bluuebunny/crossref_metadata_2025 huggingface dataset:
Prostaglandin E2 production by rabbit urinary bladder
Authors: Brown W. W. , Zenser T. V. , Davis B. B.
Published: December 2017

Synthesis of prostaglandin E2 (PGE2) by rabbit bladder was examined. PGE2 synthesis was assessed by thin-layer chromatographic analysis after conversion of [14C]-arachidonic acid to [14C]PGE2 or by a specific radioimmunoassay technique. Intact bladder and microsomes prepared from the bladder transitional epithelium (mucosal) layer and the outer vesicular layer demonstrated synthesis of PGE2. PGE2 synthesis was increased by arachidonic acid and blocked by indomethacin. When the inside medium (bathing the transitional epithelium) contained [14C]arachidonic acid, no detectable radioactivity was observed in the outside medium (bathing the outer layer). Conversely, when the outside medium contained [14C]arachidonic acid, no detectable radioactivity was observed in the inside medium. In addition, [14C]arachidonic acid was incorporated only into tissue directly exposed to bathing media containing the label. These results demonstrate that the rabbit bladder can synthesize PGE2 and that the PGE2- synthesizing systems of the transitional epithelium and outer layer of bladder may be distinct.
Inhibition of short-circuit current in toad urinary bladder by inhibitors of glandular kallikrein
Authors: Orce G. G. , Castillo G. A. , Margolius H. S.
Published: December 2017

Aprotinin, a reversible inhibitor, and D-Phe-Phe-Arg-chloromethyl ketone (DPPA), an irreversible inhibitor of mammalian glandular kallikreins, decreased short-circuit current (SCC) in the isolated toad urinary bladder. Both were more potent and rapidly acting on the mucosal than serosal surface. The maximal inhibition in basal SCC was 29% for aprotinin and 41% for DPPA at concentrations of 7.0 X 10(-6) and 1.0 X 10(-5) M, respectively. SCC inhibition with mucosal aprotinin was reversed by rinsing, whereas inhibition with mucosal DPPA was not reversible. The presence of either agent in the mucosal bath inhibited the SCC increase to serosal vasopressin, but neither modified this response when present in the serosal bath. Neither agent affected basal or vasopressin-stimulated osmotic water permeability. Aprotinin did not prevent aldosterone-induced increases in SCC. Soybean trypsin inhibitor, an inhibitor of plasma but not glandular kallikrein, did not affect SCC. We postulate that these inhibitors of mammalian glandular kallikreins act upon some accessible serine proteinase(s) to reduce short-circuit current. This protein(s) might be an amphibian homologue of mammalian renal kallikrein.
Urate secretion in isolated rabbit renal tubules
Authors: Chonko A. M.
Published: December 2017

The flux of radioactive urate from bath to lumen was measured in isolated proximal convoluted (PCT), proximal straight (PST), and cortical collecting tubules (CCT). Urate was secreted in the PST as evinced by a) accumulation of urate in the lumen of perfused tubules to levels 2–4 times greater than in the bath, and b) inhibition of urate flux (bath to lumen) by cooling, by probenecid (2.5 X 10(-4) M), and by ouabain (10(-4) M). Urate secretion was strongly dependent on the rate of urinary flow, diminishing as flow rate was reduced below 2 nl/min, and reaching maximal rates when flow exceeded 5 nl/min. The isotopic urate (either [2–14C]urate or [6–14C]urate) was secreted without modification. Luminal urate was not impressively elevated above the concentration of the bath in PCT. Cortical collecting tubules were relatively impermeable to urate. It is concluded that urate secretion occurs predominantly in the PST of this species by a mechanism dependent on the uphill transport of the molecule from the bath into the urine.
Identifying secondary active solute transport in epithelia
Authors: Aronson P. S.
Published: December 2017

This Editorial Review analyzes the adequacy of the strategies that are commonly used to establish whether the active transport of a solute does or does not occur by secondary active transport. First, the energetics of noncoupled (passive) diffusion, primary active transport, secondary active transport (coupled diffusion), and solvent drag are briefly described. Second, the kinetics of noncoupled and coupled diffusion processes are discussed. Third, the special difficulties of identifying secondary active solute transport in epithelia are outline. Several factors are described that may obscure or mimic true coupled diffusion. Last, the use of transport inhibitors for identifying coupled diffusion processes is briefly illustrated. The adequacy of the strategies that have been employed to evaluate the role of luminal membrane Na+-H+ exchange in mediating proximal tubular acidification is particularly emphasized. It is concluded that many of the findings apparently supporting a major contribution of Na+-independent, primary active H+ secretion to the proximal tubular acidification process are not necessarily inconsistent with secondary active H+ secretion via Na+-H+ exchange.
Urea secretion in medullary collecting duct of the rat kidney during water and mannitol diuresis
Authors: Wilson D. R. , Sonnenberg H.
Published: December 2017

During steady-state water or mannitol diuresis, the microcatheterization technique was used to study the handling of urea, fluid, sodium, potassium, and total solute along the length of the medullary collecting duct in anesthetized rats. During water diuresis, the remaining fraction of filtered urea increased along the collecting duct as indicated both by regression analysis of all samples and by comparison of paired data from the beginning and end of the duct [(TF/P)urea/In = 43.3 and 50.7%, respectively]. During mannitol diuresis, similar urea entry into the medullary collecting duct was observed, (TF/P)urea/In increasing from 60.7 to 66.5%. Comparison of collecting duct urea handling in proximal and distal segments (beginning to midzone and midzone to papillary tip) suggested that urea entry occurred to a greater extent in the distal portion of the medullary collecting duct. The results demonstrate urea secretion into the medullary collecting duct in diuretic states when urine flow is high and intratubular urea concentration low. Whether urea entry into the collecting duct is an active or passive process cannot be determined from this study, but comparison between urea concentrations in the papillary interstitial fluid and in the urine or tubular fluid raises the possibility of an active urea secretory mechanism in the collecting duct.
Nicotinic acid transport by brush border membrane vesicles from rabbit kidney
Authors: Boumendil-Podevin E. F. , Podevin R. A.
Published: December 2017

The transport of nicotinic acid was investigated in brush border membrane vesicles isolated from rabbit kidney. The imposition of a Na+ gradient (out to in) induced a transient stimulation of nicotinic acid uptake above its final equilibrium value. This stimulation was specific for Na+. The uptake of nicotinic acid by the brush border membranes represented transport into an internal space and occurred in the absence of significant nicotinic acid degradation. The Na+ gradient-dependent uptake of nicotinic acid was saturable, apparent Km = 0.3 mM. Uptake of nicotinic acid was inhibited by its two isomers: picolinic and isonicotinic acid. In contrast, pyridine derivatives with two carboxyl groups or an amide group in addition to the carboxyl group were without inhibitory effect. Evaluation of changes in membrane potential using the lipophilic cation triphenylmethylphosphonium demonstrated that conditions that transiently generated either an interior-positive or an interior-negative membrane potential failed to affect the Na+-dependent transport of nicotinic acid. These findings provide evidence of the existence on the luminal membrane of a Na+ gradient-dependent and electroneutral transport system for nicotinic acid.
Intracellular potentials in rabbit proximal tubules perfused in vitro
Authors: Biagi B. , Kubota T. , Sohtell M. , Giebisch G.
Published: December 2017

Conventional microelectrodes were used to measure the basolateral membrane potential (VBL) in isolated perfused superficial proximal convoluted (sPCT) and superficial proximal straight (sPST) tubules of the rabbit kidney. Stable recordings for periods up to 2 h can be obtained. The mean +/- SE (n = number of cells) values of VBL were sPCT = -51.0 +/- 1.63 (24) and sPST = -47.0 +/- 0.97 (94) mV. Inhibitors of active transport, ouabain (10(-5) M) and low bath potassium (0.1 mM), caused a significant depolarization of VBL in sPST. In contrast, short-duration bath cooling (10 degrees C) had no significant effect. Removal of luminal glucose caused a larger hyperpolarization in sPCT (-13.9 +/- 1.77 (9) mV) than in sPST (-3.8 +/- 1.02 (5) mV). Removal of luminal glucose and alanine resulted in an even larger hyperpolarization of VBL in sPCT (-19.0 +/- 0.44 (6) mV). Perfusion of the lumen with a solution resembling late proximal tubular fluid in sPST resulted in hyperpolarization of VBL (-4.3 +/- 0.85 (4) mV). Reducing bath pH to 6.7 depolarized VBL (39.9 +/- 1.77 (13) mV). This effect can be associated with a decrease in the relative potassium permeability of the basolateral membrane. These results demonstrate the feasibility of using intracellular electrical measurements to determine both luminal and basolateral membrane characteristics in isolated proximal tubular segments.
Relationship between sodium and bicarbonate transport in the rat proximal convoluted tubule
Authors: Chan Y. L. , Giebisch G.
Published: December 2017

The relationship between net sodium and bicarbonate transport was studied by microperfusion of proximal convoluted tubules and peritubular capillaries. Bicarbonate absorption was unchanged as long as the sodium concentration remained above 40 meq/liter, despite reduction of sodium transport to 10% of its control value. At a sodium concentration of 5 meq/liter, fluid absorption was completely abolished but bicarbonate transport was reduced to 39% of its control value. Even at reduction of luminal and peritubular sodium concentrations to nominally zero, bicarbonate transport continued at 23% of its control value. Amiloride, at a sodium concentration of 5 meq/liter, inhibited bicarbonate absorption in a dose-dependent manner. Elevating peritubular pH to 8.4 drastically reduced net bicarbonate transport, whereas fluid absorption was only slightly inhibited. These results are consistent with a dual mechanism of acidification: a sodium-hydrogen exchange that saturates at low extracellular sodium concentrations and an additional sodium-independent mechanism of hydrogen ion secretion.
Carbon dioxide permeability of rabbit proximal convoluted tubules
Authors: Schwartz G. J. , Weinstein A. M. , Steele R. E. , Stephenson J. L. , Burg M. B.
Published: December 2017

CO2 kinetics were studied under conditions in which CO2 partial pressure and either the bicarbonate or hydrogen ion concentrations were unequal in perfusate and bath. A glass pH microelectrode and microcalorimeter were used to measure pH and total CO2 in perfused and collected fluids. Luminal appearance or disappearance of CO2 was determined from the change in concentrations of CO2 and acidic moieties of the buffers between perfused and collected fluids. The pH was not measurably affected by the tubule processes of metabolism, hydrogen ion secretion, and buffer transport because of relatively high flow rates. Since CO2 appearance and disappearance were directly related to CO2 partial pressure differences across the tubule (r = 0.94), this technique provides a valid estimate of transepithelial CO2 flux in response to the driving force of a CO2 partial pressure difference. From flux per unit of driving force and from estimates of resistances to CO2 diffusion in both internal and external unstirred layers, we obtained a transepithelial CO2 permeability of approximately 10(-4) cm3 . s-1 . cm tubule length-1. This corresponds to a diffusion coefficient through the tubule epithelium about half that through an equivalent thickness of water. We conclude that rabbit proximal convoluted tubules are so highly permeable to CO2 that even if all the filtered bicarbonate were reabsorbed by the generation of CO2 in the lumen, the tubular fluid CO2 partial pressure would exceed that of the peritubular blood by less than 4 mmHg.
Evidence for interference of 25(OH)vitamin D3 with phosphaturic action of glucagon
Authors: Popovtzer M. M. , Wald H.
Published: December 2017

The effect of 25(OH)vitamin D3 [25(OH)D3] on the phosphaturic action of glucagon was studied using clearance techniques in the following groups of rats: group 1, parathyroidectomized (PTX) glucagon-infused rats receiving intravenous 25(OH)D3; group 2, PTX 25(OH)D3-pretreated rats receiving intravenous glucagon; and group 3, the thyroparathyroidectomized glucagon-infused rats receiving intravenous 25(OH)D3. The effect of 25(OH)D3 on glucagon-induced increase of cAMP in kidney slices and glucagon-activated adenylate cyclase (AC) in kidney membrane fractions was studied in vitro. In group 1, 25(OH)D3 suppressed the glucagon-induced phosphaturia by reducing fractional excretion of phosphorus (CP/CIn) from 0.175 +/- 0.02 (mean +/- SE) to 0.112 +/- 0.12 (P less than 0.05); this was associated with a reduction of urinary cAMP from 1,830 +/- 230 to 660 +/- 120 pmol/min (P less than 0.01). In group 2, pretreatment with 25(OH)D3 reduced CP/CIn from 0.221 +/- 0.025 to 0.108 +/- 0.012 (P less than 0.005). In group 3, 25(OH)D3 reduced CP/CIn from 0.165 +/- 0.012 to 0.075 +/- 0.011 (P less than 0.005). In vitro, 25(OH)D3 blunted the glucagon-induced activation of the AC/cAMP system by reducing AC from 570 +/- 30 to 325 +/- 28 pmol cAMP.mg protein-1.h-1 (P less than 0.01) and the cAMP level from 11.2 +/- 0.9 to 8.5 +/- 0.7 pmol cAMP/g wet tissue (P less than 0.05). These results show that 25(OH)D3 blunts the phosphaturic action of glucagon and suggest that this response may be mediated through suppression of the AC/cAMP system.
Efflux of radiolabeled polyethylene glycols and albumin from rat brain
Authors: Cserr H. F. , Cooper D. N. , Suri P. K. , Patlak C. S.
Published: December 2017

Experiments were carried out to evaluate the role of convection in the removal of large molecules from brain interstitial fluid. Radiolabeled test compounds were injected into the caudate nucleus of anesthetized rats through a guide cannula implanted 1 wk previously and the concentrations of isotope in brain and cerebrospinal fluid (CSF) determined at various times after injection. Control studies with 22Na indicate that the permeability of the blood-brain barrier is normal in tissue surrounding the intracerebral injection cannula. For 69,000 dalton serum albumin, 4,000 dalton polyethylene glycol, and 900 dalton polyethylene glycol, clearance from brain approximates a single exponential decay with half times of disappearance of 12.2, 12.6, and 14.4 h, respectively. Similarly in efflux rate, despite a fivefold difference in diffusion coefficient, is consistent with convective losses from brain, and the maximal rate of interstitial fluid removal estimated on the basis of these data is 0.11 microliter.g brain-1.min-1. Only 10-20% of total efflux is into bulk CSF withdrawn from the cisterna magna.
Lactate oxidation and sodium reabsorption by dog kidney in vivo
Authors: Dies F. , Valdez J. M. , Vilet R. , Garza R.
Published: December 2017

Lactate uptake (Qlact) and oxidation (QCO2lact), oxygen consumption (QO2) and net tubular Na+ reabsorption (TNa), were estimated in pentobarbital-anesthetized dogs under control conditions and following unilateral intrarenal injection of ouabain or intravenous infusion of acetazolamide, ethacrynic acid, or furosemide. QCO2lact accounted for approximately half of simultaneous Qlact and for about one-third of QO2 in control periods. Ouabain injection resulted in significant decreases in several functions of the injected kidney: TNa, 46%; TNa/FNa, 36%; QO2, 40%; Qlact, 59%; and QCO2lact, 70%. Acetazolamide infusion decreased TNa, 33%; TNa/FNa, 12%; QO2, 10%; and QCO2lact, 38%; but did not change Qlact. Ethacrynic acid diminished TNa, 60%; TNa/FNa, 36%; QO2, 45%; Qlact, 31%; and QCO2lact, 73%. Furosemide lowered TNa, 37%; TNa/FNa, 28%; QO2, 25%; and Qlact, 48%; but did not change QCO2lact, 2%. Results indicate that decarboxylation is a major pathway of renal lactate metabolism, that lactate oxidation is a substantial source of aerobic energy for the kidney, and that QCO2lact is probably functionally related to sodium reabsorption. This relationship appears to be closer for a fraction of TNa associated with ouabain- and ethacrynic acid-sensitive mechanisms.
Lactate transport by Thamnophis proximal tubule: sodium dependence
Authors: Brand P. H. , Stansbury R. S.
Published: December 2017

We examined the effects of experimental conditions on unidirectional lactate fluxes in isolated perfused Thamnophis proximal tubule. Fluxes were determined by adding L(+)-[U-14C]lactate to perfusate or bath as appropriate (lactate concentration = 1 mM). The lumen-to-bath lactate flux (Jlb lact) was not affected by the manipulations required to exchange perfusate or bath or by substitution of phosphate for bicarbonate buffer. During measurement of Jlb lact, lactate was ordinarily added to the perfusate only. However, addition of 1 mM lactate to the bath had no effect on Jlb lact, indicating no role for exchange diffusion in renal lactate absorption. In contrast, substitution of tetramethylammonium (TMA+) or choline for Na+ decreased Jlb lact by about 75%. The bath-to-lumen flux (Jbl lact) was also decreased by TMA+ substitution for Na+, although by only about 25%. From these and previous results we suggest that in Thamnophis proximal tubule, lactate is absorbed by an active Na+-dependent transport process that probably derives its energy from the lumen-to-cell electrochemical gradient for Na+.
Prolactin metabolism in the rat: role of the kidney in degradation of the hormone
Authors: Emmanouel D. S. , Fang V. S. , Katz A. I.
Published: December 2017

The contribution of impaired prolactin (PRL) degradation to the altered dynamics of this hormone in uremia was investigated in rats. Hyperprolactinemia developed after bilateral nephrectomy (BNx) or ligation of both ureters (BUL), whereas PRL levels remained normal in comparably azotemic animals undergoing urine autoinfusion in which glomerular filtration rate (GFR) was maintained. The renal organ clearance of PRL in control rats accounted for two-thirds of its metabolic clearance rate and was consistently less than GFR. Following BUL and BNx the metabolic clearance of PRL decreased predictably also by two-thirds. The importance of the renal parenchyma in the degradation of prolactin was confirmed during perfusion of isolated rat kidneys. Renal PRL handling involves mainly glomerular filtration and tubular reabsorption, although uptake from peritubular blood is also demonstrable under the high plasma flow conditions obtaining during in vitro kidney perfusion. We conclude that the hyperprolactinemia associated with acute uremia in the rat is not the consequence of the uremic state per se, but results from impaired renal degradation of the hormone.
Effect of metabolic acidosis on renal response to parathyroid hormone in phosphorus-deprived rats
Authors: Beck N.
Published: December 2017

Both metabolic acidosis and phosphorus (Pi) deprivation have been shown to alter not only renal Pi metabolism independent of parathyroid hormone (PTH), but also the phosphaturic response to PTH. In the present studies, we examined the interaction between metabolic acidosis and Pi deprivation on renal handling of Pi in an animal model in which metabolic acidosis was superimposed on 3 days of dietary Pi deprivation. The effect of metabolic acidosis was evaluated after acute (for 3 h) and chronic (for 3 days) administration of HCl. In Pi-deprived and thyroparathyroidectomized rats, chronic acidosis increased both plasma Pi and the basal fractional excretion of Pi (FEPi). Furthermore, chronic acidosis partially restored the phosphaturic response to PTH, which was totally absent in nonacidotic Pi-deprived rats. These effects metabolic acidosis were not demonstrable in acutely acidotic animals. Determination of PTH-dependent cAMP generation and cAMP-dependent protein kinase activation revealed that neither of these parameters was altered by chronic metabolic acidosis in vivo. These results show that in Pi-deprived rats chronic metabolic acidosis induced by HCl administration further modifies the renal handling of Pi associated with Pi deprivation. Further, the renal interaction between acidosis and Pi deprivation is at a step (or steps) after cAMP generation and protein kinase activation.
Isolated perfused salamander proximal tubule: methods, electrophysiology, and transport
Authors: Sackin H. , Boulpaep E. L.
Published: December 2017

Techniques are presented for the isolation and perfusion of renal proximal tubules from the neotenic salamander Ambystoma tigrinum. Methods are described for a determination of normal values for fluid transport and electrophysiological parameters. Stable cellular microelectrode recordings are reported that constitute the first intracellular measurements in an isolated perfused tubule preparation. With identical solutions in lumen and bath, fluid reabsorption averaged 0.28 nl.min-1.mm-1, transepithelial potential difference averaged -4.5 mV, transepithelial resistance was 52.1 omega.cm2, and the transepithelial chloride-to-sodium transference number ratio was 3.4. The basolateral cell membrane potential difference averaged -59.6 mV, and the ratio of apical-to-basolateral cell membrane resistance was between 3.9 and 5. Viability of the isolated perfused salamander proximal tubule preparation is demonstrated by a detailed comparison of the present data with results of in vivo micropuncture experiments on both Necturus and intact Ambystoma kidneys. In addition to being an advantageous preparation for long-term intracellular recordings, the Ambystoma kidney is unique in that proximal tubules can be studied both in isolation and by conventional micropuncture.
Sympathetic system in potassium homeostasis
Authors: Silva P. , Spokes K.
Published: December 2017

The extrarenal disposal of potassium was studied in nephrectomized and adrenalectomized rats by measuring the rise in serum potassium produced during an infusion of 3 meq KCl/kg over 90 min. Adrenalectomy alone did not alter the volume of distribution of infused potassium in nephrectomized animals. When nephrectomy and adrenalectomy were combined with either insulin deficiency produced by streptozotocin or chemical sympathectomy induced by injection of 6-hydroxydopamine, potassium tolerance was significantly impaired. Hyperkalemia produced in chemically sympathectomized animals by potassium infusion was minimized by simultaneous infusion of epinephrine, an effect blocked by the beta-antagonist propranolol but not by the alpha-blocker phenoxybenzamine. These results suggest that extra renal uptake of potassium, in addition to being influenced by insulin and circulating catecholamines, is modulated by peripheral sympathetic activity.
Hormonal induction of Na-K-ATPase in developing proximal tubular cells
Authors: Aperia A. , Larsson L. , Zetterstrom R.
Published: December 2017

The outer 150-micrometers layer of the renal cortex of the rat consists mainly of proximal tubules (PT). In this layer Na-K-ATPase (mumol Pi . mg protein-1 . h-1) increases from 3.45 +/- 0.19 (SE) in 10-day-old rats (R10) to 5.90 +/- 0.28 in 20-day-old rats (R20) to 9.52 +/- 0.42 in 40-day-old rats (R40). Betamethasone in pharmacologic doses increases Na-K-ATPase in R10, R20, and R40 to 11.5 +/- 1.19, 13.4 +/- 0.64, and 13.3 +/- 0.60, respectively. Estrogen in pharmacologic doses increases Na-K-ATPase to 9.1 +/- 0.46 in R20 and decreases Na-K-ATPase to 7.6 +/- 0.39 in R40. Aldosterone in a dose of 10 micrograms/100 g BW increases Na-K-ATPase to 8.7 +/- 0.26 in R20; in a dose of 40 micrograms/100 g BW it increases Na-K-ATPase to 6.9 +/- 0.35 in R10. However, aldosterone in a dose of 80 micrograms/100 g BW is needed to cause an increase in R40 to 13.4 +/- 0.37. Treatment with canrenone from the 10th to the 20th day increases Na-K-ATPase. It is concluded that the immature PT cells are particularly sensitive to hormone induction of Na-K-ATPase and that the sensitivity is maximal during fairly late stages of cellular differentiation. Moreover, the inductive effect is probably mediated via glucocorticoid receptors.
Potassium secretion by cortical collecting tubule: relation to sodium absorption, luminal sodium concentration, and transepithelial voltage
Authors: Stokes J. B.
Published: December 2017

Sodium absorption and K secretion were measured in isolated perfused rabbit cortical collecting tubules. To increase the range of transport rates some tubules were dissected from rabbit pretreated with DOcA. K secretin was unaffected by varying axial volume flow from 4 to 15 nl/min. K secretion was, however, correlated with transepithelial voltage and Na absorption. The Na:K transfer ratio was 1.35. In tubules dissected from normal rabbits, K secretion was almost eliminated by reducing Na concentration in the lumen to near 0 and was unaffected by varying luminal Na concentration from 30 to 145 mM. These data, together with other experimental results reported by several investigators, are consistent with a model for K secretion that places the rate-limiting step at the Na-K pump located on the basolateral membrane. The apical (luminal) membrane appears to be highly permeable to K.
NaCl transport in mouse medullary thick ascending limbs. III. Modulation of the ADH effect by peritubular osmolality
Authors: Hebert S. C. , Culpepper R. M. , Andreoli T. E.
Published: December 2017

We evaluated the effects of increasing bath osmolality on both the passive permeability properties and the ADH-dependent rates of net Cl- absorption in isolated mouse medullary thick ascending limbs of Henle (mTALH). Increases in both osmolality to 900 mosmol/kg H2O with 600 mM urea had no effect on either the electrical (PNa/PCl ratio, 1.7 and 1.9 with and without peritubular urea, respectively) or tracer (PNa, 0.21 and 0.22 micrometers . s-1 with and without peritubular urea, respectively) ionic permeability characteristics of the mTALH. However, this degree of urea bath hypertonicity reduced reversibly both JnetNaCl, the net rate of transepithelial NaCl absorption, and Ve, the spontaneous transepithelial voltage: JnetNaCl fell by 85% and Ve by 70%. Both of these latter effects could be accounted for quantitatively by an 85% reduction in tau NaCl, the rate of conservative transcellular NaCl transport. The inhibition of Ve by peritubular medium urea hypertonicity was not altered by supramaximal bath concentrations of ADH, supramaximal bath concentrations of cAMP analogues, or symmetrical addition of urea to perfusate and bath. Increases in peritubular medium mannitol concentrations also reduced Ve; the inhibition of Ve was not reversed by supramaximal bath concentrations of aDH. Cell volume remained unchanged with peritubular urea but was reduced by peritubular mannitol. These data indicate that in the mTALH increases in bath osmolality with nonelectrolytes inhibit tau NaCl noncompetitively with respect to ADH or cAMP and independently of cell volume. JnetCl was also reduced with increases in peritubular medium NaCl concentration and was associated with a reduction in cell volume.
Increased fluid absorption and cell volume in isolated rabbit proximal straight tubules after in vivo DOCA administration
Authors: Knepper M. A. , Burg M. B.
Published: December 2017

To investigate whether mineralocorticoids affect the intrinsic capacity of the proximal tubule to absorb sodium and fluid, rabbits were chronically treated a number of ways to systematically vary plasma concentrations of mineralocorticoid hormones. The rate of fluid absorption and tubule dimensions were measured in superficial S2 segments from these rabbits. Chronic administration of deoxycorticosterone acetate (DOCA) was associated with a 67% increase in fluid absorption and a 29% increase in cell volume per unit tubule length. However, neither adrenalectomy nor low sodium diet significantly affected either fluid absorption or cell volume. Furthermore, marked dietary sodium restriction prevented the response to DOCA. We conclude that the DOCA-induced increases in fluid absorption and cell volume do not result from a direct stimulation of the proximal tubular cells by the steroid but more likely are responses to systemic effects of DOCA administration that are dependent on the level of sodium intake. Thus, we find no evidence for a direct mineralocorticoid stimulation of sodium and fluid transport by the S2 portion of the proximal tubule.
Renal tubular handling of zinc in the dog
Authors: Victery W. , Smith J. M. , Vander A. J.
Published: December 2017

Clearance and stop-flow techniques, performed on anesthetized dogs, were used to obtain evidence for renal tubular reabsorption or secretion of 65Zn (administered intravenously with varying amounts of carrier ZnCl2). Ultrafilterability of plasma 65Zn was determined in vitro with Amicon CF-50A filter cones. Clearances were obtained under six conditions: antidiuresis, mannitol diuresis alone and following the infusion of chlorothiazide, citrate, cysteine, histidine. The percentage of ultrafilterability averaged, respectively, 1.15, 1.38, 0.91, 1.53, 19.90, and 11.61, while fractional zinc excretion averaged 0.046, 0.10, 0.31, 0.43, 0.78, and 0.12, respectively. Control stop-flow patterns invariably showed net Zn reabsorption in the distal nephron. Stop-flow patterns after chlorothiazide revealed significant net secretion in the far distal area in all animals. Patterns after either citrate or histidine infusion revealed significant net reabsorption in the proximal nephron. Those after cysteine were similar to the control patterns. Thus, both clearance and stop-flow experiments revealed net reabsorption as the major tubular mechanism of zinc handling, tubular secretion occurring only during chlorothiazide administration.
Prior mannitol and furosemide infusion in a model of ischemic acute renal failure
Authors: Hanley M. J. , Davidson K.
Published: December 2017

Tubular transport abnormalities have recently been characterized in a rabbit model of ischemic acute renal failure (ARF). These studies demonstrated severe observable morphologic and functional changes in the proximal nephron together with functional changes in the distal nephron. Tubular debris was often produced by perfusion of proximal nephron segments. In the present study, agents used to prevent ARF were tested in this rabbit model of ARF. Rabbits were infused with either 5% body wt 5% manitol or 20 micrograms . kg-1 . min-1 furosemide in 5% body wt normal saline for the 60 min preceding 60 min of total renal ischemia. Mannitol 1) prevented the development of ARF, 2) maintained fluid reabsorption in the proximal convoluted tubule (PCT) (0.59 +/- 0.03 vs. 0.52 +/- 0.1 nl . mm-1 . min-1) and proximal straight tubule (PST) (0.34 +/- 0.05 vs. 0.39 +/- 0.07 nl . mm-1 . min-1), 3) depressed NaCl reabsorption in the cortical thick ascending limb of Henle's loop (TALH), and 4) did not prevent a decrease in ADH-mediated osmotic water flow in the cortical collecting tubule (CCT). Furosemide 1) partially preserved renal function, 2) partially protected the PCT (0.63 +/- 0.05 vs. 0.38 +/- 0.04 nl . mm-1 . min-1) and PST (0.32 +/- 0.04 vs. 0.22 +/- 0.02 nl . mm-1 . min-1), and 3) did not change the transport capacity of the TALH or the ADH response of the CCT. Preservation of proximal nephron integrity was also reflected by the absence of debris formation. There is a direct relation between an agent's ability to protect the functional integrity of the cells of the proximal nephron and its ability to preserve renal function.
Acute metabolic acidosis augments collecting duct acidification rate in the rat
Authors: Graber M. L. , Bengele H. H. , Mroz E. , Lechene C. , Alexander E. A.
Published: December 2017

It is generally assumed that at least part of distal acidification occurs along the collecting duct. Complete and direct evaluation of acidification along this nephron segment is unavailable, however. The purpose of these experiments was to quantify the net acidification rate along the inner medullary collecting duct (IMCD) and to measure the effect of acute HCl acidosis. In 13 control rats (arterial pH, 7.39 +/- 0.01; PCO2, 39 +/- 1 mmHg) and 11 HCl-infused rats (arterial pH 7.18 +/- 0.01; PCO2, 40 +/- 1 mmHg) we obtained four to eight IMCD samples by a modified microcatheterization technique that also permitted measurement of in situ and in vitro pH. Tubular fluid pH decreased along the IMCD in both groups and was more acidic by 0.2–0.4 pH units in the acid-infused rats. Bicarbonate reabsorption was noted in both groups as delivery along the IMCD decreased from 205 +/- 127 to 26 +/- 6 nmol/min in control rats and from 219 +/- 118 to 17 +/- 4 nmol/min in the acidotic group. Ammonia delivery to and addition along the IMCD was significantly greater in the acidotic rats--from 193 +/-- 59 to 462 +/- 53 nmol/min in control and from 887 +/- 126 to 1,396 +/- 90 nmol/min in acidotic rats. No significant change in total or titrated phosphate was seen. Net acid addition along the IMCD was over twice as great in acidotic rats, 450 vs. 970 nmol/min. Our results indicate that significant net acid addition occurs along the IMCD and that during acidosis this acidification rate increases.
Intracellular potassium activity in the rabbit proximal straight tubule
Authors: Biagi B. , Sohtell M. , Giebisch G.
Published: December 2017

Double-barreled liquid ion-exchanger microelectrodes were used to measure basolateral membrane potential (VBL) and intracellular potassium activity (aiK) in superficial proximal straight tubules (sPST) of the rabbit perfused in vitro. The mean +/- SE (number of cells in parentheses) value of VBL was -37.8 +/- 2.49 (20) vM and aiK was 48.6 +/- 2.27 (20) mM. The calculated Nernst equilibrium potential (EK) across the basolateral membrane was -68 mV. Lowering both potassium concentration to 0.1 mM reversibly decreased both VBL and aiK to -12.2 +/- 1.21 (19) mV and 11.3 +/- 1.29 (19) mM, respectively. Bath ouabain (10(-5) resulted in similar changes. These results demonstrate that intracellular potassium is actively accumulated in sPST perfused in vitro and that accumulation results primarily from Na-K-ATPase activity in the basolateral membrane. During recovery from low K bath, the temporal relationship between VBL and aiK and the effects of ouabain and high K bath on recovery are used to demonstrate directly electrogenic pumping. Lowering bath pH to 6.7 (HCO-3 = 5 mM) and the presence of 0.5 mM BaCl2 in the bath resulted in a large and rapid depolarization of VBL with little or no change in aiK. These results suggest that the response of VBL to both maneuvers is caused by a decrease in potassium permeability of the basolateral membrane.
From toad bladder to kidney
Authors: Leaf A.
Published: December 2017

Studies using the urinary bladder of the toad to elucidate the mechanism of transepithelial ion transport are reviewed. Sodium ions are reabsorbed from bladder urine across the granular cells, accounting for all the electrical activity of this epithelium. Sodium ions enter the granular cells passively through selective sodium channels down an electrochemical gradient, mix in the intracellular "active transport pool," and are pumped actively out of the cell across the basolateral plasma membrane. The concentration of sodium within the active transport pool is normally low, 10-14 mM, with Ringer solution bathing both surfaces. The apical plasma membrane is the major resistance barrier; both vasopressin and aldosterone stimulate sodium transport across the tissue by increasing the permeability of this barrier. The apical plasma membrane is impermeable to chloride ions and they are reabsorbed passively, in response to the transepithelial electrical potential established by active sodium transport, through paracellular channels. The bladder reabsorbs 18 sodium ions per molecule of suprabasal oxygen consumed. The relatively high apical membrane resistance buffers the basolateral active transport system from changes in osmotic work in pumping sodium out of the cell over the physiologic range of transepithelial potentials.
Glucose and alanine inhibition of phosphate transport in renal microvillus membrane vesicles
Authors: Barrett P. Q. , Aronson P. S.
Published: December 2017

Transport interactions among phosphate, glucose, and alanine were evaluated in brush border membrane vesicles isolated from the rabbit renal cortex. Both glucose and alanine inhibited the Na+ gradient-stimulated uphill accumulation of phosphate. Neither glucose nor alanine inhibited the phosphate uptake measured in the absence of Na+ or in the presence of a collapsed Na+ gradient shunted with amphotericin B. Phosphate and alanine inhibited the Na+ gradient-stimulated uphill accumulation of glucose but not the glucose uptake measured in the presence of a collapsed Na+ gradient shunted with amphotericin B. Alanine, which was more potent than glucose or phosphate in inhibiting Na+ gradient-stimulated solute transport, was also more potent than glucose or phosphate in stimulating the uptake of Na+ into the vesicles. We conclude that the inhibitory interactions among phosphate, glucose, and alanine probably represent indirect effects resulting from solute-induced alterations in the transmembrane electrochemical Na+ gradient rather than direct effects resulting from competition for a polyfunctional carrier or from allosteric interactions. Such a mechanism could explain the inhibitory interactions among phosphate, glucose, and alanine that have been observed in the intact proximal tubule.
High-affinity Ca-Mg-ATPase along the rabbit nephron
Authors: Doucet A. , Katz A. I.
Published: December 2017

Maintenance of cell calcium homeostasis and transepithelial transport of this cation require its extrusion from the cell against a steep electrochemical gradient. Because it has been proposed that a membrane Ca-ATPase activated by micromolar concentrations of Ca2+ prevailing in the cell participates in these processes, we attempted in this study to determine whether such an enzyme is present in the rabbit nephron. A magnesium-dependent ATPase, maximally activated by Ca2+ (Ca-Mg-ATPase) concentrations between 1.1 and 2.3 microM (apparent Km = 0.3-0.4 microM), was found in all segments of the nephron. Ca-Mg-ATPase (pmol.mm-1.h-1) was highest in the distal convoluted tubule (243) and cortical collecting tubule (208), intermediate in the proximal convoluted tubule (140) and medullary thick ascending limb of Henle's loop (135), and lower in the pars recta (97), cortical thick ascending limb (50), and medullary collecting tubule (51). The enzyme was insensitive to ouabain and vanadate, but was inhibited by ruthenium red in a dose-dependent manner (Ki congruent to 2.10(-6) M). Sodium azide, an inhibitor of mitochondrial ATPase, did not affect Ca-Mg-ATPase, suggesting that the enzyme was located in the plasma membrane. The Ca-Mg-ATPase activity measured in most segments of the rabbit nephron in this study appears sufficient to account in theory for the active component of the unidirectional (lumen-to-bath) calcium flux found in the corresponding region of the nephron with in vitro single tubule microperfusion techniques.
Effects of pH on potassium transport by renal distal tubule
Authors: Stanton B. A. , Giebisch G.
Published: December 2017

To determine the relative importance of plasma and luminal pH changes as factors regulating potassium secretion by rat distal tubule, superficial tubules were continuously microperfused in vivo. The effects of changes in plasma pH were examined by producing acute systemic metabolic acidosis or alkalosis and holding luminal flow rate, solute composition, and pH constant by microperfusion. Alternatively, the effect of luminal solution pH was evaluated by microperfusing tubules with solutions buffered to either pH 6.5 or 8.0 at constant systemic acid-base balance. Net transport of Na and K and the pH of the luminal fluid were measured. Results showed that metabolic acidosis inhibited and metabolic alkalosis stimulated potassium secretion. Increased luminal fluid pH, in contrast, did not stimulate potassium transport. In experiments in which metabolic acidosis produced a diuresis, urinary potassium excretion was enhanced compared with hydropenic controls. Free-flow micropuncture studies revealed that the rate of fluid delivery to the distal tubule was 45% greater during acidosis compared with control and that potassium secretion increased in both the distal and collecting tubule. Since the rate of fluid delivery is a potent stimulus of potassium secretion in the distal tubule, it is concluded that the stimulus of increased delivery of fluid, observed in free-flow conditions, masked the inhibitory effect of acidosis on potassium transport. Potassium transport by the distal tubule, during acid-base disorders, is regulated by plasma pH and the rate of delivery of fluid but is not stimulated by alkalinization of the luminal fluid.
Specialized function of carbonic anhydrase-rich and granular cells of turtle bladder
Authors: Schwartz J. H. , Bethencourt D. , Rosen S.
Published: December 2017

The mucosal surface of the turtle bladder consists of two major cell types, carbonic anhydrase-rich (CA) and granular (G) cells. These cells types may have specific transport functions. To separate and study these cells, they were removed from the bladder by collagenase digestion and then separated into two distant subpopulations by Ficoll discontinuous density-gradient centrifugation. By morphological criteria the lighter subpopulation (band II) consists primarily of CA cells and the denser population (band III) G cells. The distribution of two enzymes important for H+ transport, CA and glucose-6-phosphate dehydrogenase (G-6-PD), and the effect of specific transport inhibitors, acetazolamide and ouabain, on O2 consumption of these cells was examined. The CA activity of band II cells was 4.5 times greater than that of band III cells. The G-6-PD activity of band II cells was 2.2 times greater than that of band III cells. The rate of O2 consumption of band II cells, 4.73 microliters.mg protein-1.h-1, was reduced 40% by 5 X 10(-5) M acetazolamide but not by ouabain. Band III O2 consumption, 3.43 microliters.mg protein-1.h-1, was reduced 30% by 10(-4) M ouabain but not by acetazolamide. On the basis of the distribution of CA and G-6-PD and the effect of acetazolamide and ouabain on O2 consumption, we propose that CA cells are primarily responsible for H+ transport and G cells for Na+ transport.
Dopamine decreases fluid reabsorption in straight portions of rabbit proximal tubule
Authors: Bello-Reuss E. , Higashi Y. , Kaneda Y.
Published: December 2017

The effects of DA and DA blockers on fluid transport, transepithelial potential difference (PD), and Na fluxes were studied in straight portions of the rabbit proximal tubule by the technique of microperfusion in vitro. DA (10(-6) M) added to the bath (rabbit serum) produced a significant decrease in fluid reabsorption (Jv, nl.min-2.mm-1) from 0.53 +/- 0.05 to 0.19 +/- 0.06 (n = 7, P less than 0.005). PD decreased from -2.7 +/- 0.5 to -1.2 +/- 0.4 mV (P less than 0.01). Drugs active on DA receptors were used to characterize the action of dopamine. Haloperidol (10(-8) M), lisuride (1.5 X 10(-9) M), and metoclopramide (10(-7) M) did not modify Jv by themselves but prevented the action of dopamine. Agonists of DA, Epinine and A 6,7 DTN, produced smaller or shorter decreases in Jv. A 6,7 DTN was active in the presence of alpha- and beta-adrenergic blockers. The serotonin antagonist methysergide decreases Jv by itself by 15%; in its presence DA was not effective. The effect of DA was accompanied by reductions of net Na flux and unidirectional lumen-to-bath and bath-to-lumen Na fluxes by approximately 25%. It is concluded that DA exerts a direct inhibitory effect on fluid transport by the pars recta. The evidence for the existence of DA receptor sites is not conclusive. The mechanism of action is uncertain, but an impairment of transcellular salt transport can be suggested.
Water reabsorption by papillary collecting ducts in the remnant kidney
Authors: Pennell J. P. , Bourgoignie J. J.
Published: December 2017

Water transport by terminal papillary collecting ducts was examined by micropuncture of the renal papilla in 15 rats with a solitary remnant kidney (RK) and in 27 normal rats, 10 of which had undergone sham operation. Before papillary exposure, urinary osmolality was significantly (P less than 0.001) lower in RK rats (685 vs. 1,722 mosmol/kg H2O in normal rats). After papillary exposure, urinary osmolality decreased by 50% in normal rats but did not change in RK rats. In RK rats, a greater percentage of filtered water was delivered to (5.74% vs. 2.29% in normal rats, P less than 0.001) and reabsorbed by (1.94% vs. 0.94% in normal rats, P less than 0.005) the terminal millimeter of papillary collecting ducts. Fractional water reabsorption by terminal papillary collecting ducts correlated directly (r = 0.83, P less than 0.001) with fractional water delivery, suggesting load dependence of water reabsorption. Estimated absolute water reabsorption by terminal collecting ducts was equivalent for remnant and normal kidneys and increased two-to fourfold in remnant kidneys when analyzed per functioning papillary collecting duct. There was an inverse relationship between urinary osmolality and fractional water delivery to papillary collecting ducts (r = 0.65, P less than 0.001). Although the data do not exclude functional alterations of papillary collecting ducts, the events underlying the reduction of urinary osmolality in remnant kidneys appear to involve physiological processes based on a high delivery and reabsorption of water.
Cimetidine and procainamide secretion by proximal tubules in vitro
Authors: McKinney T. D. , Speeg K. V.
Published: December 2017

Previous studies have shown that organic bases, including some drugs, are secreted by renal proximal tubules. The present studies examined the transport of the organic bases cimetidine and procainamide by rabbit proximal straight tubules perfused in vitro. Both drugs were secreted into the tubule lumen. [3H]cimetidine secretion was reduced by quinidine, procainamide, and N-acetylprocainamide. Previous studies showed that cimetidine secretion was reduced by other organic bases. Hypothermia and ouabain inhibited [3H]procainamide secretion as was shown previously for cimetidine secretion. [3H]procainamide secretion was also reduced by quinidine, cimetidine, procainamide, and N-acetylprocainamide but not by probenecid. High concentrations of cimetidine (10(-3) M) had no effect on the rates of fluid or total CO2 absorption. When analyzed in terms of Michaelis-Menten kinetics, the effect of cimetidine on procainamide secretion and procainamide on cimetidine secretion was consistent with competitive inhibition. The results suggest that both cimetidine and procainamide are secreted into the lumen of proximal straight tubules predominately by an organic base transport mechanism. These studies raise the possibility that some of these drugs might compete for a common secretory mechanism in renal tubules and reduce the elimination of each other.