between and study functional properties of the cell types.
Effect of parathyroid hormone on the determinants of glomerular filtration in dogs
Authors: Marchand G. R.
Published: December 2017

Elevated levels of parathyroid hormone (PTH) often are associated with reduced glomerular filtration rate (GFR) in humans. Although PTH has been reported to reduce the ultrafiltration coefficient (Kf) in rats, GFR declined only if they were plasma expanded. In contrast, PTH does not reduce GFR in dogs, despite filtration pressure disequilibrium. To evaluate this apparent discrepancy, the determinants of GFR were measured in acutely thyroparathyroidectomized dogs. In the absence (n = 8) and presence (n = 10) of synthetic bovine PTH, GFR was 29 +/- 3 and 26 +/- 2 ml/min; Single nephron glomerular filtration rate was 58 +/- 4 and 51 +/- 3 nl/min; glomerular plasma flow was 248 +/- 22 and 250 +/- 24 nl/min; glomerular capillary pressure was 58 +/- 2 and 61 +/- 3 mmHg; Bowman's space pressure was 19 +/- 2 and 19 +/- 1 mmHg; and systemic oncotic pressure was 19 +/- 0.8 and 18 +/- 0.5 mmHg. Average effective filtration pressure (EFP) was significantly greater in the presence (18.6 +/- 1.3 mmHg) than in the absence (14.6 +/- 0.9 mmHg) of PTH. Therefore, Kf per glomerulus calculated from these data was significantly (P less than 0.01) less in the presence than in the absence of PTH (2.91 +/- 0.29 and 3.98 +/- 0.16 nl X min-1 X mmHg-1, respectively). It is concluded that PTH reduced Kf. Whereas this effect predicts reduced GFR in dogs, given filtration pressure disequilibrium, a concomitant increase in EFP maintained GFR in the present study.
Renal handling and production of plasma and urinary adenosine
Authors: Thompson C. I. , Sparks H. V. , Spielman W. S.
Published: December 2017

The present study was undertaken to determine the renal handling of plasma adenosine and the relative contribution of the kidney to the adenosine in the renal venous plasma and urine. Injections of radiolabeled adenosine, as a tracer of arterial adenosine, along with reference compounds (either inulin or 9-beta-D-arabinofuranosyl hypoxanthine, an analogue of adenosine that does not occupy the nucleoside carrier) were coupled with measurements of endogenous adenosine in the arterial and renal venous plasma and urine of 11 anesthetized dogs. The arterial and venous concentration of endogenous adenosine was 60 +/- 16 and 52 +/- 10 nM, respectively. Urinary adenosine concentration was 312 +/- 53 nM and the fractional excretion was 0.71 +/- 0.14. Of the radiolabeled adenosine injected into the renal artery, approximately 53 +/- 3% of the filtered tracer was recovered in the urine, and only 11 +/- 1% of the tracer was recovered in the venous plasma. These results demonstrate uptake of adenosine from both the tubular and vascular compartments, and analysis of single-injection multiple-indicator curves indicates that a substantial amount of the extracted arterial adenosine enters and remains in cells. We conclude that arterial plasma contributes significantly to adenosine excreted in the urine but only minimally to renal venous adenosine. Furthermore, any intervention that alters cellular uptake and metabolism of adenosine may lead to significant changes in extracellular adenosine.
Tubular transport responses to angiotensin
Authors: Harris P. J. , Navar L. G.
Published: December 2017

Angiotensin II (ANG II) is a powerful effector agent in the regulation of extracellular volume and exerts an important influence on renal sodium excretion. In addition to its effects on aldosterone secretion, ANG II acts directly on the kidney causing retention of sodium at low (physiological) doses and enhanced sodium excretion at high doses. The mechanism for these responses involves vasoconstrictor actions of ANG II on the renal vasculature and a direct action of the peptide on tubular reabsorption. Micropuncture and microperfusion studies have demonstrated that proximal tubular sodium and water transport are stimulated by physiological concentrations (10(-12) to 10(-10) M) of ANG II on the peritubular side, whereas higher doses (10(-7) M) cause inhibition. A luminal site of action in the proximal tubule has also been reported and additional more distal sites are indicated. [125I]ANG II binding sites on the brush border and basolateral membranes of proximal tubule cells have high affinity (Kd in the nanomolar range) for ANG II and lower affinity for ANG III. The biphasic action of ANG II is exerted directly on the epithelial cells and appears to be electroneutral. The data indicate that ANG II binds to receptors on the basolateral cell membrane and alters the rate of entry of sodium through the luminal membrane to increase or decrease, depending on the concentration of peptide. Several possible cellular mechanisms that could mediate these responses are discussed.
Water and urea transport in renal microvillus membrane vesicles
Authors: Verkman A. S. , Dix J. A. , Seifter J. L.
Published: December 2017

Light scattering was used to measure the water and urea permeability of brush border membrane vesicles (BBMV) isolated from rabbit renal cortex. In stop-flow experiments, exposure of BBMV to a 200 mM inwardly directed mannitol gradient gave a monophasic time course of decreasing BBMV volume corresponding to an osmotic water permeability (Pf) of 1.1 +/- 0.1 X 10(-2) cm/s at 37 degrees C. The temperature dependence of Pf was biphasic with delta H = 2 kcal/mol for T less than 33 degrees C and delta H = 14 kcal/mol for T greater than 33 degrees C. A 200 mM inwardly directed urea gradient gave a biphasic time course of BBMV volume due to rapid water efflux (approximately 50 ms) followed by slower urea influx (1-5 s) with urea permeability (Purea) of 2.4 +/- 0.2 X 10(-6) cm/s. Preincubation of BBMV with increasing [urea] reversibly inhibited both urea flux (Kd = 1,200 mM) and thiourea flux (Kd = 370 mM) according to a single-site inhibition model, suggesting a saturable urea carrier. Comparison of BBMV Pf and Purea with proximal tubule transepithelial water and urea transport rates suggests that the permeability of the tubular apical membrane (BBMV) is high enough to support a transcellular route for both osmotic water and urea transport.
Arginine vasotocin and glomerular filtration rate in saltwater-acclimated ducks
Authors: Gerstberger R. , Kaul R. , Gray D. A. , Simon E.
Published: December 2017

We examined the relationship between whole kidney glomerular filtration rate (GRF) and the plasma concentration of immunoreactive arginine vasotocin (AVT), the avian antidiuretic hormone, in saltwater-acclimated ducks. During steady-state diuresis, driven by infusion of sodium chloride solutions, transient reductions of [14C]inulin clearance (3 ml X min-1 X kg-1) occurred when plasma AVT concentrations were roughly doubled by systemic injection of synthetic AVT or after stimulation of endogenous AVT release by perfusion of the third ventricle with hypertonic artificial cerebrospinal fluid (CSF). Transient increases in GFR occurred when plasma AVT was reduced during inhibition of its endogenous release by hypotonic ventricle perfusion. GFR also increased after injection of AVT antiserum but returned to control values within 30 min, while plasma AVT concentration remained very low for at least 1 day. During antidiuresis evoked by infusion of strongly hypertonic saline, GFR values estimated from plasma disappearance curves of [125I]iothalamate were not different from the GFR values estimated subsequently with the same method in the same ducks made diuretic by hypotonic saline infusions, although AVT concentrations were depressed during the latter as compared with the former infusion. Factors other than AVT must be important for the control of GFR during sustained osmotic stress.
Effect of pH on phosphate transport in rat renal brush border membrane vesicles
Authors: Amstutz M. , Mohrmann M. , Gmaj P. , Murer H.
Published: December 2017

The initial linear rate of phosphate uptake was analyzed in rat renal brush border membrane vesicles. An increase in medium pH from 6.0 to 8.0 increased the sodium gradient-dependent phosphate uptake about 20-fold. Sodium-independent phosphate uptake was not altered in this pH range. At pH 7.4 an intravesicular acid pH stimulated the initial linear uptake rate (20-25%). The apparent Km for sodium increased from about 100 to 200 mM when pH was decreased from 7.4 to 6.4. The Hill coefficient for sodium interaction was close to 2 and was unaffected by pH. Increasing external sodium reduced the apparent Km of the transport system for phosphate independent of pH. Variations of phosphate concentration had no influence on the apparent Km for sodium. At high sodium concentrations, small effects (20-30%) of pH on the apparent Vmax of the transport system were found; measured at saturating sodium concentrations, the apparent Km values calculated on the basis of total phosphate were increased (50-60%) when pH was decreased from 7.4 to 6.4. The data indicate that the major effect of pH is to modify the interaction of the transport system with sodium. At nonsaturating sodium concentrations, this resulted indirectly in a reduction in the affinity for phosphate related to a different occupancy of the sodium binding site. The differences of transport rate at low phosphate and high sodium concentrations could be explained by preferential transport of divalent phosphate as well as by pH effects on other carrier properties.
Effects and interrelationships of PTH, Ca2+, vitamin D, and Pi in acid-base homeostasis
Authors: Hulter H. N.
Published: December 2017

Chronic administration of 1,25(OH)2D or PTH increases the set point at which plasma bicarbonate concentration is regulated by the kidney and thereby maintains metabolic alkalosis in a variety of species. The renal mechanism(s) responsible for the chronic acid excretory response to 1,25(OH)2D and PTH administration have not been defined, but indirect evidence suggests effects on distal nephron segments. With either hormone in dogs, but not in rats, metabolic alkalosis is generated in part by extrarenal mechanisms. Contrary to the variable finding of hyperchloremic acidosis in human primary hyperparathyroidism, a steady state of mild metabolic alkalosis of renal origin is achieved in normal human subjects infused chronically with PTH. The multiple potential mechanisms responsible for this discrepancy will require careful consideration in future investigations. The acute and chronic effects of plasma calcium concentration on both renal and extrarenal acid-base homeostasis are incompletely understood and require extensive further investigation. Studies in rats have suggested that phosphate depletion results in important counterbalancing renal acidosis and extrarenal alkalosis-producing effects. Chronic hypophosphaturia in the absence of appreciable hypophosphatemia can also result in impaired renal acidification by virtue of phosphate's property as a luminal buffer.
Peritubular protein modulates neutral active NaCl absorption in rabbit proximal convoluted tubule
Authors: Baum M. , Berry C. A.
Published: December 2017

To assess directly the effect of increasing and decreasing peritubular protein concentration on active NaCl absorption, rabbit proximal convoluted tubules were perfused with a high-chloride solution simulating late proximal tubular fluid and bathed in a similar solution containing 0, 6, or 10 g/dl albumin. A direct examination of the active component of NaCl absorption was ensured by 1) the reduction of luminal solutes other than NaCl (no glucose or alanine and only 5 mM HCO-3), and 2) the use of perfusate and bathing solutions in approximate Donnan equilibrium, so that electrochemical driving forces responsible for passive net NaCl absorption are eliminated. When bathing solution albumin concentration was reduced from 6 to 0 g/dl, volume absorption (Jv) was reduced significantly from 0.39 +/- 0.07 to 0.22 +/- 0.08 nl X mm-1 X min-1. When bathing solution albumin concentration was increased from 6 to 10 g/dl, Jv increased significantly from 0.26 +/- 0.04 to 0.37 +/- 0.04 nl X mm-1 X min-1. When proximal convoluted tubules were bathed in 0, 6, or 10 g/dl albumin at 20 degrees C, Jv was not different from zero in all periods, confirming that changes in bathing solution albumin require the presence of active transport to influence NaCl absorption. The transepithelial potential difference attributable to active transport was not different from zero in all periods of all protocols, demonstrating that active NaCl absorption was electroneutral. In conclusion, these data show directly that peritubular protein concentration modulates neutral active NaCl absorption in the rabbit proximal convoluted tubule.
Rat renal hemodynamics during venous compression: roles of nerves and prostaglandins
Authors: Corradi A. , Arendshorst W. J.
Published: December 2017

Experiments were conducted on euvolemic rats to characterize renal hemodynamic responses to a unilateral increase in renal venous pressure. Ipsilateral renal blood flow (RBF, electromagnetic flow probe) was measured in four groups to determine the roles of the renal nerves and endogenous prostaglandins. In control rats, elevation of venous pressure (3 to 22 mmHg) produced vasoconstriction and a 16% increase in renal vascular resistance (RVR) at 130 mmHg arterial pressure (P less than 0.001). In acutely denervated kidneys, a 19-mmHg increase in venous pressure reduced RBF but did not alter RVR (5% decrease), since there were proportional decreases in RBF and the arteriovenous pressure gradient. Indomethacin-treated rats with innervated kidneys responded to a similar increase in venous pressure with pronounced constriction; RVR increased by 50% (P less than 0.005). Venous compression elicited a 24% increase in RVR (P less than 0.05) in indomethacin-treated rats with denervated kidneys. The opposing effects of denervation and indomethacin treatment were significant and noninteractive. The findings indicate 1) activation of an ipsilateral renorenal neural reflex mediated a significant portion of the vasoconstriction; and 2) enhanced synthesis of prostaglandins produced net dilatory effects that attenuated the neurally mediated constriction. The opposing actions of the renal nerves and prostaglandins on the RVR responses to increased venous pressure were directly related to arterial pressure between 70 and 130 mmHg. In response to decrements in arterial pressure, the general pattern of vasodilation was not impaired by denervation of indomethacin when venous pressure was normal or elevated. These observations indicate that the origin of the pressure change, i.e., arterial vs. venous, engages different vasoactive factors that are responsible for varying circulatory responses in the rat kidney.
Mineralocorticoid regulation of apical cell membrane Na+ and K+ transport of the cortical collecting duct
Authors: Sansom S. C. , O'Neil R. G.
Published: December 2017

The effects of mineralocorticoid (DOCA) treatment of rabbits on the Na+ and K+ transport properties of the cortical collecting duct apical cell membrane were assessed using microelectrode techniques. Applying standard cable techniques and equivalent circuit analysis to the isolated perfused tubule, the apical cell membrane K+ and Na+ currents and conductances could be estimated from the selective effects of the K+ channel blocker Ba2+ and the Na+ channel blocker amiloride on the apical membrane; amiloride treatment was observed also to decrease the tight junction conductance by an average of 10%. After 1 day of DOCA treatment, the Na+ conductance and current (Na+ influx) of the apical cell membrane doubled and remained elevated with prolonged treatment for up to 2 wk. The apical cell membrane K+ conductance was not influenced after 1 day, although the K+ current (K+ secretion) increased significantly due to an increased driving force for K+ exit. After 4 days or more of DOCA treatment the K+ conductance doubled, resulting in a further modest stimulation in K+ secretion. After 2 wk of DOCA treatment the tight junction conductance decreased by near 30%, resulting in an additional hyperpolarization of the transepithelial voltage, thereby favoring K+ secretion. It is concluded that the acute effect (within 1 day) of mineralocorticoids on Na+ and K+ transport is an increase in the apical membrane Na+ conductance followed by delayed chronic alterations in the apical membrane K+ conductance and tight junction conductance, thereby resulting in a sustained increased capacity of the tubule to reabsorb Na+ and secrete K+.
Calcium transport and inner mitochondrial membrane damage in renal cortical mitochondria
Authors: Weinberg J. M. , Humes H. D.
Published: December 2017

Ca2+ uptake and efflux processes, as they are manifested during procedures used for isolation of renal cortical mitochondria, were characterized in order to provide a better basis for making inferences from isolated mitochondria about the in vivo state of mitochondrial Ca2+ homeostasis in both normal and injured tissues and to better define the mechanisms by which Ca2+ mediates injury to renal cortical mitochondria. Mitochondrial Ca2+ uptake predictably occurred when the capacity of the Ca2+ chelator added to the isolating medium to maintain free Ca2+ in the submicromolar range was exhausted unless ruthenium red was present to specifically inhibit the Ca2+ uniport. Ca2+ uptake during isolation ultimately led to loss of accumulated Ca2+ and intramitochondrial K+ as well as to deterioration of respiratory function. Extramitochondrial Ca2+ also evoked the latter two events in the absence of Ca2+ uptake but only at much higher medium Ca2+ levels than were required when Ca2+ uptake was allowed to occur. Studies using mitochondria loaded with known amounts of Ca2+ at 4 degrees C and then subjected to a reisolation procedure including all the steps of normal isolation demonstrated that phosphate markedly potentiated Ca2+-induced alterations of mitochondrial membrane permeability properties. Of several agents studied singly, fatty acid-free albumin was most effective in blocking Ca2+ + phosphate-induced alterations of mitochondrial membrane permeability. The protective effect of fatty acid-free albumin was further enhanced by combining it with Mg2+, dibucaine, or oligomycin + ADP. This study thus quantitatively defined conditions under which Ca2+ uptake can be expected to occur during mitochondrial isolation, demonstrated that the effects of this Ca2+ uptake on mitochondrial properties are similar to those previously elucidated in mitochondria studied at warmer temperatures, and defined methods suitable for blocking such Ca2+ movements and their deleterious effects.
NMR measurements of intracellular sodium in the rabbit proximal tubule
Authors: Gullans S. R. , Avison M. J. , Ogino T. , Giebisch G. , Shulman R. G.
Published: December 2017

The present study evaluated the use of nuclear magnetic resonance (NMR) spectroscopy to monitor directly and continuously intracellular sodium levels in rabbit renal cortical tubule suspensions. When the paramagnetic shift reagent dysprosium tripolyphosphate was added to the extracellular medium it was possible to resolve signals from intracellular and extracellular sodium without adversely affecting cellular viability. An efflux of intracellular sodium against a significant concentration gradient was observed when sodium-loaded cells were warmed from 4 to 37 degrees C. At 37 degrees C in steady state, inhibition of Na+-K+-ATPase activity by ouabain increased intracellular sodium content in a dose-dependent and time-dependent manner. A biphasic time course of increased intracellular sodium following ouabain (10(-3) M) suggested that the sodium permeability of the plasma membrane may decrease following pump inhibition, thus limiting sodium influx. Nystatin, an agent known to facilitate sodium entry across cell membranes, increased intracellular sodium fivefold. In another series of experiments several maneuvers were performed to ascertain the fraction of intracellular sodium that was NMR visible. Quantitative assessment of either an efflux or influx of sodium indicated that the NMR visibility of the transported sodium was 100%. Furthermore, disruption of the cell membranes with Triton X-100 showed that the entire pool of intracellular sodium was 100% NMR visible.(ABSTRACT TRUNCATED AT 250 WORDS)
Electrogenicity of the Na-K-ATPase pump in bullfrog cornea epithelium
Authors: Carrasquer G. , Ahn S. , Schwartz M. , Rehm W. S.
Published: December 2017

The effect of changing the K concentration in the aqueous solution was studied in the frog cornea. In general, when the K concentration was increased from 4 to 20 or 79 mM, the transepithelial PD and resistance decreased. If K was decreased from 79 to 4, 20 to 4, or 4 to 0 mM, or any other combination, the PD and resistance increased. These are normal PD responses. If after a K-free period of more than 5-10 min the K was increased to 4 mM, the PD increased, an anomalous PD response. If K was increased from 0 to 20 mM, there was an initial PD increase (anomalous response) followed by a PD decrease (normal response). If K was increased from 0 to 79 mM the PD decreased, normal response only. The resistance decreased with every increase in K concentration. Anomalous responses were abolished in Na-free solutions and in the presence of both 10(-3) M ouabain and 10(-4) M vanadate in the aqueous solution. We interpret the results on the basis of two pathways, a simple K-conductive pathway and an electrogenic Na-K-ATPase pump pathway with more Na's than K's per cycle. The normal or anomalous PD responses to changes in aqueous K concentration depend on the relative resistance of the two pathways.
Deoxycorticosterone-stimulated bicarbonate secretion in rabbit cortical collecting ducts: effects of luminal chloride removal and in vivo acid loading
Authors: Garcia-Austt J. , Good D. W. , Burg M. B. , Knepper M. A.
Published: December 2017

To assess the role of cortical collecting duct bicarbonate secretion in the regulation of net acid excretion, we have sought to identify what factors influence the secretion rate. Net and unidirectional bicarbonate fluxes were measured in isolated perfused cortical collecting ducts from deoxycorticosterone-treated rabbits. The collecting ducts secreted bicarbonate at 11-24 pmol X mm-1 X min-1, confirming the high rate seen in earlier studies. Oral acid loading (50 mM NH4Cl drinking water) completely inhibited the net bicarbonate secretion. The bath-to-lumen flux was markedly reduced with acid loading, but the lumen-to-bath flux changed very little. In tubules from rabbits treated with deoxycorticosterone (but not NH4Cl), luminal chloride replacement with either sulfate or gluconate completely and reversibly inhibited the net bicarbonate secretion. The bath-to-lumen flux was greatly inhibited, but there was little change in the lumen-to-bath flux. We conclude: 1) High rates of bicarbonate secretion can be induced in rabbit cortical collecting ducts by chronic treatment of the animals with deoxycorticosterone. 2) When deoxycorticosterone-treated rabbits were made acidotic by oral administration of NH4Cl, the bicarbonate secretion was prevented, indicating that the systemic acid-base state of the animal may be an important factor regulating bicarbonate secretion. 3) Replacement of chloride in the lumen with sulfate inhibits bicarbonate secretion in the cortical collecting duct, an effect which may explain in part the decrease in urinary pH in response to sulfate infusions in mineralocorticoid-stimulated animals.
Role of myosin light-chain phosphorylation and microtubules in stress fiber morphology in cultured mesangial cells
Authors: Kreisberg J. I. , Venkatachalam M. A. , Radnik R. A. , Patel P. Y.
Published: December 2017

Induced elevations in intracellular cAMP caused remarkable shape changes in cultured mesangial cells that were prevented by prostaglandin E2 (PGE2). The purpose of this study was to determine the morphological and physiological basis for these alterations. Coincident with elevated levels of cAMP and shape change there was rapid dissolution of stress fibers. Cytochalasin B treatment also caused shape change and stress fiber dissolution. Stress fibers were visualized by fluorescence microscopy after appropriate staining. In such cells, microtubules were intact. PGE2 prevented stress fiber loss as well as shape change if it was included in the medium from the outset, or restored stress fibers and normal morphology within 30 min if it was added following shape change. Agents that depolymerize microtubules also prevented both stress fiber loss and shape change. Coincident with stress fiber loss and shape change induced by elevations of cAMP, there was a decrease in the rate of [32P]-orthophosphate incorporation into myosin light chain; this was also prevented or reversed by PGE2. Remarkably, PGE2 alone caused an increase in the rate of [32P]orthophosphate incorporation into myosin light chain in cells that were otherwise untreated. Phosphorylation of the light chain of myosin may be an important factor in the maintenance of stress fiber morphology. The results of this study point out complex interrelationships between microtubules, and stress fibers in the maintenance of cell shape needing further study. The model systems that are presented seem suited for such investigation.
Intracellular recordings from renin-positive cells of the afferent glomerular arteriole
Authors: Buhrle C. P. , Nobiling R. , Taugner R.
Published: December 2017

Intracellular recordings were made in juxtaglomerular granulated (JG) cells and in vascular smooth muscle (VSM) cells in afferent arterioles of hydronephrotic mouse kidneys. Both cell types did not differ in their passive and active electrical membrane properties; membrane potential was about -58 mV, input resistance exceeded 400 M omega, and JG as well as VSM cells showed spontaneous depolarizations resembling excitatory junction potentials and active responses observed in smooth muscle cells of other blood vessels in various species. These depolarizations, attributed to spontaneous transmitter release from adrenergic terminals, were extremely polymorphous and quite frequent. Epinephrine, norepinephrine, phenylephrine, arginine vasopressin, and angiotensin II depolarized JG and VSM cells, but isoproterenol and orciprenaline had no effect. A hyperpolarizing action of catecholamines was never observed. It is suggested that, in this in vitro preparation, isoproterenol increases renin secretion by a mechanism independent of membrane potential changes. Depolarizations mediated by alpha-mimetic agents, arginine vasopressin, and angiotensin II, as well as by the junctional activity may inhibit renin secretion by an increased calcium influx into JG cells.
Effects of dDAVP on rat juxtamedullary nephrons: stimulation of medullary K recycling
Authors: Elalouf J. M. , Roinel N. , de Rouffignac C.
Published: December 2017

The effects of 1-desamino-8-D-arginine vasopressin (dDAVP) on the handling of water and electrolytes by the juxtamedullary nephrons were studied on rats with reduced circulating levels of antidiuretic hormone (ADH), parathyroid hormone, calcitonin, and glucagon, all of which stimulate the adenylate cyclase system of the thick ascending limb and the distal tubule. In such hormone-deprived rats and in hormone-deprived + dDAVP rats, the concentration of Na, Cl, and total solutes was lower in the ascending than in the descending limbs, whereas the inulin concentration was similar at both sites. dDAVP did not alter the fraction of NaCl remaining in the thin limbs, but tended to reduce that of Mg and Ca. On the other hand, dDAVP significantly increased the fraction of filtered K remaining from 65.8 +/- 5.2 to 107.3 +/- 15.8%. A direct correlation was observed between the fraction of filtered K remaining at the tip of the juxtamedullary loops and the fractional excretion rate of K in urine. Since dDAVP enhances distal K net secretion, as previously shown in our laboratory, these results indicate that the medullary recycling of K from nephron terminal segments to Henle's loop of juxtamedullary nephrons is stimulated by this peptide.
Centrally administered naloxone blocks reflex natriuresis after acute unilateral nephrectomy
Authors: Lin S. Y. , Humphreys M. H.
Published: December 2017

Acute unilateral nephrectomy (AUN) leads to a natriuresis and kaliuresis by the remaining kidney through reflex mechanisms involving opiate receptors. To determine whether the opiate receptors mediating these responses are located in the central nervous system, we carried out AUN in anesthetized rats undergoing continuous ventriculocisternal perfusion (VCP) with artificial cerebrospinal fluid (CSF). AUN caused large increases in both Na (UNaV) and K (UKV) excretion without changes in glomerular filtration rate or arterial blood pressure. When the opiate receptor antagonist naloxone was added to the perfusate to achieve a perfusion rate of 32 micrograms X kg-1 X h-1, AUN failed to increase either UNaV or UKV by the remaining kidney. This dose of naloxone, however, was without effect when infused intravenously. Addition of thyrotropin-releasing hormone (TRH) to the artificial CSF to achieve a VCP rate of 50 micrograms X kg-1 X h-1 also blocked the expected increase in UNaV and UKV by the remaining kidney after AUN. Infusion of TRH intravenously at the same rate did not interfere with the postnephrectomy natriuresis or kaliuresis. Higher intravenous infusion rates of TRH (1 and 2 mg X kg-1h-1) prevented the postnephrectomy natriuresis without affecting the kaliuresis. These results indicate that the effect of naloxone to block the reflex natriuresis and kaliuresis after AUN resides largely in the central nervous system. The blockade by naloxone of the postnephrectomy natriuresis is duplicated by centrally administered TRH, providing another example of the interaction of this hormone with the endogenous opioid system. Large intravenous infusions of TRH also block the postnephrectomy natriuresis but not the kaliuresis.
Evidence for a DCCD-sensitive component of proximal bicarbonate reabsorption
Authors: Bank N. , Aynedjian H. S. , Mutz B. F.
Published: December 2017

To examine the possible contribution of active H+ secretion mediated by brush border enzymes to proximal tubule HCO-3 absorption, paired reperfusions of surface proximal convoluted tubules were performed with the inhibitor dicyclohexylcarbodiimide (DCCD). In control studies using a solution devoid of HCO-3 but containing 5.5 mM glucose, 1 mM DCCD had no effect on glucose or fluid (Na+) absorption, suggesting that this inhibitor did not interfere with sodium entry at the brush border or mitochondrial energy production (ATP synthesis). In experiments using a perfusion solution containing 18-25 mM HCO-3, DCCD caused a fall in absolute CO2 absorption of approximately 15% under eucapneic conditions and 30% during acute hypercapnia. One millimole per liter amiloride (an inhibitor of the passive Na+-H+ exchanger) caused a 15% inhibition of CO2 absorption during acute hypercapnia and a disproportionately large reduction in fluid (Na+) absorption. The latter was not due to cell poisoning, since 1 mM amiloride had no inhibitory effect on fluid or glucose absorption when a HCO-3-free perfusion solution was used. Addition of 1 mM DCCD to a perfusion solution containing either 10(-3) M amiloride or 10(-4) M acetazolamide caused a significant inhibition of CO2 absorption compared with amiloride or acetazolamide alone. The observations are consistent with the view that in addition to passive Na+-H+ exchange, active transport mediated by either a H+-ATPase or a redox-driven H+ pump in the brush border contributes significantly to HCO-3 absorption in the proximal tubule.
Effects of intraluminal pH and dietary phosphate on phosphate transport in the proximal convoluted tubule
Authors: Quamme G. A. , Mizgala C. L. , Wong N. L. , Whiting S. J.
Published: December 2017

The proximal tubule cell adjusts its phosphate absorption appropriately to meet the needs of the organism. Studies were performed to characterize some of the cellular changes involved with dietary phosphate adaptation. First, early proximal convoluted tubules were perfused with equilibrium Ringer solutions buffered to pH 7.65 or 6.5. Saturation kinetics for phosphate transport were determined at each pH value. Rats maintained on a diet of normal phosphate composition demonstrated the apparent Jmax and Km parameters about twofold greater with intraluminal pH 7.65 vs. pH 6.5. The Jmax values increased to 53.47 +/- 3.71 and 42.73 +/- 5.48 pmol X min-1 X mm-1, respectively, when the rats were placed on a phosphate-restricted diet for 5 days. By contrast, adaptation to a high dietary phosphate content resulted in diminished phosphate absorption, 8.53 +/- 1.80 and 12.87 +/- 1.61 pmol X min-1 X mm-1, for the respective pH 7.65 and 6.5 values. Second, the effect of peritubule phosphate concentration was evaluated at constant intraluminal phosphate concentrations. Unidirectional lumen-to-blood phosphate efflux was inhibited at all plasma phosphate concentrations in animals maintained on normal dietary phosphate. By contrast, rats adapted to a low phosphate diet exhibited an increase in phosphate absorption: pH 7.65, 86.21 +/- 2.63, and pH 6.5, 140.84 +/- 86.76 pmol X min-1 X mm-1 when plasma concentrations were elevated two- or three-fold from 2.4 to 6.4 mM. This was attributed to enhanced phosphate exchange on the basolateral membrane. Further hyperphosphatemic levels, above 6.4 mM, inhibited phosphate absorption. These data suggest that net phosphate absorption is determined, in part, by factors other than sodium-dependent uptake of phosphate by the brush border membrane including intracellular pH and peritubular phosphate that act in concert to control renal phosphate absorption.
Ammonium replaces potassium in supporting sodium transport by the Na-K-ATPase of renal proximal straight tubules
Authors: Garvin J. L. , Burg M. B. , Knepper M. A.
Published: December 2017

Ammonium is capable of replacing potassium to support the hydrolysis of ATP by the Na-K-ATPase in many tissues. Whether ammonium supports the transport function of the Na-K-ATPase in the kidney (where such a substitution could be physiologically important) has not been studied, however. To address this issue, we determined the rates of fluid absorption and bicarbonate absorption (measured as total carbon dioxide) in the proximal straight tubule of the rabbit where both processes are dependent on sodium transport by the Na-K-ATPase. Both fluid absorption and total carbon dioxide absorption were significantly inhibited by potassium removal from the bath and perfusate. When ammonium was included in the perfusate and bath (replacing potassium completely), both fluid absorption and bicarbonate absorption occurred at rates indistinguishable from the rates observed with potassium present (and ammonium absent). We conclude that ammonium can replace potassium in supporting sodium transport by the Na-K-ATPase of the proximal straight tubule. Interaction between ammonium and potassium on the Na-K-ATPase could be important in this and other nephron segments.
Metabolic responses of the kidney in fetal sheep: effect of acute and spontaneous hypoxemia
Authors: Iwamoto H. S. , Rudolph A. M.
Published: December 2017

To examine the effects of hypoxemia on carbohydrate and O2 consumption by the fetal kidney, we inserted catheters into the descending aorta, inferior vena cava, and left renal vein of 14 fetal sheep at 120-130 days gestation. Three to nine days after surgery, nine fetuses had an arterial PO2 of 22 +/- 2 mmHg and O2 content of 2.68 +/- 0.65 mM. In these fetuses, the kidneys consumed O2 (107 +/- 21 mumol X min-1 X 100 g-1, mean +/- SD) and lactate (14 +/- 9.6 mumol X min-1 X 100 g-1) but produced glucose (5.6 +/- 6.5 mumol X min-1 X 100 g-1; 95% confidence limits, 0.62 and 10.5). When acute hypoxemia was induced by decreasing maternal fractional inspired O2 (FIO2) to 0.09, renal O2 consumption fell slightly (to 82 +/- 21 mumol X min-1 X 100 g-1), and there was net glucose uptake and net lactate release. A group of five fetuses was spontaneously hypoxemic 3-5 days after surgery and had an arterial PO2 of 14 +/- 2 mmHg and O2 content of 1.99 +/- 0.51 mM. Renal blood flow and O2 consumption were greater in these fetuses than in the normoxemic fetuses. There was net lactate uptake and no net flux of glucose across the renal circulation. These results demonstrate that renal metabolism of carbohydrate is altered by changes in fetal oxygenation.
Ammonia and bicarbonate transport by rat cortical collecting ducts perfused in vitro
Authors: Knepper M. A. , Good D. W. , Burg M. B.
Published: December 2017

We measured bicarbonate and ammonia transport by isolated perfused cortical collecting ducts from deoxycorticosterone-treated rats. With no ammonia in the perfusate and bath solutions, the collecting ducts secreted bicarbonate. The bicarbonate secretion was prevented when the rats were given 40 mM NH4Cl to drink. When 4 mM total ammonia was added to the perfusate and bath, the collecting ducts secreted ammonia and the direction of bicarbonate transport reversed toward absorption. Under those conditions the collected total ammonia concentration exceeded the value predicted by the diffusion-trapping model, assuming pH equilibrium. However, when carbonic anhydrase was added to the perfusate (to assure pH equilibrium), the collected total ammonia concentration decreased to the level predicted by the diffusion-trapping model. We conclude that rat cortical collecting ducts can secrete bicarbonate at substantial rates; the rate of bicarbonate secretion is modified by changes in the acid-base intake of the rats; ammonia secretion occurs by simple nonionic diffusion in this segment; the ammonia secretion is enhanced by the presence of acidic pH disequilibrium in the lumen; and ammonia in the perfusion and bath solutions inhibits bicarbonate secretion by rat cortical collecting ducts, a response that may be important for the regulation of renal bicarbonate excretion.
Erythrocyte flow and dynamic hematocrit in the renal papilla of the rat
Authors: Zimmerhackl B. , Dussel R. , Steinhausen M.
Published: December 2017

The microcirculation of the renal papilla was investigated in 32 vasa recta of Wistar rats. Using fluorescence microscopy in combination with a high-sensitivity television system we measured the velocity and flux of fluorescent-tagged erythrocytes in descending (DVR) and ascending vasa recta (AVR). After staining the plasma with fluorescent high molecular weight dextran we determined the diameters of DVR and AVR. Red cell flux (Qrbc) was determined from the ratio of the frequency of fluorescent-tagged red cells detected per unit time (fFITC) to the number of fluorescent-tagged red cells per nanoliter packed red cells (NFITC). From red cell velocity (Vrbc) and vessel diameter (D) we calculated the volume flow (Vapp). The dynamic hematocrit was directly derived as the ratio of Qrbc to Vapp. During antidiuresis Vrbc was 1.35 +/- 0.15 mm X s-1 (mean +/- SE) in DVR and 0.47 +/- 0.07 mm X s-1 in AVR. Qrbc in the same vessels averaged 3.26 +/- 0.9 and 1.72 +/- 0.35 nl X min-1, respectively. The diameter in DVR was 14.3 +/- 0.9 and in AVR 17.9 +/- 0.9 micron. From these values we calculated a dynamic hematocrit of 26 +/- 4 in DVR and 25 +/- 4% in AVR. The systemic hematocrit was 44 +/- 1%. The dynamic hematocrit in vasa recta represented 59 +/- 9 and 57 +/- 8% of the value in the systemic circulation, respectively.
Nephron site of resistance to phosphaturic effect of PTH during respiratory alkalosis
Authors: Berndt T. J. , Knox F. G.
Published: December 2017

This study was performed to evaluate the nephron site(s) responsible for the blunted phosphaturic effect of parathyroid hormone during respiratory alkalosis. In normocapnic thyroparathyroidectomized rats, parathyroid hormone administration markedly increased the fractional excretion of phosphate (FEp) from 2.1 +/- 0.5 to 36.6 +/- 5.0%. However, in the respiratory alkalotic rats, parathyroid hormone administration did not significantly increase the FEp (1.4 +/- 0.9 to 5.9 +/- 2.2%). This blunted phosphaturic response to parathyroid hormone was not due to a blunted inhibition of phosphate reabsorption by the superficial proximal tubule, since parathyroid hormone administration significantly increased the fractional delivery of phosphate (FDp) at the superficial late proximal tubule in both normal (25.3 +/- 3.0 to 36.2 +/- 3.8%, delta 10.9 +/- 3.2%) and respiratory alkalotic rats (12.2 +/- 3.1 to 30.3 +/- 4.9%, delta 18.0 +/- 4.7%). Parathyroid hormone administration significantly increased the FDp at the superficial early distal tubule from 9.3 +/- 3.9 to 38.7 +/- 7.4% (delta 29.4 +/- 5.1%) in normal rats and from 4.5 +/- 1.7 to 12.9 +/- 3.4% (delta 8.5 +/- 3.2%) in the respiratory alkalotic rats. We conclude that the blunted phosphaturic response to parathyroid hormone in respiratory alkalotic rats is not due to a blunted inhibition of phosphate reabsorption by the proximal convoluted tubule but is primarily due to enhanced reabsorption by the pars recta segment of the proximal tubule.
Effects of membrane fluidizing agents on renal brush border proton permeability
Authors: Ives H. E. , Verkman A. S.
Published: December 2017

H+ permeability (PH) of brush border membrane vesicles isolated from rabbit renal cortex was measured from the rate of collapse of preformed pH gradients using acridine orange fluorescence quenching. n-Alkanols increased PH from 0.005 to 0.1 cm/s in a dose-dependent manner. At 25 degrees C, PH increased to 0.01 cm/s at [n-alkanol] = 90 mM (butanol), 30 mM (pentanol), 7 mM (hexanol), and 1.8 mM (heptanol). Activation energy (Ea) of PH was 21.6 kcal/mol (5-50 degrees C), which decreased to 18.5 kcal/mol in the presence of either 200 mM butanol or 12 mM hexanol. Membrane fluidity was estimated from diphenylhexatriene anisotropy (r). n-Alkanols decreased r from 0.25 to 0.18 in a dose-dependent manner. At 25 degrees C, r = 0.22 at [n-alkanol] = 200 mM (butanol), 27 mM (pentanol), 9.5 mM (hexanol), and 2 mM (heptanol). The effects of n-alkanols on PH and r correlated well with known n-alkanol lipid-water partition coefficients. Similar increases in PH and decreases in r were observed for nonalkanol lipid anesthetics. The effects of n-alkanols on the Na+-H+ antiporter and on osmotically driven water transport were also studied. At concentrations of n-alkanol that resulted in a 10-fold increase in PH, there was no significant effect on either Na+-H+ exchange or water transport. These results suggest a lipid pathway for brush border H+ diffusion that is distinct from both the Na+-H+ antiporter and the water transport pathway.
Structural-functional relationships along the distal nephron
Authors: Madsen K. M. , Tisher C. C.
Published: December 2017

The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (ICT), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.
Patterns of K+ permeation following inhibition of Na+ transport in rabbit cortical collecting tubule
Authors: Stokes J. B.
Published: December 2017

The passive (lumen-to-bath) K+ permeation (KK) of rabbit cortical collecting tubules was measured before and after inhibition of Na+ transport. Inhibition of the Na-K pump with ouabain reduced KK. This result contrasts sharply with the previously described increase in KK observed following inhibition of Na+ transport with amiloride. These opposite changes in KK are owing to the fact that a substantial component of the lumen-to-bath K+ permeation involves a transcellular pathway. Amiloride, because it hyperpolarizes the apical membrane, increases KK; ouabain, because it depolarizes the cell, decreases KK. Previous results have also suggested that the cell K+ permeability is secondarily altered by these agents so that the changes in voltage and permeability are additive. These patterns of changes in KK were used to evaluate the mechanism of action of two agents that partially inhibit Na+ transport: vasopressin and prostaglandin (PG) E2. Their effect on KK was qualitatively similar to that of amiloride. In amiloride-treated tubules, neither vasopressin nor PGE2 altered KK. Neither did they alter the normal reduction in KK caused by pump inhibition. Thus they did not have any direct effect on K+ permeability. These results are consistent with the thesis that vasopressin and PGE2 inhibit Na+ absorption by reducing apical membrane permeability. The relation between the regulation of Na+ absorption and K+ permeation may have important implications for the regulation of K+ secretion by the cortical collecting tubule.