bluuebunny/crossref_metadata_2025 huggingface dataset:
On equations for combined convective and diffusive transport of neutral solute across porous membranes
Authors: Bresler E. H. , Groome L. J.
Published: December 2017

The process of combined convection and diffusion of solute across membranes of finite thickness is discussed. An exact solution is available for an open (nonsieving) homoporous membrane. This solution is nonlinear in the volume flux (Jv) for any nonzero volume flow and concentration difference. Extension to the more general case of a partially sieving membrane does not change the nonlinear form of this equation. A linearization of this transport equation about small Jv/Ps yields an approximate equation (the arithmetic mean) that is useful over a reasonable range of conditions near equilibrium. The application of linear nonequilibrium thermodynamics to this process has led to the derivation of a third transport equation, linear in Jv but logarithmic in the concentrations. This finite difference equation is shown to give a less accurate approximation to the exact equation than does the arithmetic mean equation, even in regions near equilibrium. Use of approximate equations may lead to error when the solute reflection coefficient is determined from ultrafiltration experiments or when applied to the individual elements of a membrane array. The early origins of the concept of reflection and sieving coefficients and their relation to one another are discussed. The importance of structural detail in membranes, even at a fine-grained level, and the distinction between the terms "homogeneous" or "black box" and "homoporous" is emphasized. Although structural complexity creates problems in any attempt to write a transport equation without detailed knowledge of the membrane stucture, proper consideration of the local equation and its subsequent integration makes this fact explicit and allows for an assessment of the magnitude of these effects.
pH and PCO2 profiles of the rat inner medullary collecting duct
Authors: Graber M. L. , Bengele H. H. , Schwartz J. H. , Alexander E. A.
Published: December 2017

To directly characterize acidification by the collecting duct, we developed pH and PCO2 microelectrodes suitable for microcatheterization of the inner medullary collecting duct (IMCD). In saline-infused control rats apparent in situ pH fell significantly along the IMCD, from 5.95 at 60% length to 5.49 at the papilla tip. Luminal PCO2 averaged 34 +/- 1 mmHg and PD averaged +3 mV. In rats acutely infused with 0.1 N HCl, apparent in situ pH also decreased significantly from 5.56 to 5.28, PD averaged +2 mV, and luminal PCO2 31 +/- 1 mmHg. The luminal PCO2 of HCl-infused rats was significantly less than controls and both levels were significantly below arterial PCO2. Corroborating the in situ pH profiles, equilibrium pH measured on collected IMCD samples also decreased significantly with percent length. In samples measured in situ and at equilibrium, a small but significant acid disequilibrium pH ws seen in both groups. We interpret these results to indicate that the IMCD actively participates in distal acidification. It is proposed that acidification by the IMCD is predominantly mediated by hydrogen ion secretion which simultaneously acidifies luminal fluid and generates a cellular sink for CO2, thereby inducing an acid disequilibrium pH by two mechanisms.
Disappearance of calcium and other electrolytes from microvolume samples
Authors: Muhlert M. , Julita M. , Quamme G.
Published: December 2017

Studies involving micropuncture and microperfusion of single nephrons require the handling of very small fluid samples. To facilitate handling, the tubule fluids are normally manipulated under paraffin oil. Calcium and, to a lesser extent, magnesium and phosphate concentrations may change significantly when placed in hydrated paraffin oil. Fluids of alkaline pH (about 7.4), either intrinsic or because of loss of CO2, may very quickly lose calcium in paraffin oil. Evidence suggests that this is due to a reversible binding of calcium and perhaps magnesium to the aqueous-oil interface that is dependent on the pH of the sample. It is recommended that tubule fluid samples be kept acidic to prevent calcium loss. A convenient method is by equilibrating the paraffin oil, prior to placement of aqueous samples, with a CO2 tension sufficient to lower the sample pH to below 7.0.
Substrate-selective maintenance of tissue K+ in perfused rat kidney
Authors: Cohen J. J. , Black A. J.
Published: December 2017

We sought to determine in the functioning, substrate-limited, isolated perfused rat kidney whether there is substrate selectivity for maintenance of renal tissue K+ content (mueq/g dry wt). The kidney was perfused for 75 min with 6 g/100 ml substrate-free albumin in Krebs-Ringer bicarbonate (pH approximately 7.4) in the absence of exogenous substrate (control) or in the presence of one substrate (usually 5 mM) chosen from three groups of substrates: 1) substrates of the glycolytic pathway: glucose, fructose, and glycerol; 2) precursors of or substrates of the tricarboxylic acid cycle: citrate (2 mM), alpha-ketoglutarate, succinate, glutamine, glutamate, and acetate; 3) substrates selectively used by the kidney for synthetic work: glycine and inositol. A significant loss of tissue K+ occurred during perfusion in the absence of exogenous substrate (-17%) and also during perfusion with inositol, glycine, acetate, glutamine, or glycerol. No loss of tissue K+ occurred in the presence of fructose, citrate, alpha-ketoglutarate, succinate, or glutamate. Glucose was unique in that at 10 mM, but not at 5 mM, a loss of tissue K+ occurred. We conclude that there is substrate-selective support of renal tissue K+ content, and that those substrates known to enter principally into energy-requiring biosynthetic pathways do not maintain tissue K+ content.
Renal cortex ion composition and Na-K-ATPase activity in gentamicin nephrotoxicity
Authors: Cronin R. E. , Nix K. L. , Ferguson E. R. , Southern P. M. , Henrich W. L.
Published: December 2017

Abnormalities of potassium and magnesium homeostasis have been reported following the use of gentamicin, and potassium depletion enhances gentamicin nephrotoxicity. The present study investigates these relationships in the dog by assessing changes in renal cortex ion composition and renal cortex Na-K-ATPase activity occurring during gentamicin nephrotoxicity. Gentamicin (15 mg/kg i.m. twice daily) was administered for 4 to 7 days to potassium-depleted or potassium-supplemented animals. The results show that gentamicin nephrotoxicity was characterized by a significant reduction in renal cortex content of potassium (17%), magnesium (19%), and phosphorus (12%) in all groups of animals given gentamicin. However, only potassium-depleted animals exposed to 7 days of gentamicin experienced a significant rise in plasma creatinine (from 1.3 +/- 0.1 to 4.3 +/- 1.0 mg/dl). Accompanying this increase in plasma creatinine was a significant rise in the renal cortex content of sodium (from 25 +/- 0.5 to 27.9 +/- 1.7 meq/100 g fat-free dry solid wt) and calcium (from 1.2 +/- 0.1 to 2.6 +/- 0.3 mM/100 g fat-free dry solid wt). Na-K-ATPase activity in the renal cortex fell only in potassium-depleted animals after 4 days (from 11.5 +/- 0.9 to 7.8 +/- 0.1 microM Pi.mg protein-1.h-1) and 7 days (5.9 +/- 0.8 microM Pi.mg protein-1.h-1) of gentamicin treatment. Thus, gentamicin nephrotoxicity is characterized by sequential changes in renal cortex ionic composition, sodium pump activity, and renal function.
Effects of lysine on bicarbonate and fluid absorption in the rat proximal tubule
Authors: Chan Y. L. , Kurtzman N. A.
Published: December 2017

The effects of lysine on bicarbonate and fluid reabsorption in the rat proximal tubule were studied by luminal and capillary perfusion in situ. The proximal tubule and peritubular capillaries were perfused with bicarbonate Ringer solution containing [14C]inulin. The rate of bicarbonate reabsorption (JHCO3) was estimated to be 124 +/- 9.5 peq.min-1.mm-1 using a pH membrane glass electrode. The rate of net fluid reabsorption (Jv) was 2.6 +/- 0.21 nl.min-1.mm-1. When 10 mM L-lysine was added to the luminal perfusate, a 35% reduction in JHCO3 and no change in Jv were observed. Increase of L-lysine concentration in the luminal perfusate to 20 mM did not reduce JHCO3 further nor did it influence Jv.l When 10 mM L-lysine was added to the capillary perfusate, a 13% reduction in JHCO3 was observed (NS). Increase of lysine concentration in the capillary perfusate to 20 mM significantly reduced JHCO3 by 26% (P less than 0.01). There was no significant change in Jv under both conditions. The effect of L-lysine in the lumen was related to its reabsorption kinetics, D-Lysine, which was not reabsorbed significantly, did not affect bicarbonate reabsorption in the proximal tubule. These results indicate that the inhibitory effect of L-lysine is related to the entry of lysine into the cell from the lumen.
Permeability and channel structure of reptilian skin
Authors: Stokes G. D. , Dunson W. A.
Published: December 2017

A study of the permeability of shed epidermis from some terrestrial and freshwater snakes was conducted. Permeability to Br, Na, and K ions was very low and showed a higher influx than efflux in most cases. Permeability to the smaller water molecule was much greater, and in contrast efflux was higher than influx. Skins from aquatic snakes with larger water permeabilities also showed greater permeabilities to Na and K. The highly aquatic Regina septemvittata has the most permeable skin of any snake. Ethanol fluxes were higher than expected for a tracer of its size, perhaps due to its solubility in lipid. Na fluxes through whole live skins of Nerodia cyclopion floridana in vitro were not significantly different from those of the shed skin alone. Isolated hinge regions showed complete water impermeability, suggesting that channels through the skin are located only in the scale region. Dermal water efflux into dry air was considerably less than water-to-water efflux. Lipid extraction increased permeability markedly and eliminated the asymmetry of water and ion fluxes. Lipid replacement with linoleic acid restored half of the water impermeability lost during extraction. Protein extraction did not significantly increase membrane permeability but did eliminate the permeability difference between dry and hydrated skins. Two sizes of lipid-lined channels extending through a protein matrix are suggested as a possible model for snake skin. The diameter of the channels apparently varies in relation to the differing water, Na, and Cl concentrations on opposite sides of the skin, but the mechanism of this adjustment is unknown.
Na+/H+ antiporter of brush border vesicles: studies with acridine orange uptake
Authors: Warnock D. G. , Reenstra W. W. , Yee V. J.
Published: December 2017

Fluorescence quenching of acridine orange was used to characterize the generation and collapse of pH gradients by the Na+/H+ antiporter of brush border membrane vesicles prepared from rabbit renal cortex. Quenching was observed when acridine orange, a weak base, was taken up to an acidic intravesicular space. Na+/H+ exchange was examined with both Na+ uptake and efflux studies. Acridine orange fluorescence quenching demonstrated the cation specificity of the Na+/H+ antiporter (i.e., sodium and lithium) and was inhibited by amiloride. Parallel studies with nigericin, a K+/H+ antiporter, demonstrated that acridine orange responded very rapidly to pH gradients. Therefore, acridine orange equilibration was not rate limiting in our studies of the Na+/H+ antiporter. Initial rate measurements were made to obtain kinetic parameters for the Na+/H+ antiporter. In sodium influx studies, the half-maximal rate of acridine orange fluorescence change was obtained with an external sodium concentration of 13.3 +/- 0.5 mM.
Role of vasopressin in fetal homeostasis
Authors: Daniel S. S. , Stark R. I. , Husain M. K. , Baxi L. V. , James L. S.
Published: December 2017

The role of vasopressin (VP) and the kidney in the maintenance of solute and volume homeostasis was studied in chronically instrumented fetal lambs during the third trimester. Plasma VP, urine and plasma osmolality, and urine output were measured in 74 simultaneous samples. The results show a strong positive nonlinear correlation between plasma VP and osmolality when a latter is higher than 290 mosmol/kg (r = 0.803, P = 0.03) and between plasma VP and urine osmolality (r = 0.806, P = 0.05). No correlation was found between fetal and maternal plasma VP. However, linear correlations were found in plasma osmolality and sodium concentrations between mother and fetus; mean maternal-fetal gradients were 4 mosmol/kg and 3.1 meq/liter, respectively. The highest values for plasma VP and osmolality found in our study were 7.0 pg/ml and 317 mosmol/kg, respectively. There values corresponded to urine output of 0.02 ml.kg-1.min-1 and osmolality of 517 mosmol/kg. In conclusion, there studies demonstrate that the relationship among plasma osmolality, plasma vasopressin concentration, and urine osmolality in the lamb fetus are qualitatively similar to those of the adult. The results suggest that the fetal neurohypophysis and kidney may participate in the maintenance of fetal osmolar and volume homeostasis.
Flow-dependent transport processes: filtration, absorption, secretion
Authors: Wright F. S.
Published: December 2017

To define aspects common to different flow-dependent renal transport processes, four examples of such transport processes are considered: glomerular filtration, distal potassium secretion, ascending limb sodium absorption, and proximal fluid absorption. For each example the phenomenon of flow dependence is documented and the mechanism underlying this behavior is explored. Two general types of flow dependence are recognized: dissipative and generative. The first three processes are examples of dissipative flow dependence. In each a flow-sensitive component of the driving force for transport is generated upstream from the site of transport, the transport process tends to dissipate its driving force, and higher flow rates tend to maintain the driving force. The fourth process considered is an example of generative flow dependence. In this case the flow-sensitive component of the driving force is generated within the transporting segment. Flow affects the transport process by preventing dissipation of the driving force, as in the first three cases. Both types of processes can be expected to be more flow dependent in some lower range of flow rate and to be less flow dependent in some higher range of flow rate. This is because the proximate cause of a change in transport, a flow-dependent change in driving force is larger for a given change of flow rate when flow rates are relatively slow.
Renal electrolyte handling, acid-base status, and urinary acidification in Bufo marinus
Authors: Long S.
Published: December 2017

In hydrated toads reabsorption of 92% of filtered bicarbonate produces a urine of pH at 22 degrees C. Average blood-to-urine pH gradient is 0.8-0.9 U under these conditions but may reach 3-4 U. Net acid excretion rate in hydrated animals is approximately 30 mu eq . h-1 . kg-1. Flow-independent acid excretion is a negative nonlinear function of urinary pH and passes from positive to negative values in the range of normal urinary pH due to rapid rise in [HCO3-] and slower decline in [NH4+]. [H2PO4-] accounts for only 10-20% of buffer-bound acid excreted. Sulfate loading in Cl-restricted toads is without effect on blood pH but produces significant reduction in blood [Cl-]/[Na+] and in urinary pH, and increased urinary [K+] and net acid secretion rates relative to controls. These renal responses are diminished or absent during sulfate loading in Cl-rich toads. In both groups [Cl-] shows significant positive correlation with pH in sulfate-containing urines. These results are discussed in the context of the nonhomeostatic model of urinary acidification developed in mammals.
Ionic conductive properties and electrophysiology of the rabbit cortical collecting tubule
Authors: O'Neil R. G. , Boulpaep E. L.
Published: December 2017

The Na, K, and Cl conductive properties and the electrophysiological variability of the rabbit isolated cortical collecting tubule were assessed by evaluating the effect of single-ion substitutions on the transepithelial potential difference, Vte, and the transepithelial conductance, Gte. The Na permeability (and conductance) of the tight junction and basolateral cell membrane appeared to be low. However, a significant but variable amiloride-sensitive Na conductance was identified at the apical cell membrane. Although this Na conductance accounts for less than 10% of the Gte, variations in this conductance caused major alterations in the active transepithelial Na current and the Vte. A highly variable K permeability (and conductance) was also identified at the apical cell border and may account for some of the variability in Vte and Gte. This probably provides a pathway for K secretion from cell to lumen. The K permeability of the tight junction and basolateral cell membrane appeared to be relatively low. In contrast, the Cl permeability (and conductance) of the tight junction, and perhaps of the basolateral cell membrane, appeared to be high but variable and to account for the major fraction of the Gte and its variability. It is concluded that variations in the Na and K conductance of the apical cell membrane and the Cl conductance of the tight junction and basolateral cell membrane predominantly account for the variations in the electrophysiological properties of the cortical collecting tubule.
Immediate adaptation of the dog kidney to acute hypercapnia
Authors: Gougoux A. , Vinay P. , Cardoso M. , Duplain M. , Lemieux G.
Published: December 2017

Studies were performed to determine whether ammoniagenesis could adapt instantaneously to acidosis in the dog kidney. Following acute respiratory acidosis, renal glutamine extraction rose acutely in dogs with stable renal blood flow but did not change when the renal blood flow fell by more than 25%. Acute hypercapnia immediately increased renal ammonia production in both groups of dogs. The rate of both glutamine extraction and ammonia production in acutely hypercapnic dogs without hemodynamic changes was comparable to the rates observed in dogs with chronic metabolic acidosis. Furthermore, the renal metabolite profile observed in acute hypercapnia was similar to the pattern described in chronic metabolic acidosis, i.e., a marked fall in renal glutamate and alpha-ketoglutarate concentrations and a fivefold increase in malate and oxaloacetate concentrations. In the liver and muscle, acute hypercapnia induced no significant change in glutamine concentration but glutamate and alpha-ketoglutarate concentrations decreased. Our findings demonstrate that the dog kidney can adapt immediately to acidosis but that hemodynamic change may mask this adaptation.
Oxalate transport by proximal tubule of the rabbit kidney
Authors: Senekjian H. O. , Weinman E. J.
Published: December 2017

Oxalate transport was examined in isolated perfused segments of the proximal tubule of the rabbit. When oxalate was present in a concentration of 10(-5) M in the bathing and perfusing solutions, there was a net secretory flux of oxalate of 36.4 +/- 1.4, 34.7 +/- 4.3, and 20.7 +/- 2.8 x 10(-15) mol . min-1 . mm-1 in the superficial S1, S2, and S3 segments, respectively, at a bath temperature of 37 degrees C. The net secretory flux of oxalate in the juxtamedullary S1 and S2 segments was 12.8 +/- 2.5 and 12.5 +/- 3.6 x 10(-15) mol . min-1 . mm-1, respectively. Cooling to 25 degrees C resulted in a significant decrease in the net flux of oxalate. When oxalate was present in the bathing solution only (10(-5) M), the bath-to-lumen flux of oxalate was not different from the net flux in the superficial and juxtamedullary S2 segments. These studies demonstrate that oxalate undergoes net secretion in the rabbit proximal tubule. This occurs against an electrical gradient, in the absence of concentration gradients, and can be inhibited by cooling, suggesting an active transport process. There is significant internephronal heterogeneity in the proximal tubule for oxalate secretion.
Diuretic response to acute hypoxia in the conscious dog
Authors: Walker B. R.
Published: December 2017

Experiments were performed to determine the renal effects of acute hypoxia in conscious normovolemic dogs. Dogs were made hypoxic and also became hypocapnic through increased ventilation. Hypocapnic hypoxia was associated with increased urine flow, arterial blood pressure, cardiac output, PAH and inulin clearance, and electrolyte excretion. Urinary excretion of prostaglandin E2 (PGE2) also increased during hypocapnic hypoxia. To test whether the respiratory alkalosis accompanying hypoxic exposure was important in mediating the observed response, experiments were conducted in which the dogs were hypoxic but remained isocapnic via addition of CO2 to the inspired gas. Urine flow increased and was associated with changes in renal function and hemodynamics similar to those during hypocapnic hypoxia. Experiments were also conducted to determine whether the increased PGE2 release in hypoxia was functionally significant. Dogs were pretreated with meclofenamate and then made hypoxic. Prostaglandin synthesis inhibition did not alter the renal response to hypocapnic hypoxia. Dogs were also treated chronically with propranolol in an attempt to blunt the rise in blood pressure during hypoxia. In dogs with only a small transient increase in blood pressure, the diuresis was blocked. It is concluded that systemic hypoxia results in a mild diuresis in the conscious normovolemic dog. This response occurs independent of changes in arterial pH or renal prostaglandin release. The diuretic effect of hypoxia is probably due to increased renal perfusion pressure and resultant increased filtration.
Pathways for carboxylic acid transport by rabbit renal brush border membrane vesicles
Authors: Nord E. , Wright S. H. , Kippen I. , Wright E. M.
Published: December 2017

Brush border membrane vesicles were purified from rabbit renal cortex using a calcium-precipitation procedure, and the uptake of carboxylic acids was determined by a rapid-filtration method. L-Lactate, pyruvate (monocarboxylic acids), and succinate (dicarboxylic acid) demonstrated features of Na+ cotransport: enhanced initial rate (1 s) of uptake with an inward Na+ gradient compared with the Na+ -free control condition and transient accumulation of substrate within the vesicles. Kinetic parameters derived for L-lactate and succinate show that each substrate is transported via single pathway and that the two substrates exhibit marginal cross-inhibition. A range of monocarboxylic acids including pyruvate and ketone bodies appear to interact with the monocarboxylic acid carrier. The kinetics of Nat-dependent pyruvate uptake suggest at least two transport pathways-namely, that this monocarboxylate shares both the mono- and dicarboxylic acid carriers. We conclude that isolated rabbit renal microvillus membranes possess independent transport systems for mono- and polycarboxylic acids.
Renal response to captopril in conscious dogs pretreated with indomethacin
Authors: DeForrest Jack M. , Waldron Thomas L. , Antonaccio Michael J.
Published: December 2017

This study was designed to determine whether the prostaglandins mediate the renal effects of captopril in the conscious sodium-replete dog. In a group of control animals (n = 8), effective renal plasma flow (ERPF) increased from 185 ± 15 to 230 ± 12 ml/min and plasma renin activity (PRA) increased from 0.64 ± 0.15 to 12.9 ± 1.1 ng ANG I·ml-1·h-1 after captopril (10 mg/kg bolus plus 10 μg·kg-1·min-1i.v.) administration. Glomerular filtration rate (GFR) and sodium excretion (UKV) were also increased significantly following captopril treatment, whereas urine volume (V), potassium excretion (UKV), mean arterial pressure (MAP), and heart rate (HR) remained unchanged throughout the experiment. When the same dose of captopril was given to indomethacin-pretreated dogs (5 mg/kg bolus plus 2 μg·kg-1·min-1i.v.), ERPF increased from 170 ± 8 to 265 ± 18 ml/min and PRA increased from 1.2 ± 0.4 to 14.6 ± 3.0 ng ANG I·ml-1·h-11 after the captopril administration. GFR was also increased significantly after captopril, while UNaV, UKV, and V remained unchanged. These data demonstrate that the prostaglandins do not mediate the ability of captopril to increase PRA or effective renal plasma flow in this experimental model.

prostaglandins; effective renal blood flow; plasma renin activity; angiotensin II; arachidonic acid

Submitted on September 25, 1981

Accepted on June 25, 1982
Micropuncture of superficial nephrons in avian (Sturnus vulgaris) kidney
Authors: Laverty G. , Dantzler W. H.
Published: December 2017

Single nephron glomerular filtration rate (SNGFR), fluid absorption, and tubule transport of sodium, chloride, calcium, magnesium, potassium, and phosphate were evaluated under control (2.5% mannitol infusion) conditions by micropuncture of superficial, reptilian-type nephrons of European starlings (Sturnus vulgaris). SNGFR averaged 0.36 nl . min-1 . Sodium, chloride, and water were transported at equivalent rates with about 24% of the filtered load absorbed up to the point of micropuncture. Calcium was absorbed continuously along these tubules in excess of sodium and fluid, whereas magnesium appeared to undergo net secretion early and net absorption late in the tubules. Potassium transport varied considerably, with all tubules from a single bird generally showing either net potassium absorption or no net transport. In the latter group, data for a few tubules suggested net potassium secretion. For phosphate, individual tubules from a single bird were capable of either net absorption or net secretion. Mean fractional delivery of phosphate for all tubules was 1.62, but secretion rates apparently can exceed filtration rates for phosphate by as much as 6 times.
Effect of phosphate deprivation on phosphate reabsorption in rat nephron: role of PTH
Authors: Pastoriza-Munoz E. , Mishler D. R. , Lechene C.
Published: December 2017

The sites of enhanced phosphate (PO4) reabsorption after PO4 deprivation were investigated before and after infusion of parathyroid hormone (PTH) in acutely thyroparathyroidectomized rats. Animals were fed either a control PO4 diet (1.6% P) or a low PO4 diet (0.025% P) for 2 days or 7-10 days. In control rats, PTH decreased PO4 reabsorption in the proximal tubule, loop of Henle, and distal convolution. PO4 reabsorption in the proximal tubule was enhanced after 2 days of PO4 deprivation. In this group, proximal PO4 reabsorption was decreased by PTH but remained greater than in control rats (70 +/- 6 vs. 45 +/- 6 pmol/min; P less than 0.025). After PTH, PO4 reabsorption increased in the loop of Henle from 3 +/- 0.5 to 13 +/- 2 pmol/min (P less than 0.005), whereas it was unaltered in the distal convolution in PO4-deprived rats. PTH markedly increased fractional excretion of PO4 in control rats but not in PO4-deprived rats. After prolonged PO4 deprivation, PO4 reabsorption along the nephron was unaltered by PTH. These results demonstrate that acute PO4 deprivation enhances PO4 reabsorption in the proximal tubule, although the phosphaturic effect of PTH in this segment is not abolished. Resistance to the inhibitory effect of PTH on PO4 reabsorption in some portion of the loop of Henle and possibly also in the distal convolution accounts for the absence of a significant phosphaturic effect of the hormone in acutely PO4-deprived rats. Prolongation of PO4 deprivation results in unresponsiveness to PTH extending to the proximal tubule.
Basolateral membrane properties in proximal convoluted tubules of the newborn rabbit
Authors: Linshaw M. A. , Welling L. W.
Published: December 2017

We examined the properties of basolateral cell membranes in "immature" and "mature" proximal tubules and evaluated the possibility that changes in those membranes might contribute to the reported maturation of tubule function. Proximal convoluted tubules were dissected in connection with superficial glomeruli, crimped at both ends, and induced to swell by use of ouabain, low protein bathing medium, and/or collagenase. Tubules from adult animals swelled faster than tubules from 2- to 5- or 14- to 17-day-old animals. However, the basolateral cell membranes of tubules from adult animals were three- to fourfold larger in surface area than those from 2- to 17-day animals, so that the ratio of the swelling rates to the measured basolateral membrane areas remained constant during the period from newborn to adult. We conclude that the basolateral membranes "mature" only in their surface areas and that little change occurs in their intrinsic properties such as hydraulic conductivity or ion permeability.
Citrate excretion: a window on renal metabolism
Authors: Simpson D. P.
Published: December 2017

The rate of intracellular metabolism of citrate plays a major role in determining the amount of citrate excreted in the urine. Fractional excretion of citrate can be increased either by increasing intracellular citrate synthesis from precursors or by inhibiting mitochondrial citrate metabolism. Increased excretion secondary to increased synthesis of citrate occurs when citric acid cycle precursors such as malate or succinate are infused. Increased excretion resulting from inhibition of citrate metabolism occurs when malonate, maleate, or fluorocitrate is administered. Systemic acid-base changes cause striking changes in citrate clearance and metabolism. Recent evidence suggests that the effects of acid-base changes are mediated by alteration in the pH gradient across the inner mitochondrial membrane. Metabolic alkalosis causes cytoplasmic pH and bicarbonate to increase, resulting in a decrease in the mitochondrial pH gradient. This change inhibits the tricarboxylate carrier, slowing entry of citrate into the mitochondrial matrix compartment. The level of citrate in the cytoplasm increases, tubular and peritubular citrate uptake are reduced, and citrate clearance increases. Opposite changes occur in acidosis. Change in the mitochondrial pH gradient provides a sensitive mechanism for regulating renal substrate metabolism.
In vitro perfusion of the isolated dog glomerulus
Authors: Osgood R. W. , Patton M. , Hanley M. J. , Venkatachalam M. , Reineck H. J. , Stein J. H.
Published: December 2017

Recent technological advances allowing direct in vivo measurements of the determinants of glomerular ultrafiltration have greatly expanded our understanding of that process. In addition, these in vivo studies have clarified the dynamics of glomerular ultrafiltration in a number of physiologic and pathophysiologic conditions. Despite this progress, important issues remain unresolved and beyond the scrutiny of in vivo techniques. We have therefore devised a technique for in vitro glomerular perfusion of the isolated dog glomerulus. In eight glomeruli perfused at physiologic rates, the glomerular filtration rate averaged 39 nl/min and the filtration fraction was 0.19. Filtration pressure disequilibrium was observed in all studies and thus allowed calculation of a unique value for the ultrafiltration coefficient. That parameter averaged 2.34 nl/(min X mmHg). Morphologic studies employing transmission electron microscopy indicate that isolated perfused glomeruli remain ultrastructurally intact. The method for glomerular isolation and in vitro perfusion is presented in detail, the results obtained are compared with published in vivo results, and the advantages offered by the technique are discussed.
Corticosterone binding sites along the rat nephron
Authors: Lee S. M. , Chekal M. A. , Katz A. I.
Published: December 2017

Glucocorticoids influence numerous kidney functions but the precise location of glucocorticoid receptors in the nephron is not known. To identify the renal binding sites of corticosterone, the natural glucocorticoid in the rat, we measured the binding of [3H]corticosterone to discrete nephron segments microdissected from adrenalectomized rats. Highest specific binding capacity at 25 degrees C (expressed as fmol X cm-1 +/- SE) was found in the cortical collecting tubule (9.69 +/- 0.77) followed in decreasing order by the distal convoluted tubule (2.70 +/- 0.49), medullary collecting tubule (2.58 +/- 0.64), proximal convoluted tubule (1.09 +/- 0.10), and pars recta (0.57 +/- 0.08). Binding was lowest in the thick ascending limb of Henle's loop, with comparable values in the medullary (0.27 +/- 0.05) and cortical (0.26 +/- 0.05) portions of this segment. The apparent maximal binding capacity of the cortical collecting tubule for corticosterone exceeded by nearly two orders of magnitude that of aldosterone previously measured by us in this structure, which is in agreement with the observations of other investigators in kidney cytosol. Specific binding of corticosterone can be demonstrated along the entire rat nephron, but binding sites are concentrated in the cortical collecting tubule. This segment appears to be the main target site for corticosterone as it is for aldosterone.
Segmental effects of norepinephrine and angiotensin II on isolated renal microvessels
Authors: Edwards R. M.
Published: December 2017

Interlobular arteries and superficial afferent and efferent arterioles were isolated from rabbit kidney, and the effects of intraluminal pressure, norepinephrine (NE), and angiotensin II (ANG II) on lumen diameter were examined. A single microvessel was dissected and one end was cannulated. The other end of the vessel was occluded and lumen diameter was measured at fixed intraluminal pressures. With step increases in intraluminal pressure over the range of 70-180 mmHg, lumen diameters of the interlobular arteries and afferent arterioles remained constant or decreased by up to 11%. In contrast, lumen diameters of efferent arterioles continued to increase as intraluminal pressure was elevated. In all three vessels NE (10(-9) to 10(-5) M) caused a dose-dependent decrease in lumen diameter. However, only the efferent arteriole responded to ANG II (10(-12) to 10(-8) M). The contractile response of the efferent arteriole to NE or ANG II was localized to the first 50-75 micrometers of the vessel as it emerged from the glomerulus. This finding suggests that smooth muscle cells are located only in this portion of the efferent arteriole. It is concluded that at least part of the autoregulation of renal blood flow can be explained by a myogenic mechanism in preglomerular vessels and that ANG II acts primarily on postglomerular segments of the rabbit renal microcirculation.
Cell osmotic water permeability of isolated rabbit proximal convoluted tubules
Authors: Carpi-Medina P. , Gonzalez E. , Whittembury G.
Published: December 2017

Cell osmotic water permeability, Pcos, of the peritubular aspect of the proximal convoluted tubule (PCT) was measured from the time course of cell volume changes subsequent to the sudden imposition of an osmotic gradient, delta Cio, across the cell membrane of PCT that had been dissected and mounted in a chamber. The possibilities of artifact were minimized. The bath was vigorously stirred, the solutions could be 95% changed within 0.1 s, and small osmotic gradients (10-20 mosM) were used. Thus, the osmotically induced water flow was a linear function of delta Cio and the effect of the 70-microns-thick unstirred layers was negligible. In addition, data were extrapolated to delta Cio = 0. Pcos for PCT was 41.6 (+/- 3.5) X 10(-4) cm3 X s-1 X osM-1 per cm2 of peritubular basal area. The standing gradient osmotic theory for transcellular osmosis is incompatible with this value. Published values for Pcos of PST are 25.1 X 10(-4), and for the transepithelial permeability Peos values are 64 X 10(-4) for PCT and 94 X 10(-4) for PST, in the same units. These results indicate that there is room for paracellular water flow in both nephron segments and that the magnitude of the transcellular and paracellular water flows may vary from one segment of the proximal tubule to another.
In vivo metabolism of tritiated LHRH by the whole kidney and individual tubules of rats
Authors: Stetler-Stevenson M. A. , Flouret G. , Nakamura S. , Gulczynski B. , Carone F. A.
Published: December 2017

[pyroglutamyl-3,4-3H]Luteinizing hormone-releasing hormone ([3H]LHRH) and [14C]inulin were infused into individual nephrons in Inactin-anesthetized rats and the amount of radioactive label and the identity of the radioactively labeled material in urine were determined. The site of infusion was identified by latex injection and microdissection. [3H]LHRH was microinfused at 1.5 X 10(-5 M (concentration 10(6)-10(7) higher than in plasma) and analysis of urinary metabolites was performed by high-performance liquid chromatography. The urinary recovery of tritium label was 81% when proximal tubules were infused and 94% when distal tubules were infused. For proximal tubules 90% of the label recovered in urine appeared as pGlu-His (metabolite 2), pGlu-His-Trp (metabolite 3), and pGlu-His-Trp-Ser (metabolite 4), and 10% as LHRH. With distal tubules only LHRH was detected in the urine. [3H]LHRH was presented to the renal artery of the filtering rat kidney in vivo, and urine and renal venous blood were analyzed for breakdown products. The urine contained metabolites 2, 3, and 4 and no LHRH, whereas venous blood contained mainly pGlu, metabolite 4, and LHRH. When [3H]LHRH was perfused in vivo through the nonfiltering rat kidney or rat lower limb, renal or femoral venous blood was found to contain only LHRH. These studies suggest that [3H]LHRH undergoes glomerular filtration and contact digestion by brush border enzymes of the proximal tubule to produce metabolites 2, 3, and 4. These metabolites and possibly LHRH are partially reabsorbed and undergo further intracellular degradation to produce pGlu. Endothelial and interstitial cells in the kidney and leg do not appreciably metabolize [3H]LHRH.
Changes in tubular basolateral membrane markers after chronic DOCA treatment
Authors: El Mernissi G. , Chabardes D. , Doucet A. , Hus-Citharel A. , Imbert-Teboul M. , Le Bouffant F. , Montegut M. , Siaume S. , Morel F.
Published: December 2017

Chronic administration of DOCA to rabbits is known to increase the surface area of the basolateral membrane and the Na-K-ATPase activity of the cortical collecting tubule (CCT). We attempted to ascertain 1) whether Na-K-ATPase is the only basolateral membrane marker induced by DOCA, and 2) whether CCT is the only nephron segment affected by this steroid. We measured the activity of Na-K-ATPase and adenylate cyclase (AC) and the protein content of nephron segments microdissected from control and DOCA-treated rabbits. Morphogenic effects of DOCA, assessed by 30-60% increases in protein content, were specifically observed in the distal convoluted tubule, CCT, and medullary collecting tubule. When expressed as a function of tubular length, Na-K-ATPase activity rose from 80 to 200% in all these segments, whereas the increments in AC of 40-70%, observed in response to four different hormones, occurred only in some of them. When expressed as a function of protein content, Na-K-ATPase activity increased but AC activity remained unchanged. This study indicates that the morphogenic action resulting from chronic DOCA administration affects the entire rabbit distal nephron. During this action Na-K-ATPase is the preferentially induced enzyme.
Alteration of renal baroreceptor by salt intake in control of plasma renin activity in conscious dogs
Authors: Farhi E. R. , Cant J. R. , Barger A. C.
Published: December 2017

We investigated the relationship between renal arterial pressure (RAP) and systemic plasma renin activity (PRA) in five uninephrectomized conscious dogs on normal salt (80 meq Na+/day) and low salt (10 meq Na+/day) diets. The RAP was controlled by an inflatable cuff placed around the origin of the renal artery. In both salt states the PRA was an exponential function of the RAP: log (PRA) = (-0.026 X RAP) + 2 on the normal salt diet (r = 0.96) and log (PRA) = (-0.026 X RAP) + 2.5 on the low salt diet (r = 0.99). At any RAP, the value of the low salt PRA was 3 times that of the normal salt PRA. Accordingly, a reduction in salt intake increases the sensitivity of the renal baroreceptor so that the absolute value of PRA increases at any RAP, but the percentage change in PRA caused by any change in RAP is the same in both normal and low salt states.
Metabolism and transport of L-glutamine and L-alanine by renal tubules of chickens
Authors: Craan A. G. , Vinay P. , Lemieux G. , Gougoux A.
Published: December 2017

The metabolism and cellular transport of 1 and 5 mM glutamine (Gln) and alanine (Ala) and the metabolism of lactate (Lac) by renal tubular fragments of normal and chronically acidotic chickens were studied. The tubules were prepared by the collagenase digestion procedure and incubated for 0-60 min with or without substrates. Acidosis increased 1 mM Gln utilization from 1.14 to 1.74 and 1 mM Ala from 1.55 to 2.92 mumol X min-1 X g wet wt-1. Gluconeogenesis increased from 0.29 to 0.59 (Gln) and 0.44 to 1.06 (Ala), while ammoniagenesis rose from 2.19 to 3.24 (Gln) and 1.54 to 2.56 (Ala) mumol X min-1 X g-1. In contrast, Lac uptake (2.71 mumol X min-1 X g-1) and gluconeogenesis from Lac (1.05 mumol X min-1 X g-1), which equalled or exceeded the values observed with Gln or Ala in normal rats, were unchanged by acidosis. These data suggest 1) that acidosis increases gluconeogenesis from Gln and Ala by accelerating the glutamate deamination process, and 2) that the glutamate originating from glutamine and alanine are segregated in two different pools within the mitochondria with different access to glutamate dehydrogenase activity. Net cellular uptake of Gln was greater in acidotic chicken tubules, establishing an intracellular concentration of 4.5 in acidotic vs. 3.0 mM in normal chickens when 1 mM Gln was used in the incubation medium. In contrast, 1 mM alanine uptake was not modified by acidosis, greater intracellular metabolism lowering the cellular concentration of this amino acid. These observations suggest that the cellular transport of glutamine but not that of alanine is increased in tubular fragments of acidotic chickens.
Effects of pH on bone calcium and proton fluxes in vitro
Authors: Bushinsky D. A. , Krieger N. S. , Geisser D. I. , Grossman E. B. , Coe F. L.
Published: December 2017

Bone mineral is thought to decompose during acute and chronic metabolic acidosis and thereby contribute to buffering of the acid load. We cultured neonatal mouse calvariae for 3 h and found calcium efflux from bone when the medium pH was below 7.40, calcium influx into bone when the pH was above 7.40, and no net flux at pH 7.40. The calcium flux varied to the same extent when medium pH was altered by a primary change in the medium bicarbonate concentration or in the partial pressure of carbon dioxide. Calcium and proton fluxes were inversely correlated (r = -0.713, P less than 0.001), and the slope of the linear regression indicated that between 16 and 21 neq of proton entered the calvariae in exchange for each neq of calcium that left. In 24-h cultures, acid medium also caused net calcium efflux from bone, and alkaline medium caused net influx. PTH increased calcium efflux at acid but not at alkaline medium pH. Sodium azide resulted in net influx of calcium into bone at all values of medium pH. Calcium release by cultured calvariae in response to low medium pH is associated with proton buffering; over 3 h the stoichiometry indicates that little buffering is due to the dissolution of calcium-containing crystals. Effects of medium pH on calcium release are amplified by PTH, and calcium efflux can be prevented by the metabolic inhibitor sodium azide.
Effect of unilateral ureteral obstruction on metabolism of renal lipids in the rat
Authors: Tannenbaum J. , Purkerson M. L. , Klahr S.
Published: December 2017

The metabolism of lipids in the cortex and inner medulla of control and experimental kidneys of rats with unilateral ureteral obstruction (UUO) was studied in vitro. A marked increase in the tissue triglyceride content was noted after 24 h of obstruction in the experimental kidney compared with the contralateral kidney of rats with UUO and normal kidneys from sham-operated rats. A decrease in total phospholipid content was seen in the experimental kidney after 24 h of obstruction. The incorporation of [1-14C]oleic acid or [14C]arachidonic acid into tissue triglycerides was significantly increased in the cortex and medulla of the experimental kidney of rats with UUO compared with either the contralateral kidney of the same animals or kidneys from sham-operated rats. The oxidation of [1-14C]oleic acid to 14CO2 and the incorporation of [14C]arachidonic acid into tissue phospholipids or free fatty acids were significantly lower in the experimental kidney of rats with UUO. The results strongly suggest an increase in the net synthetic rate of triglycerides in the experimental kidney of UUO rats. This increase may be related to both a decrease in fatty acid oxidation and an increased release of fatty acids from phospholipids presumably due to increased phospholipase activity.
Renal nerves in renal adaptation to dietary sodium restriction
Authors: DiBona G. F. , Sawin L. L.
Published: December 2017

To assess the physiologic importance of the renal nerves in the renal mechanisms for the maintenance of body sodium balance, renal adaptation to normal and low sodium diet was evaluated in conscious Sprague-Dawley male rats before and 8 days after recovery from bilateral surgical-pharmacological renal denervation. Renal denervation was confirmed in every rat at the end of the study by absence of renal vasoconstriction to splanchnic nerve stimulation and loss of renal tissue norepinephrine content. Daily sodium balance, defined as the difference between dietary sodium intake and urinary sodium excretion, was positive with the normal sodium diet before and after bilateral renal denervation. Prior to bilateral renal denervation, changing to the low sodium diet was associated with a diminishingly negative sodium balance for 3 days that became progressively positive thereafter. After bilateral renal denervation, changing to the low sodium diet was associated with a continuous and progressively negative sodium balance. We conclude that intact renal innervation is required for normal renal sodium conservation and maintenance of body sodium balance during dietary sodium restriction.
Intracellular chloride activities in the isolated perfused shark rectal gland
Authors: Welsh M. J. , Smith P. L. , Frizzell R. A.
Published: December 2017

The isolated, perfused shark rectal gland secretes Cl when stimulated with adenosine 3',5'-cyclic monophosphate (cAMP). To investigate the mechanism of secretion, we used Cl-selective and conventional (KCl-filled) microelectrodes to measure the intracellular Cl activity (aClc). Under nonsecreting conditions, the electrical potential difference across the basolateral membrane (psi b) was -78 m V and aClc was 57 mM, a value seven times greater than predicted for electrochemical equilibrium across the basolateral membrane. When theophylline and 8-bromo-cAMP were added to the perfusate, the transglandular electrical potential difference doubled and the rate of fluid secretion increased 20-fold; however, neither psi b nor aClc changed. During both nonsecreting and secreting conditions the intracellular accumulation of Cl results in an electrochemical potential difference favoring Cl exit across the apical cell membrane. The constancy of aClc despite the variation in secretion rate suggests that stimulation is associated with an equivalent enhancement of net Cl movement across both the apical and basolateral membranes. When stimulated glands were perfused with Na-free (choline) Ringer, secretion was abolished and aClc fell toward the value predicted for electrochemical equilibrium. These findings suggest that the "uphill" step in Cl secretion lies at the basolateral membrane, where cellular Cl accumulation probably involves secondary active transport; i.e., Cl entry is driven by an inwardly directed electrochemical potential difference for Na.