bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of fluid intake on basal and vasopressin-responsive urinary prostaglandin E
Authors: Campbell H. T. , Craven P. A. , DeRubertis F. R.
Published: December 2017

The effects of fluid intake on basal and vasopressin-responsive urinary PGE excretion (UPGEV) were examined in conscious rats under conditions of 1) ad libitum water intake, 2) water deprivation, and 3) water diuresis induced by ad libitum intake of 5% dextrose in water. UPGEV fell progressively during 40 h of water deprivation. Water diuresis after water deprivation increased UPGEV transiently (8 h). Vasopressin (Pitressin tannate in oil, 5 U/kg subcutaneously) increased UPGEV and decreased urine volume (V) in rats on ad libitum water intake but did not alter UPGEV during water deprivation. Indomethacin suppressed UPGEV (70-90%), increased basal urine osmolality (Uosmol), and potentiated the antidiuretic response to Pitressin in rats on ad libitum water intake. Indomethacin accelerated by 8 h the onset of maximal antidiuresis in water-deprived rats but did not significantly alter water balance. During water diuresis, UPGEV declined in the first 8 h after Pitressin. Thereafter, UPGEV increased markedly, concurrent with early vasopressin escape. Indomethacin or meclofenamate inhibited the rise in UPGEV, the decline in Uosmol, and the increase in V of the escape phase. Indomethacin or meclofenamate also impaired the excretion of an acute water load (5% body wt) given during escape. The spontaneous decline in UPGEV during hydropenia may serve to maximize physiologic antidiuresis. Conversely, the marked increase in UPGEV induced by administration of vasopressin during water diuresis may serve to suppress the antidiuretic response and thus play a role in the mediation of escape from physiologically inappropriate antidiuresis.
Effect of PGE2 on vasopressin-dependent cell cAMP in isolated single nephron segments
Authors: Torikai S. , Kurokawa K.
Published: December 2017

To further evaluate the interaction between vasopressin (AVP) and prostaglandin E2 (PGE2) in the kidney, the effects of AVP and PGE2 on cell cAMP content were examined in the isolated thick ascending limb of Henle (TAL) and the cortical collecting tubule (CCT) of rat kidney. Nephron segments were incubated in the presence of phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), with 10 nM AVP and varying concentrations of PGE2 at 37 degrees C for 1-7 min, and the cAMP content was determined by radioimmunoassay. PGE2 suppressed the AVP-stimulated increase in cell cAMP in both medullary (MTAL) and cortical (CTAL) portions of the TAL in a dose-dependent manner. This inhibitory effect was evident at 0.28 nM PGE2 and maximum at 2.8-28 microM PGE2. By contrast, in the presence of MIX PGE2 did not inhibit AVP-stimulated cAMP increases in the CCT. However, in the absence of MIX, PGE2 suppressed cAMP accumulation in the CCT. These data suggest that PGE2 may suppress cell cAMP by inhibiting AVP-dependent cAMP formation in the TAL; PGE2 may suppress cAMP in the CCT by acting at a site(s) affected by MIX and not by inhibiting cAMP formation. The results show that although PGE2 may inhibit AVP-dependent cell cAMP accumulation in both TAL and CCT, the underlying cellular mechanisms may be different in these two distinct AVP-sensitive nephron segments.
Effects of mineralocorticoids on Na+ and K+ excretion in the adrenalectomized rat
Authors: Horisberger J. D. , Diezi J.
Published: December 2017

The short-term effects (within 4 h) of low doses of intravenous aldosterone or deoxycorticosterone on potassium and sodium urinary excretion were studied by clearance techniques in 24-h adrenalectomized, anesthetized male rats. All animals were substituted with a glucocorticoid (dexamethasone; plasma concentration approximately 6 nM) to maintain normal glomerular filtration rate. The mineralocorticoid effects were studied under various conditions of sodium and potassium load. Mineralocorticoid administration uniformly resulted in antinatriuresis, starting within 30-60 min and, at the peak effect, amounting to 1-2% sodium fractional excretion. The level of antinatriuresis was directly related to the control sodium excretion before aldosterone administration. Mineralocorticoids induced a significant kaliuresis in all groups except one, the one receiving the lowest sodium load. The aldosterone-induced kaliuresis was also related to the sodium load and the control fractional sodium excretion level and was simultaneous with the beginning of the reduced sodium excretion. In control, mineralocorticoid-deprived rats, kaliuresis was not enhanced by increasing the sodium load. Control as well as mineralocorticoid-treated rats responded by an increased kaliuresis following an acute potassium load and by a decreased kaliuresis after 3 days of low potassium diet.
Effects on renal hemodynamics of intra-arterial infusions of angiotensins I and II
Authors: Rosivall L. , Navar L. G.
Published: December 2017

Experiments were conducted in anesthetized dogs to evaluate the differences between the effects of intrarenal conversion of angiotensin I (ANG I) to angiotensin II (ANG II) and those of circulating ANG II on renal blood flow (RBF), glomerular filtration rate (GFR), peritubular capillary pressure (PCP), proximal tubular free-flow pressure (PTP), and stop-flow pressure (SFP). Equiconstrictor doses of ANG I and ANG II were infused into the renal arteries of dogs kept on normal and high sodium diets. In clearance experiments, RBF decreased by 23% (low dose) and 33% (high dose) during the infusion of either ANG I or ANG II; GFR was significantly reduced only during the ANG I infusion. In micropuncture experiments, in which the GFR responses were similar, there were significant reductions in PTP (23 +/- 3%) and PCP (33 +/- 3%) during the intrarenal ANG I infusion; SFP was not altered significantly. Afferent and efferent arteriolar resistances increased significantly during ANG I infusion as well as during infusion of ANG II. These results indicate that during intra-arterial infusion of ANG I, the conversion to ANG II within the kidney occurs early enough to decrease glomerular filtration rate through an apparent increase in preglomerular resistance.
Fluidity of brush border and basolateral membranes from human kidney cortex
Authors: Le Grimellec C. , Carriere S. , Cardinal J. , Giocondi M. C.
Published: December 2017

The physical state of lipids in brush border and basolateral membrane vesicles prepared from normal human kidney cortex was investigated by fluorescence polarization and electron spin resonance. At physiologic temperature, lipids were significantly less ordered, i.e., more fluid, in basolateral than in brush border membranes. This difference was also observed using corresponding liposomes made from total lipid extracts. For both brush border and basolateral membranes, temperature-dependent experiments revealed the existence of a broad thermotropic transition extending approximately from 20 to 42 degrees C. These data are interpreted to indicate that plasma membranes from human kidney cortex function physiologically at the upper critical temperature of a transition that probably corresponds to a liquid crystalline-to-gel lipid phase separation.
Volume expansion predominantly inhibits proximal reabsorption of NaCl rather than NaHCO3
Authors: Cogan M. G.
Published: December 2017

The present study quantitated the effect of extracellular volume expansion on absolute proximal bicarbonate, chloride, and water reabsorption in 10 Sprague-Dawley rats. Paired free-flow micropuncture measurements were made in the plasma-replete euvolemic state and following 10% body wt isohydric, colloid-free volume expansion. Single nephron glomerular filtration rate and glomerular ultrafiltrate concentration of bicarbonate and chloride were similar in the two conditions. Volume expansion caused absolute proximal reabsorption of bicarbonate to fall by only 7% (from 987 +/- 39 to 920 +/- 53 pmol/min, P less than 0.05). This decrement in bicarbonate reabsorption was compatible with the known increase in bicarbonate permeability and backleak induced by expansion. In contrast, a marked 26% fall in absolute proximal chloride reabsorption occurred (from 1,601 +/- 147 to 1,180 +/- 149 peq/min, P less than 0.005), attributed to alteration in transcellular rather than passive sodium chloride transport. Thus, the decrease in absolute proximal volume reabsorption (from 19.7 +/- 1.0 to 16.7 +/- 1.2 nl/min, P less than 0.005) induced by volume expansion was predominantly a consequence of inhibition of sodium chloride rather than sodium bicarbonate reabsorption.
Effects of ouabain and furosemide on basolateral membrane Na efflux of frog skin
Authors: Cox T. C. , Helman S. I.
Published: December 2017

The kinetics of Na tracer fluxes were reinvestigated in isolated epithelia of frog skin in which the unstirred layers of the corium were removed. The rate of appearance of 22Na in the basolateral solution (JNa13) conformed to a single exponential for tracer buildup with a mean t1/2 of 1.9 min. The Na transport pool labeled isotopically from the apical solution was about 40 neq/cm2 for epithelia bathed in either a chloride or sulfate Ringer solution. Basolateral-to-apical solution unidirectional Na flux (JNa31) was low, averaging 0.7 microA/cm2 and remained low for 40 min of ouabain treatment of the epithelia. In agreement with electrophysiological data, ouabain at 10(-4) M caused an acute inhibition (less than 1 min) of the Na efflux at the basolateral membrane (JNa23), falling to 40.6 and 26.7% of control for epithelia bathed in Cl and SO4 Ringer, respectively. Although furosemide exerted little or no consistent effect on the Na flux of control epithelia, this drug in ouabain-poisoned epithelia caused a substantial inhibition of a neutral, chloride-dependent, ouabain-insensitive Na efflux. It is suggested that ouabain "induces" a neutral mechanism of Na transport at the basolateral membrane of the cells that is chloride dependent and furosemide sensitive.
On the generation, maintenance, and correction of metabolic alkalosis
Authors: Jacobson H. R. , Seldin D. W.
Published: December 2017

The study of derangements in salt, water, and acid-base homeostasis frequently reveals much about renal transport mechanisms and their regulation. The study of one such derangement, metabolic alkalosis, has played a special role in contributing to our knowledge of renal function. Elucidation of the kidney's role in the generation, maintenance, and correction of metabolic alkalosis has provided information about proximal tubule transport and its response to volume contraction, volume expansion, and K depletion. Also, distal nephron transport and its response to mineralocorticoids and dietary anion composition has been clarified by studies on metabolic alkalosis. Finally, we have learned about the importance of Na delivery to distal nephron sites and the avidity with which these distal nephron sites reabsorb sodium. Indeed, reviews on the subject of metabolic alkalosis have presented thorough and convincing physiologic arguments on how the kidney helps to generate and maintain this derangement in acid-base balance. However, more recent experimental work has led some to reconsider how the kidney functions in metabolic alkalosis. In an earlier paper in this journal [Am. J. Physiol. 244 (Renal Fluid Electrolyte Physiol. 13): F217-F221, 1983], Galla, Bonduris, and Luke present an argument for the correction of chloride-depletion alkalosis in the rat without volume expansion.(ABSTRACT TRUNCATED AT 250 WORDS)
Determination of glomerular permselectivity to neutral dextrans in the dog
Authors: Whiteside C. , Silverman M.
Published: December 2017

The multiple-indicator-dilution (MID) technique was used to separate solute flux (Js) across the glomerular and postglomerular capillaries in vivo. Anesthetized mongrel dogs (n = 20) during mannitol diuresis received a pulse of extracellular indicators including 125I-albumin (plasma reference), [14C]inulin (glomerular reference), creatinine (interstitial reference), and a neutral [3H]dextran (specific mol wt between 10,000 and 24,000 dalton) in the left renal artery. Left renal venous and ureteric outflows were rapidly sampled. 3H-labeled dextrans 10,000-15,500 had renal vein mean transit times (t) greater than those of 125I-albumin, indicating postglomerular extraction. 3H-labeled dextrans greater than 15,500 had t values identical to those of 125I-albumin, indicating only unidirectional glomerular extraction. The glomerular fractional dextran extractions relative to simultaneously injected [14C]inulin (ED/Ei) were calculated from urine and renal vein outflow curves and ranged from 0.98 +/- 0.02 to 0.33 +/- 0.12 (SD) for mol wt 10,000 +/- 24,000. ED/Ei values were quantitatively identical to constant-infusion fractional clearances of the same dextrans. Renal plasma flow (RPF) was then deliberately reduced two-to threefold in the same dog. ED/Ei as measured by the MID technique remained unchanged during graded reduction in RPF. In constant-infusion experiments RPF was reduced from 5.78 to 2.77 ml X s-1 X 100 g-1 and GFR from 50.4 to 36.3 ml X min-1, but the fractional neutral dextran clearances remained constant. The predominance of convective solute flux across the dog glomerulus permitted calculation of glomerular reflection coefficients 0.03 +/- 0.06 to 0.85 +/- 0.03 (SD) for neutral 3H-labeled dextrans 10,000-24,000 dalton.
Contribution of vasopressin to the maintenance of blood pressure during dehydration
Authors: Woods R. L. , Johnston C. I.
Published: December 2017

Normal Long-Evans rats, when dehydrated for up to 72 h, have a progressive rise in plasma vasopressin that is associated with a fall in body weight and urine volume, a rise in plasma and urine osmolality, and the maintenance of normal systolic blood pressure. In contrast, Brattleboro diabetes insipidus rats, genetically deficient in vasopressin, when dehydrated to achieve an equivalent body weight loss, have a significant 15 mmHg fall in systolic blood pressure. Even when fluid balance is corrected in the Brattleboro rats by the continuous administration of 1-desamino-8-D-arginine vasopressin, a synthetic vasopressin analogue with potent antidiuretic properties but minimal pressor activity, blood pressure still falls when the animals are dehydrated. In contrast, Brattleboro rats infused with exogenous arginine vasopressin to produce a plasma vasopressin level of 18.9 +/- 3.5 pg X ml-1 are able to maintain normal blood pressure during 48 h of dehydration. This level of vasopressin is comparable to the level found endogenously in dehydrated Long-Evans rats and is nonpressor in normal rats. These results suggest that both the antidiuretic and vasoconstrictor properties of vasopressin are important in the cardiovascular response to dehydration.
Handling of ammonium by the renal proximal tubule during acute metabolic acidosis
Authors: Simon E. , Martin D. , Buerkert J.
Published: December 2017

The present studies were designed to assess the handling of ammonium (NH+4) by the proximal tubule during acute metabolic acidosis (AMA). After tubule fluid collections were obtained with micropuncture techniques and in situ pH was determined near the end of the proximal tubule, 0.2 N HCl was infused intravenously at 17 microliter X min-1 X 100 g body wt-1. Thirty to sixty minutes later, samples were obtained and pH measurements were made near the previous micropuncture sites. During AMA, urine pH fell and total acid excretion doubled due to an increase in NH+4 excretion from 581 +/- 63 to 1,153 +/- 61 nmol X min-1 X g kidney wt-1 (P less than 0.001). Acid excretion did not change in time controls. Tubule fluid NH+4 rose from 2.17 +/- 0.15 to 3.45 +/- 0.24 mM during acid infusion (P less than 0.001) and its delivery to the end of the proximal tubule nearly doubled (67.8 +/- 6.3 vs. 33.9 +/- 2.9 pmol X min X g kidney wt-1 before acid infusion, P less than 0.001). This increase in delivery during AMA was due to enhanced ammonia (NH3) entry into the proximal tubule. In situ pH determined near the end of the proximal tubule averaged 6.94 +/- 0.04 before acid infusion and did not change afterwards (6.87 +/- 0.05). These data are consistent with the hypothesis that in AMA the increase in NH+4 excretion is due primarily to an increase in the cortical production of NH3.
Electrochemical heterogeneity of the cochlear endolymph: effect of acetazolamide
Authors: Sterkers O. , Saumon G. , Tran Ba Huy P. , Ferrary E. , Amiel C.
Published: December 2017

The electrochemical composition of endolymph (EL) of two adjacent cochlear turns was studied in anesthetized rats. Differences in [K]EL, [Cl]EL, and endocochlear potential (EP) were found between the basal turn (165.6 +/- 3.0 mM, n = 14; 144.6 +/- 2.1 mM, n = 14;96.6 +/- 1.9 mV, n = 5, respectively) and the middle turn (155.7 +/- 2.5 mM, n = 15; 133.2 +/- 1.5 mM, n = 15; 87.0 +/- 1.6 mV, n = 6, respectively). The pH values of inner ear fluids were evaluated with 5,5-dimethyloxazolidine-2,4-dione: EL pH of either turn was not different from blood and perilymph (PL) pH. Acetazolamide (40 mg X kg body wt-1) reduced EP and [Cl]EL at each turn by about 20 and 6%, respectively, but [K]EL was unchanged. The electrochemical differences between the two turns persisted. Acetazolamide produced a 0.2-unit decrease in blood pH while the pH values of EL and PL remained unchanged. These results suggest the existence of an electrochemical gradient within EL from the base to the apex of the cochlea involving K+ and Cl- concentrations. H+ and HCO-3 do not appear to participate in this gradient, and the acid-base status in EL could be maintained both by active H+ transport into EL and by HCO-3 formation in the cochlear epithelium.
Effect of pH on the permeability of the distal nephron to prostaglandins E2 and F2 alpha
Authors: Peterson L. N. , Gerber J. G. , Nies A. S.
Published: December 2017

Because PGE2 and F2 alpha are derivatives of arachidonic acid, the effect of pH on dissociation of the carboxyl group would be expected to alter the lipid solubility of these substances and consequently their efflux from the distal nephron. To assess this possibility on the single nephron level, 20-nl samples of chromatographically pure [3H]prostaglandins were microinjected into early distal tubules and their recovery was compared with that of [14C]insulin in rats undergoing osmotic diuresis with NaHCO3 or Na2SO4 containing HCl. Although urine flow rates were similar, there was a striking elevation of urine pH in bicarbonate-loaded rats (7.87 +/- 0.017 vs. 5.66 +/- 0.067). To examine luminal factors acting on prostaglandin movement, collections of early distal fluid were made and total [CO2] was measured by microcalorimetry. There was no difference in distal flow rate, whereas total [CO2] and calculated pH were significantly elevated in the bicarbonate-loaded rats (7.66 +/- 0.029 vs. 6.07 +/- 0.093). We found that tubular efflux of both prostaglandins from the distal nephron is very small as the maximum efflux measured in acid-loaded rats was only 4% of the injected quantity. However, there was no efflux of PGE2 when microinjection was made into distal tubules of bicarbonate-loaded animals. All isotope excreted in the urine was the unchanged parent prostaglandin and both prostaglandins were coexcreted with inulin for all injections in bicarbonate- and acid-loaded animals. These results suggest that permeability of the distal nephron to PGE2 and F2 alpha is normally very low. Nevertheless, permeability of PGE2 can be further reduced when urine pH is elevated.
Renal potassium adaptation in the rat: role of glucocorticoids and aldosterone
Authors: Adam W. R. , Goland G. J. , Wellard R. M.
Published: December 2017

This study examines the role of adrenocortical hormones in the kaliuresis following an acute intragastric KCl load in conscious control (CK) and high potassium diet (HK) rats. Adrenalectomy, 1 day before test, reduced K+ excretion by 35% in CK and 60% in HK rats, leading to minimal differences in K excretion between CK and HK. By contrast, spironolactone inhibited K excretion by only 10%. Glucocorticoids (dexamethasone 3-10 micrograms/100 g) increased K+ excretion in adrenalectomized CK and to a greater extent in adrenalectomized HK rats. Aldosterone (3 micrograms/100 g) alone had a variable effect on urinary potassium excretion in adrenalectomized rats. A combination of dexamethasone (3 micrograms/100 g) and aldosterone (3 micrograms/100 g) in adrenalectomized rats induced potassium excretion equivalent to that in intact rats. Adrenalectomized HK rats had a greater kaliuretic response to dexamethasone and aldosterone than CK rats. These results 1) demonstrate a role for glucocorticoids in K+ excretion in HK rats and 2) illustrate the importance of the increased responsiveness to both glucocorticoids and mineralocorticoids in potassium adaptation.
Properties of an anion exchanger in rat renal basolateral membrane vesicles
Authors: Low I. , Friedrich T. , Burckhardt G.
Published: December 2017

Sulfate uptake in basolateral membrane vesicles from rat kidney cortexes was studied to test for the presence of an anion exchanger in these membranes. A pH difference (pHout = 6.4, pHin = 8.4) and a sodium gradient (out greater than in, pHout = pHin = 7.4) provided the driving force for intravesicular sulfate accumulation above the equilibrium content ("overshoot"). Sulfate uptake in vesicles preloaded with 25 mM of sulfate, thiosulfate, phosphate, chloride, or bicarbonate, or 10 mM of formate, acetate, L-lactate, pyruvate, p-aminohippurate, or oxalate was stimulated with respect to uptake in unpreloaded vesicles. Probenecid inhibited these trans stimulations. When the uptake of 0.1 mM labeled sulfate was determined in the presence of 5 mM of various anions in the incubation medium, cis inhibitions were observed when sulfate was driven by a proton gradient (out greater than in), a sodium gradient (out greater than in), or a p-aminohippurate gradient (in greater than out). All anions that trans stimulated sulfate uptake also showed a cis inhibition. Only small cis inhibitions were seen with maleate and succinate. No inhibition by any of the anions was found when sulfate uptake was studied in the absence of driving cation or anion gradients. Our data indicate a common exchanger for inorganic and organic anions that can additionally be driven by a sodium gradient and a pH difference. This exchanger may be involved in reabsorption and secretion of anions in the proximal tubule of the rat kidney.
Renal adaptation to phosphate load in the acutely thyroparathyroidectomized rat: rapid alteration in brush border membrane phosphate transport
Authors: Cheng L. , Dersch C. , Kraus E. , Spector D. , Sacktor B.
Published: December 2017

The sustained in vivo infusion of phosphate into thyroparathyroidectomized rats resulted, after 1 h, in a marked decrease in net phosphate reabsorption, even though the plasma concentration of phosphate continued to rise. This response to phosphate infusion was expressed at the level of the proximal tubule brush border membrane. Within 40 min of the initiation of the infusion the Na+-dependent phosphate uptake system in isolated membrane vesicles was decreased. Phosphate uptake in the absence of Na+, Na+-dependent D-glucose uptake, and 22Na+ uptake were not affected. These findings demonstrate the locus of this parathyroid hormone-independent adaptation and indicate the rapidity with which the membrane transport system is regulated.
Effect of aldosterone on abundance and phosphorylation kinetics of Na-K-ATPase of toad urinary bladder
Authors: Park C. S. , Edelman I. S.
Published: December 2017

The possibility was explored that aldosterone-dependent modulation of either the abundance or the kinetic properties of the Na+ pump (Na-K-ATPase) is involved in the mechanism of natriferic action on toad urinary bladder. Cell membranes from the epithelium of urinary bladders of toads were prepared by a sucrose-Ficoll step gradient method, which yielded a 10-fold increase in specific activity of plasma membrane marker enzymes and only minor contamination with other subcellular fractions. Phosphorylation of Na-K-ATPase by gamma-PO4 of [gamma-32P]ATP in the presence of Mg2+ was Na+ dependent, whereas dephosphorylation was K+ dependent. Km for phosphorylation by ATP was 3 X 10(-8) M and K1/2 (half-maximal stimulation) for Na+ was 13 +/- 2 mM. Pretreatment of cell membranes with sodium deoxycholate (DOC) increased the maximal extent of phosphorylation (Nmax) about threefold without changing the Km for ATP. Aldosterone (5 X 10(-8) M) stimulated transepithelial Na+ transport two- to threefold in 5 h but had no significant effect on Km for ATP in the phosphorylation reaction (with or without activation by DOC) or on the abundance of the enzyme inferred from Nmax of phosphorylation in the absence of activation by DOC. After pretreatment with DOC, average Nmax was 13% greater in the aldosterone-treated population. Regression analysis of these responses revealed no significant correlation between increments in short-circuit currents and Nmax values of phosphorylation with or without pretreatment with DOC.(ABSTRACT TRUNCATED AT 250 WORDS)
Derangements of muscle composition, ion transport, and oxygen consumption in chronically alcoholic dogs
Authors: Ferguson E. R. , Blachley J. D. , Carter N. W. , Knochel J. P.
Published: December 2017

Muscle ion composition, Na-K-ATPase activity, tissue respiration, and transmembrane potential differences were measured after 28 and 56 days of ethanol consumption (6.2 g X kg-1 X day-1) or an isocaloric amount of glucose in 12 and 4 dogs, respectively. Ethanol and glucose were given as supplements to an otherwise nutritious diet. After 28 and 56 days of alcohol consumption, skeletal muscle contents of phosphorus, magnesium, and potassium were significantly reduced as compared with either the control values or those in glucose-fed animals. In alcohol-fed animals, muscle sodium chloride, and calcium were significantly elevated. Ethanol consumption also resulted in hyperpolarization of the resting transmembrane potential of skeletal muscle fibers and a significant increase in Na-K-ATPase activity. No change was noted in Mg-ATPase activity. The increase in Na-K-ATPase activity was accompanied by increased sodium transport-dependent respiration. These results indicate that a subclinical myopathy may be induced by alcohol in the dog. Malnutrition did not appear to be a factor in this study, and thus the changes observed are believed to be due to ethanol per se. The magnitude and direction of these changes are similar to those observed in the skeletal muscle of chronically alcoholic humans. The changes in Na-K-ATPase activity and sodium transport-dependent respiration may represent adaptive responses of the muscle cell to ion transport or membrane disorders induced by ethanol.
Adenosine transport in perfused rat kidney and renal cortical membrane vesicles
Authors: Trimble M. E. , Coulson R.
Published: December 2017

Adenosine is a modulator of renal function but little is known about transport of this compound by renal tubular cells. Transport of exogenous adenosine was studied in isolated perfused rat kidney and in luminal (L) and antiluminal (AL) membrane vesicles isolated from rat renal cortex. Most experiments were performed in the presence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine. Kidneys were perfused in a recirculating system with Krebs-Henseleit bicarbonate buffer containing 6 g albumin/dl and adenosine. Net secretion of adenosine occurred at perfusate adenosine concentrations greater than 40 microM, and net reabsorption was seen at concentrations less than 40 microM. N6-(L-2-phenylisopropyl)adenosine (PIA), a nondeaminated adenosine receptor agonist, also showed net reabsorption when unbound PIA concentrations were 10-20 microM. Influx or efflux of [3H]adenosine in vesicles was measured using a rapid filtration technique. Transport into both L and AL vesicles was saturable. L vesicles demonstrated both high Km (43 +/- 4 microM) and low Km (4.4 +/- 0.6 microM) transport systems. Only a low Km (5 +/- 1 microM) system could be demonstrated in AL vesicles. Results indicate that at concentrations in the physiological range (less than 1 microM) adenosine undergoes mediated transport across both L and AL membranes and that net transport across the L membrane is in the direction of reabsorption.
Role of prostaglandins in renin secretion in the isolated kidney
Authors: Linas S. L.
Published: December 2017

Prostaglandins (PG) stimulate renin secretion through a mechanism that does not require activation of the intrarenal vascular, macula densa (MD), or beta-adrenergic receptors. In the present study the isolated perfused rat kidney was used to study the role of PG as a mediator of renin secretion when extracellular calcium was decreased and after activation of each of the intrarenal receptors. A decrease in extracellular calcium resulted in an increase in renin (from 2.1 to 4.5 ng ANG I/ml, P less than 0.01) and a decrease in PGE2 excretion (from 102 to 44 pg X min-1 X g-1, P less than 0.01). PG synthesis inhibition with indomethacin did not attenuate the increase in renin secretion. Following beta-receptor stimulation with isoproterenol, there was an increase in renin (from 2.1 to 6.6 ng ANG I/ml, P less than 0.01) not associated with changes in PGE2 excretion and not prevented by PG inhibition. When the isolated vascular receptor was stimulated by perfusing either filtering or nonfiltering kidneys below the autoregulatory range of pressure, both renin and PGE2 production were increased, and the increases were prevented by PG inhibition. The MD was activated by three methods: eliminating distal nephron fluid delivery by perfusing with hyperoncotic albumin; perfusing at 60 mmHg in the presence of papaverine; and limiting chloride transport by partially replacing chloride with nitrate in the perfusate. In each circumstance renin and PGE2 production were increased and the increase was prevented by PG inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanism of bicarbonate exit across basolateral membrane of the rabbit proximal convoluted tubule
Authors: Sasaki S. , Berry C. A.
Published: December 2017

To clarify the mechanism(s) of HCO-3 movement across the basolateral membrane, rabbit proximal convoluted tubules were perfused in vitro. Two possible mechanisms were examined: neutral HCO-3 exit coupled to chloride and rheogenic HCO-3 exit. A complete C1- substitution with isethionate in the lumen and bath did not affect HCO-3 reabsorption, suggesting that HCO-3 exit is not coupled to chloride. Addition of 2 mM Ba2+ to the bath, which has been shown to depolarize the basolateral membrane potential difference, caused a 42% inhibition of HCO-3 reabsorption and a 32% inhibition of volume flux, suggesting that HCO-3 exit is rheogenic. Ba2+ did not affect the volume flux when HCO-3 reabsorption was inhibited by acetazolamide, suggesting that the Ba2+ effect is not due to a general inhibition of cell metabolism. From these data we propose that HCO-3 exits the basolateral membrane by a rheogenic, chloride-independent mechanism.
Potassium transport by flounder intestinal mucosa
Authors: Frizzell R. A. , Halm D. R. , Musch M. W. , Stewart C. P. , Field M.
Published: December 2017

We studied the mechanisms of K transport across an epithelium in which NaCl absorption is mediated primarily by Na/K/Cl cotransport at the apical membrane. Rubidium served as a reliable K substitute; under control conditions, both K and Rb were actively secreted. During secretion, K (Rb) enters across the basolateral membrane via the Na/K pump and exits across the apical membrane through K conductance pathways, since serosal ouabain or mucosal barium abolished K secretion, mucosal furosemide or Cl-free media blocked K secretion by interfering with access of Na to the pump, and elevated mucosal solution [K] or [Rb] depolarized the apical membrane electrical potential difference. Mucosal Ba unmasked active Rb absorption that could be blocked by mucosal furosemide. These findings illustrate active K absorption and secretion across an epithelium that comprises a single cell type in which opposing K fluxes across the apical membrane are mediated by Na/K/Cl cotransport entry and conductive K exit. The direction of transepithelial K transport is determined by the relative activities of these pathways.
Hyperosmolality of absorbate from isolated rabbit proximal tubules
Authors: Barfuss D. W. , Schafer J. A.
Published: December 2017

Rabbit proximal convoluted (PCT) and proximal straight tubules (PST) were perfused under oil so that droplets of absorbate could be collected. When PCT segments were perfused with an ultrafiltrate of rabbit serum or with a similar artificial solution, the osmolality of the absorbate was higher than that of the luminal perfusate by, respectively, 18.4 +/- 1.8 (SE) (P less than 0.001) or 15.8 +/- 1.9 (P less than 0.001) mosmol/kg H2O. In the PST, the absorbate osmolality was 7.7 +/- 2.6 mosmol/kg H2O (P less than 0.012) higher than an artificial perfusate solution. In the PCT the volume absorption rate was positively correlated with the osmolality difference (r = 0.653, P less than 0.002), and the slope of the linear regression line was 0.068 +/- 0.007 nl X min-1 X mm-1 X (mosmol/kg H2O)-1. Although a complete analysis based on reflection coefficients of the several solutes could not be made, this slope indicates that the maximum osmotic water permeability of the PCT in these experiments was 800-1,000 micron/s, which is significantly less than observed previously in tubules perfused in an aqueous bathing medium. The size of the osmotic gradient in the PST also implies a lower water permeability than expected. The results show, however, that a hyperosmotic absorbate can be generated by both segments when the peritubular volume is restricted. In vivo the same process would be expected to generate luminal hypotonicity.
Ammonia and bicarbonate transport by thick ascending limb of rat kidney
Authors: Good D. W. , Knepper M. A. , Burg M. B.
Published: December 2017

Ammonia and bicarbonate transport by the thick ascending limb of rat kidney was studied to determine whether this segment contributes to the regulation of renal ammonia and net acid excretion. Cortical and medullary thick ascending limbs were perfused in vitro at 1.0-1.5 nl X min-1 X mm-1 with HCO3-buffered solutions. There was no significant net fluid transport. With 4 mM ammonia in bath and perfusate, transepithelial voltage averaged 6-9 mV, lumen positive, and did not differ between the two segments. The mean ammonia concentration in collected tubule fluid was 2.8 mM with cortical segments and 2.3 mM with medullary segments, indicating net absorption of ammonia. Furosemide (10(-4) M) in the perfusate eliminated ammonia absorption in medullary thick ascending limbs and converted net absorption to net secretion in cortical thick ascending limbs. Furosemide reduced transepithelial voltage to near zero in every tubule. Cortical and medullary thick ascending limbs also absorbed bicarbonate, indicating that their tubule fluid was acidified relative to the bath. Therefore, absorption of ammonia could not have occurred by nonionic diffusion. The absorption most likely was due to direct transport of NH4+. The possible mechanisms involved are discussed, and it is proposed that absorption of ammonia by thick ascending limbs provides a source for its accumulation in the renal medulla and secretion into the collecting ducts.
Tachyphylaxis to PTH in the isolated perfused rat kidney: resistance of anticalciuria
Authors: Besarab A. , Swanson J. W.
Published: December 2017

Downregulation of renal responses to amino-terminal 1-34 parathyroid hormone (PTH) was studied in the isolated perfused rat kidney. PTH induced a sigmoid dose-response relationship in phosphate and urinary cAMP excretion over the concentration range 0.2-36 nM. Renal responses to a second maximally phosphaturic PTH concentration following variable initial PTH concentrations showed tachyphylaxis of both phosphate and urinary cAMP excretion but not of decreased calcium excretion. The sigmoid relationship between integrated phosphate and cAMP excretion was shifted to the right during tachyphylaxis. Administration of a maximal phosphaturic PTH dose prevented any effect on phosphate or cAMP excretion of an equivalent or smaller PTH dose administered 1 h later. Anticalciuria, however, was prolonged by the second dose. These studies indicate that downregulation in the kidneys is restricted to the phosphaturic and urinary cAMP responses but not to the anticalciuric response. They also suggest that the nephron site mediating anticalciuria behaves differently with respect to hormone-receptor interactions from those sites mediating phosphaturia.
Acid phosphatase activity in the mammalian nephron
Authors: Olbricht C. J. , Garg L. C. , Cannon J. K. , Tisher C. C.
Published: December 2017

Lysosomal acid phosphatase (AcPase) activity was measured in individual segments of rat and rabbit nephrons employing 4-methylumbelliferyl phosphate as the substrate. Generation of reaction product was linear with incubation time up to 127 min and with tubule length. Activity was much higher in glomeruli and proximal tubules of rat than rabbit kidney. In both rat and rabbit there were higher activities in juxtamedullary than in superficial glomeruli. In rats, AcPase activity decreased from S1 to S3 segments, which parallels the known decrease in the number of lysosomes. Surprisingly, in rabbits of both sexes AcPase activity in the cortical collecting duct (CCD), which contains a limited number of lysosomes, was comparable to levels measured in the S1 and S2 segments of the proximal tubule. Similarly, in the male rat values for AcPase activity in the cortical thick ascending limb, distal convoluted tubule, CCD, and medullary collecting duct paralleled those in the S3 segment. These findings suggest that a considerable amount of AcPase in the distal nephron is either extralysosomal or that the amount of lysosomal AcPase activity per unit volume is greater in distal nephron segments compared with the proximal tubule. Different K'm values for AcPase in S1 segments and CCD were found in the rabbit, suggesting the presence of different isoenzymes.
Effects of pH, calcium, and succinate on sodium citrate cotransport in renal microvilli
Authors: Barac-Nieto M.
Published: December 2017

Sodium-dependent citrate uptake (v) by rabbit renal brush border vesicles was studied as a function of pH and Ca2+, citrate, and succinate concentrations to evaluate the hypothesis that factors which alter renal citrate reabsorption also alter v. At pH 8 a 10-fold increment in citrate concentration (up to 3.3 mM) was required to achieve the same v observed at pH 7. This provides proof that the protonated citrates are the effective substrates for v. At higher citrate concentrations (5-10 mM) and pH 8, substrate inhibition of v occurred. Studies of the substrate concentration dependency of v at various pH levels and calcium concentrations indicated that v was competitively inhibited by citrate3-. Changes in calcium concentrations altered v by altering the protonated citrate and citrate3- concentrations; v showed countertransport with succinate. Sodium-dependent succinate uptake (vs) was not pH dependent but was more inhibited by 1 mM citrate at pH 7 than at pH 8, indicating that the protonated citrates are inhibitors of vs. However, citrate3- was also found to inhibit vs. Thus, changes in v at the brush border membrane due to the effects of pH or calcium concentration on the protonated citrate concentration and to competition between polycarboxylates may be relevant to changes in renal citrate reabsorption in vivo.
Protection of mitochondrial function by mannitol in ischemic acute renal failure
Authors: Schrier R. W. , Arnold P. E. , Gordon J. A. , Burke T. J.
Published: December 2017

The effect of isotonic mannitol to provide protection against ischemic renal injury was examined in the dog. Mannitol treatment attenuated the fall in glomerular filtration rate at both 1 and 24 h after the ischemic insult. The functional changes were associated with profound cellular protection, since normal mitochondrial respiration, mitochondrial calcium uptake and release rates were preserved, and excessive mitochondrial calcium accumulation was prevented. These effects at the cellular level appear critical to the protective effect of mannitol after ischemia and are most likely due to prevention of cell swelling.
In situ PCO2 in the renal cortex, liver, muscle, and brain of the New Zealand white rabbit
Authors: Hogg R. J. , Pucacco L. R. , Carter N. W. , Laptook A. R. , Kokko J. P.
Published: December 2017

Recent studies have shown that in situ PCO2 in rat renal cortical structures far exceeds systemic arterial PCO2. These results were opposite to previous assumptions that renal proximal tubule fluid PCO2 approximated arterial PCO2. The present studies examined the species and organ specificity of the elevated PCO2 in 39 New Zealand White rabbits studied under normal acid-base conditions. In situ PCO2 was measured in renal cortex, superficial hepatic parenchyma, skeletal muscle, superficial cerebral cortex, and femoral nerve, artery, and vein. The results showed rabbit renal cortical PCO2 (57.2 +/- 1.2 mmHg) to be higher than both systemic arterial (39.1 +/- 2.0 mmHg) and venous PCO2 (45.4 +/- 2.1 mmHg). Similarly, liver PCO2 (64.1 +/- 3.5 mmHg) was found to be significantly higher than systemic arterial and venous PCO2 and also higher than portal and hepatic vein PCO2. Skeletal muscle, cerebral cortex, and femoral nerve PCO2 levels were usually greater than systemic arterial PCO2 but less than systemic venous PCO2. These observations show that in situ PCO2 is significantly elevated above afferent and efferent blood PCO2 in the kidney and liver but not in muscle or brain. A possible explanation for these findings in the former two organs may be high CO2 production and/or trapping of CO2 by their vascular systems.
Ischemic acute renal failure in the rat: protective effect of uninephrectomy
Authors: Fried T. A. , Hishida A. , Barnes J. L. , Stein J. H.
Published: December 2017

Experiments were performed to investigate the effect 2-wk prior nephrectomy has on the recovery from a 40-min renal artery occlusion. Two groups were initially examined. Group 1 animals underwent sham nephrectomy and group 2 animals right nephrectomy 14 days prior to a 40-min left renal artery clamp. The percent recovery of inulin clearance in group 2 (33 +/- 6%) was not significantly different from that in the group 1 (36 +/- 8%) when measured 3 h after reflow. At 24 and 48 h of reflow, however, group 2 animals had a significantly higher percent recovery of inulin clearance (24 h: 31 +/- 5%; 48 h: 50 +/- 11%) than group 1 animals (24 h: 1 +/- 1%; 48 h: 8 +/- 4%). Similarly the histology was better preserved at 24 and 48 h in group 2. To further investigate this enhanced recovery, three additional groups were studied. Group 3 underwent right nephrectomy at the time of renal artery occlusion. Group 4 had right uretero-venostomies created immediately prior to the ischemic insult, and group 5 had their aortas rather than left renal arteries clamped. Each group shared with group 2, ischemia to all functioning excretory tissue. The percent recovery of inulin clearance in group 3 (48 +/- 9%), group 4 (54 +/- 5%), and group 5 (42 +/- 6%) were each significantly (P less than 0.005) higher than in group 1 (8 +/- 4%) when measured at 48 h. We conclude that the protection offered by uninephrectomy is not a consequence of hypertrophy but that alterations in the environment which follow ischemia to all functioning excretory renal tissue are responsible for the enhanced recovery seen.
Transepithelial and cell membrane electrical resistances of the rabbit proximal convoluted tubule
Authors: Lapointe J. Y. , Laprade R. , Cardinal J.
Published: December 2017

A technique using double-barreled perfusion pipettes and intracellular microelectrodes was developed to measure transepithelial, apical, and basolateral membrane electrical resistances in isolated rabbit proximal convoluted tubules (PCT). This technique has been tested successfully with respect to cable analysis: the transepithelial resistance (RT) did not change with tubule length and the measured core resistance of the lumen (RC) varied according to prediction with lumen diameter and perfusate resistivity. In control solutions, a linear I-V relationship was observed at the entry of the tubule for current varying from -300 to +300 nA. The mean RT was 1,050 +/- 70 omega X cm (n = 33) (a specific resistance of 8.2 omega X cm2). Bath proteins and large variations in transtubular hydrostatic pressure had no significant effect on RT, whereas RT was not systematically related to transepithelial PD or to the sodium-to-chloride permeability ratio (n = 22). Perfusate substitution of 50 mM NaCl by mannitol increased RT by 21% (n = 7) but the same maneuver in the peritubular solution had no significant effect after a 5-min equilibration period. The ratio of apical to basolateral cell membrane resistance (RA/RBL) determined with intracellular microelectrodes was 3.1 +/- 0.3 (n = 27) in control solutions and increased within 1 min by 36% (n = 8) when glucose and alanine were replaced by mannitol in the perfusate solution. Using simultaneous initial changes in transepithelial and basolateral potential differences when glucose and alanine were removed, the individual values of RA and RBL were determined. Mean RBL was 4,900 +/- 990 omega X cm (39 +/- 1.3 omega X cm2) and mean RA was 15,000 +/- 4,300 omega X cm (118 +/- 33 omega X cm2).
Urea and Na+ permeabilities in toad urinary bladder: one or two solute pathways?
Authors: Hardy M. A.
Published: December 2017

It has been reported that toad urinary bladder amiloride not only reversibly blocks Na+ transport, but it also reversibly inhibits urea permeability (Pu). This finding prompted some queries: 1) Does Na+ transport rates and/or the cytosolic Na+ pool regulate Pu? 2) Does amiloride inhibit two different solute pathways or one pathway through which both Na+ and urea permeate? The following results were obtained in toad bladder. 1) The absence of mucosal Na+ does not interfere with basal or ADH-induced Pu. 2) Amiloride inhibits Pu in the absence of apical Na+. 3) The concentration of amiloride that produces half-maximal inhibition (K1/2) of the ADH-induced Na+ transport is 7 X 10(-7)M with 110 mM mucosal Na+, 7 X 10(-8)M with 1 mM apical Na+, and 2 X 10(-6)M in the absence of mucosal Ca2+; K1/2 of ADH-stimulated Pu is 9 X 10(-5)M and is not altered by lowering the mucosal Na+ concentration to 1 mM or deleting apical Ca2+. 4) Mucosal La3+ (10(-3)M): i) reversibly increases Na+ transport by 75%, potentiating the natriferic effect of ADH by 51%; ii) does not affect basal Pu and irreversibly blunts the ADH-mediated increase in Pu by 72%; and iii) has no effect on basal or ADH-induced osmotic flow. Identical results were obtained with Tm3+. These results suggest that the inhibitory effect of amiloride on amide permeation is not mediated by its effect on Na+ transport. There are three separate operational pathways for water, Na+, and urea; amiloride reversibly blocks those through which Na+ and urea permeate.(ABSTRACT TRUNCATED AT 250 WORDS)