bluuebunny/crossref_metadata_2025 huggingface dataset:
Osmoregulation of thirst and vasopressin release in pregnancy
Authors: Lindheimer M. D. , Barron W. M. , Davison J. M.
Published: December 2017

Osmoregulation is altered in human gestation, body tonicity declining to a nadir early in pregnancy after which a new steady-state plasma osmolality is maintained until term. Development of precise, sensitive, and specific radioimmunoassays for arginine vasopressin (AVP), which permit clearer definitions of functional properties of the osmoregulatory system, have led to a formulation of how these changes occur (both in women as well as in a gravid rat model). The osmotic thresholds for thirst and antidiuretic hormone release each decrease approximately 10 mosmol/kg during the initial weeks of human gestation. Lowering the threshold to drink stimulates increased water intake and dilution of body fluids. Because AVP release is not suppressed at the usual levels of tonicity, it still circulates and water is retained. Osmolality declines until it decreases below the osmotic thirst threshold (situated several mosmol/kg above that for hormone secretion), and a new steady state, with little change in water turnover, is established. The metabolic clearance rate of AVP is also altered, increasing three- to fourfold between gestational week 10 and midtrimester, paralleling the appearance and rapid rise in circulating cystine-aminopeptidase (vasopressinase), an observation that may explain several disorders of water handling that complicate human pregnancy. Finally, mechanisms responsible for the altered osmoregulation are obscure but chorionic gonadotropin may be involved in the changes during human gestation.
Short-term effect of aldosterone on NEM-sensitive ATPase in rat collecting tubule
Authors: Khadouri C. , Marsy S. , Barlet-Bas C. , Doucet A.
Published: December 2017

Because previous studies indicated that in the collecting tubule, N-ethylmaleimide (NEM)-sensitive ATPase, the biochemical equivalent of the proton pump, is controlled by mineralocorticoids in the long term, the present study was designed to investigate whether such control also exists in the short term. Therefore we investigated the in vivo and in vitro effects of aldosterone on the enzyme activity in cortical and outer medullary collecting tubules (CCT and MCT, respectively) from adrenalectomized rats. Administration of aldosterone (10 micrograms/kg body wt) markedly stimulated NEM-sensitive ATPase activity in the CCT and MCT within 3 h. Similarly, incubating CCT or MCT for 3 h in the presence of 10(-8) M aldosterone enhanced NEM-sensitive ATPase activity up to values similar to those previously measured in the corresponding nephron segments of normal rats. In vitro stimulation of NEM-sensitive ATPase was dose dependent in regard to aldosterone (apparent affinity constant approximately 10(-9) M), appeared after a 30-min lag period, and reached its maximum after 2-2.5 h. Finally, actinomycin D and cycloheximide totally abolished the in vitro action of aldosterone, demonstrating the involvement of protein synthesis in this process.
Effect of increases in cytosolic Ca2+ on inner medullary collecting duct cell pH
Authors: Slotki I. N. , Schwartz J. H. , Alexander E. A.
Published: December 2017

Changes in cytosolic calcium concentration (Cai2+) have been implicated in the regulation of intracellular pH (pHi) in several cell types. In the present study we investigated the mechanism by which an increase in Cai2+ stimulates H+ secretion and a rise in pHi in cultured rat inner medullary collecting duct (IMCD) cells. Confluent monolayers were made quiescent by incubation for 24 h in 0.1% serum before study. Changes in pHi and Cai2+ were measured with the fluorescent probes, 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) and fura-2. In nominally bicarbonate-free media containing 110 mM Na+ and 1 mM Ca2+, addition of the Ca2+ inophore, ionomycin (10 microM), produced a biphasic response in pHi, a transient acidification from 7.29 +/- 0.07 to 7.12 +/- 0.05 at 2 min followed by a sustained alkalinization to a steady-state value of 7.51 +/- 0.10 at 10 min. The rate of alkalinization was dose dependent. The alkalinization was not affected by 1 mM amiloride, removal of extracellular Na+, or by the proton pump inhibitor, N-ethyl maleimide (NEM). Metabolic energy was not required, but removal of extracellular Ca2+ prevented the alkalinization. By use of the fluorescent probe bisoxonol to assess membrane potential, ionomycin was shown to cause depolarization under the same experimental conditions as those for alkalinization. The Ca2+-induced alkalinization was mimicked by cell depolarization (induced by raising extracellular K+ in the presence of valinomycin 1 microM). We conclude that changes in Cai2+ are important in the regulation of pHi in the IMCD. Ca2+-induced cell alkalinization may be mediated by changes in membrane ionic conductance.
Carrier-mediated transport of tetraethylammonium across rabbit renal basolateral membrane
Authors: Montrose-Rafizadeh C. , Mingard F. , Murer H. , Roch-Ramel F.
Published: December 2017

Mechanisms of tetraethylammonium (TEA) transport were investigated in basolateral membrane (BLM) vesicles from rabbit renal cortex. Preloading vesicles with 10 mM TEA or 1 mM mepiperphenidol stimulated the 15-s uptake of [14C]-TEA compared with control vesicles (258 and 200%, respectively) and produced an overshoot of the equilibrium value (3 and 1.6 times, respectively). In the presence of a K+ gradient, net TEA uptake was also increased (and showed an overshoot of 2-fold) when the membrane potential of vesicles was made interior negative by adding valinomycin. Both TEA-TEA exchange and the voltage-driven net TEA transport were cis-inhibited by other organic cations, and a similar affinity order was found for both transport mechanisms (quinine greater than amiloride greater than morphine greater than mepiperphenidol greater than choline = N1-methylnicotinamide). This data suggests that the same transport protein might be responsible for both phenomena. Other experiments determined that the BLM vesicles had no TEA-H+ exchange, and that contamination of the vesicle population by brush-border membranes was negligible in terms of their contribution to TEA transport. These results demonstrate the presence of an exchange reaction for TEA in the rabbit renal BLM and thus imply carrier-mediated transport of TEA by these membranes.
Electrical properties of rabbit early distal convoluted tubule in primary culture
Authors: Merot J. , Bidet M. , Gachot B. , Le Maout S. , Koechlin N. , Tauc M. , Poujeol P.
Published: December 2017

Distal bright convoluted tubules (DCTb) were microdissected from rabbit kidney cortex and cultured in a hormonally defined medium. The quality and the degree of polarization of the growing epithelia were assessed by indirect immunofluorescence studies using a monoclonal antibody raised against the apical membrane of the DCTb in situ. The cultured monolayers had a high hexokinase activity and a low gamma-glutamyl transferase activity compared with cultured proximal convoluted tubules. Adenosine 3',5'-cyclic monophosphate production was stimulated by calcitonin and insensitive to parathyroid hormone, vasopressin, and isoproterenol. Both 20- and 30-day-old cultures developed an apical-negative transepithelial potential of -3.1 and -22.3 mV, respectively. Amiloride reversibly reduced the voltage by 90% only when applied on the apical side of the monolayers. Phenamil (10(-8), 10(-6) M) had the same effect as amiloride. Calcitonin reversibly decreased the transepithelial voltage. These data support the hypothesis that, in the DCTb in primary culture, the transepithelial voltage is due to the presence of Na channels and that calcitonin modulates this transport pathway.
Volume receptors in guinea pig labyrinth: relevance with respect to ADH and Na control
Authors: Bartoli E. , Satta A. , Melis F. , Caria M. A. , Masala W. , Vargiu G. , Meloni F. , Teatini G. P. , Azzena G. B.
Published: December 2017

We tested the hypothesis that changes in extracellular fluid volume are reflected by pressure changes within structures of the inner ear and that through neural pathways, a control mechanism exerts an influence on antidiuretic hormone (ADH) release and Na excretion. The study was performed on 35 guinea pigs. In protocol 1, 13 animals were studied before and after decompression of the inner ear by bilateral fluid withdrawal in an experimental setting of sustained isotonic expansion that kept the osmoreceptor partially activated and the intrathoracic volume receptors suppressed. A group of six sham-operated animals served as control. In protocol 2, nine animals were studied before and after a unilateral rise in their inner ear pressure during slightly hypertonic low-rate infusions that kept the osmoreceptor and thoracic volume receptors stimulated. A group of seven sham-operated guinea pigs served as controls. Decompression of the inner ear was attended by a rise in plasma ADH from 11.9 +/- 2.4 to 29.1 +/- 6.9 pg/ml, in urine osmolality (Uosmol) from 470 +/- 48 to 712 +/- 46 mosmol/kg (P less than 0.001), and a fall in urine flow rate (V) from 184 +/- 47 to 71 +/- 11 microliters/min (P less than 0.01), whereas plasma Na (PNa) and osmolality (Posmol) did not change. During inner ear hypertension, plasma ADH fell from 25.6 +/- 3.9 to 18.4 +/- 3.1, Uosmol from 829 +/- 58 to 627 +/- 43 (P less than 0.001), and V rose from 51 +/- 11 to 130 +/- 23 (P less than 0.001), whereas glomerular filtration rate, PNa, and Posmol did not change.(ABSTRACT TRUNCATED AT 250 WORDS)
Metabolic alterations in proximal tubule suspensions obtained from ischemic kidneys
Authors: Gaudio K. M. , Thulin G. , Ardito T. , Kashgarian M. , Siegel N. J.
Published: December 2017

A viable suspension of proximal tubules that had sustained an in vivo ischemic injury was harvested, and cellular integrity and viability were determined. The histopathological appearance of this preparation has characteristic features of an ischemic injury and ATP levels were comparable to those observed with nuclear magnetic resonance spectroscopy in vivo. Sprague-Dawley rats were subjected to 45 min of bilateral renal artery ischemia and the kidneys were allowed to reperfuse for either 15 min, 2 h, or 24 h before the harvest of the proximal tubule suspension. There was a decrease in base-line oxygen consumption from 34 +/- 0.8 nmol O2.min-1.mg protein-1 to 22 +/- 0.6 at 15 min of reflow. This decline in oxygen consumption persisted during the first 2 h of reflow and returned to control levels by 24 h. Residual respiration in the presence of ouabain was similar at all reflow intervals suggesting that the decrease in basal O2 consumption was related to decreased Na+-K+-ATPase in situ. In contrast, there was no significant difference in Na+-K+-ATPase activity when determined chemically under Vmax conditions in all experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Prostaglandin E2 inhibits Na+-K+-ATPase activity in the inner medullary collecting duct
Authors: Jabs K. , Zeidel M. L. , Silva P.
Published: December 2017

Prostaglandin E2 (PGE2) is natriuretic and inhibits collecting duct sodium transport by poorly defined mechanisms. To determine the mechanism of this inhibition, we have studied the effect of PGE2 on ouabain-sensitive (transport-dependent) oxygen consumption (QO2), ouabain-sensitive 86Rb+ uptake and ouabain-sensitive ATPase activity in fresh suspensions of rabbit inner medullary collecting duct cells, as well as Na+-K+-ATPase activity in inner medullary membranes. PGE2 (10(-5) M) reduced total QO2 by 21.6 +/- 2.3% (mean +/- SE) and reduced the ouabain-sensitive component of QO2 in IMCD cells. PGE2 failed to inhibit QO2 in the absence of sodium or in the presence of ouabain and blunted the increase in QO2 in response to amphotericin B. These results suggested that PGE2 inhibited Na+-K+-ATPase activity. Inhibition of pump activity was confirmed by measurements of 86Rb+ uptake: PGE2 (10(-5) M) reduced ouabain-sensitive 86Rb+ uptake by 57% at 10 s without altering equilibrium uptake. Furthermore, PGE2 (10(-6) M) reduced ouabain-sensitive ATPase activity by 46% in permeabilized inner medullary collecting duct cells. PGF2 alpha (10(-5) M) did not significantly alter QO2, 86Rb+ uptake, or Na+-K+-ATPase activity. These results demonstrate that PGE2 inhibits inner medullary collecting duct Na+-K+-ATPase activity and suggest a role for this inhibition in the natriuretic effect of PGE2.
Na+ electrochemical gradient and Na+-Ca2+ exchange in rat proximal tubule
Authors: Dominguez J. H. , Rothrock J. K. , Macias W. L. , Price J.
Published: December 2017

he basolateral cell membrane of the rat proximal tubule contains a Na+-Ca2+ exchanger that may participate in the regulation of cytosolic calcium (Cai) and Ca2+ transport. In this work, the activity and orientation of the Na+-Ca2+ exchanger was studied in rat proximal tubules. The experiments were based on the thermodynamic notion that the exchanger is driven by the prevalence of either of two electrochemical gradients, that for Na+ (delta mu Na+) or for Ca2+ (delta mu Ca2+). Reductions in delta mu Na+, achieved by lowering extracellular Na+ (Nao) from 150 to 15 mM, increased Cai, decreased 45Ca efflux, and increased 45Ca influx. These changes occurred concurrently. When delta mu Na+ was reduced by increasing intracellular Na+ (Nai) with 10(-3) M oubain, Cai also increased. The effect of ouabain was probably dependent on Nai accumulation because the surge in Cai was prevented by exposure of the tubules to 5 mM Nao before ouabain exposure. On the other hand, when delta mu Na+ was lowered mM Nao and then by reducing Nao to 15 mM, Cai rose in two additive stages. We conclude from these data that in the rat proximal tubule the basal state of the Na+-Ca2+ exchanger is in forward mode, Nao-Cai. Moreover, the function of the Na+-Ca2+ exchanger is in accord with predictions derived from a thermodynamic analysis of its function.
Effect of small-solute gradients on transcapillary fluid movement in renal inner medulla
Authors: Pallone T. L. , Yagil Y. , Jamison R. L.
Published: December 2017

Volume efflux from descending vasa recta (DVR) of hydropenic rats occurs despite a higher oncotic pressure than hydraulic pressure. To explain this, we previously proposed that transcapillary small-solute gradients exert an additional driving force for volume efflux. This hypothesis was tested by micropuncture of DVR at the base and tip of the exposed renal papilla of control hydropenic and furosemide-treated rats. The DVR plasma osmolality at the base, 573 +/- 40, rose to 1,011 +/- 118 mosmol/kg H2O at the tip in control animals but was 356 +/- 8 and 377 +/- 6, respectively in furosemide animals, demonstrating that the axial osmotic gradient was nearly eliminated. The DVR plasma protein concentration in control hydropenic rats was higher at the tip, 6.8 +/- 0.4 g/dl, than at the base, 5.2 g/dl (P less than 0.01), because of volume efflux from DVR between base and tip, but was 5.4 +/- 0.3 and 5.5 +/- 0.2 g/dl at the base and tip, respectively, in furosemide animals, indicating virtual abolition of volume efflux. In DVR at the tip in control animals, plasma protein concentration positively correlated with plasma osmolality (R = 0.72, P less than 0.02). These results support the hypothesis that transcapillary small-solute gradients influence transcapillary fluid movement in DVR.
Modulation of renin by thromboxane: studies with thromboxane synthase inhibitor, receptor antagonists, and mimetic
Authors: Welch W. J. , Wilcox C. S. , Dunbar K. R.
Published: December 2017

The regulation of plasma renin activity (PRA) by thromboxane (Tx) A2 was studied in anesthetized rats by measuring PRA before and after administration of drugs that block cyclooxygenase (CO) (indomethacin [INDO], 5 mg/kg), thromboxane synthase (TS) (UK 38485 [UK], 100 mg/kg), or Tx receptors (SQ 29548 [SQ], 8 mg/kg or L 641953 [L], 50 mg/kg) or that activate Tx receptors (U 46619 [U], 10 ng.kg-1.min-1). PRA (ng ANG I.ml-1.h-1) was unaffected by vehicle; it was reduced by INDO (25 +/- 2 to 13 +/- 3, n = 13, P less than 0.001) but was increased by UK (24 +/- 3 to 50 +/- 6, n = 18, P less than 0.005), SQ (27 +/- 4 to 44 +/- 7, n = 6, P less than 0.05), and L (32 +/- 4 to 51 +/- 7, n = 10, P less than 0.05). U reduced PRA in each rat (17 +/- 3 to 10 +/- 3, n = 6, P less than 0.005). UK caused dose-dependent stimulation of PRA (mean effective dose 50 mg/kg) and inhibition of TxB2 excretion (mean inhibitory dose 15 mg/kg). After INDO, SQ no longer changed PRA (-1 +/- 10, n = 7). Prolonged administration of SQ for 4-6 days (20 mg.kg-1.day-1 ip) did not change Na+ or K+ balances, blood pressure, renal hemodynamics, or urine flow. However, SQ stimulated PRA (P less than 0.007) independent of prior salt intake. In conclusion in anesthetized rats 1) PRA is stimulated by products of CO but inhibited by products of TS and by a Tx mimetic; 2) stimulation of PRA by SQ depends on ongoing PG and Tx synthesis; 3) rise in PRA with Tx antagonists is not closely related to changes in salt balance, blood pressure, or renal hemodynamics.
Distribution of major organic osmolytes in rabbit kidneys in diuresis and antidiuresis
Authors: Yancey P. H. , Burg M. B.
Published: December 2017

Sorbitol, glycerophosphorylcholine (GPC), inositol, and betaine are organic osmolytes that accumulate in renal medullary cells. Two roles have been proposed for them: 1) that all four are “compatible osmolytes” that help regulate cell volume without disturbing function, and 2) that the methylamines (GPC and betaine) are “counteracting osmolytes,” i.e., stabilizers that offset the perturbing effects of the high urea concentration. To test these hypotheses we have measured the osmolyte gradients in diuresis and antidiuresis in rabbit kidneys cut in 7 sections along the corticopapillary axis. In both antidiuresis and diuresis, inositol was highest in the outer medulla and decreased toward the tip of the inner medulla. In antidiuresis, contents of sodium, urea, sorbitol, GPC, and betaine increased monotonically toward the tip of the inner medulla. All osmolytes were significantly lower in diuresis compared with antidiuresis in two or more kidney sections. Urea, GPC, and sorbitol had the greatest differences between the two states. The sum of the four (mainly intracellular) compatible osmolytes showed a strong linear correlation with Na (presumably mostly extracellular), with a similar slope in both states, consistent with the compatible osmolytes hypothesis. Considering the osmolytes individually, only two linear correlations were highly significant and had similar slopes in both diuresis and antidiuresis: betaine with Na and GPC with urea. The latter is consistent with the counteracting osmolytes hypothesis, suggesting that GPC is the main agent stabilizing against urea in the renal medulla.
Renal calcium transport: mechanisms and regulation--an overview
Authors: Bronner F.
Published: December 2017

Renal calcium transport is described as the result of two processes, a paracellular, gradient-dependent process that predominates in most segments of the nephron and a transcellular, energy-dependent step that characterizes calcium transport in the distal convoluted tubule (DCT). Transcellular calcium transport involves entry into the DCT cell, possibly via channels, intracellular movement which appears to be facilitated by the presence of the vitamin D-dependent, cytosolic calcium-binding protein (CaBPr, calbindin D28k, mol mass approximately 28 kDa), and extrusion via the Ca-ATPase. Although much is known about calcium channels, their presence in renal tissue has only been demonstrated by preliminary studies. Quantitative data on CaBPr content of rat DCT are also unavailable, but theoretical analysis and early experimental values of intracellular self-diffusion of calcium have confirmed the need for an intracellular calcium "ferry," i.e., a molecule like CaBPr to amplify intracellular calcium movement. Available data on the plasma membrane Ca-ATPase are consistent with the extrusion kinetics attributed to the renal Ca-ATPase, but it has not been isolated, nor has its gene been cloned. Regulation and disorders of renal calcium transport are likely to involve one of the three transcellular steps, but indirect regulation by modification of the cell walls and molecules constituting the paracellular pathway cannot be excluded.
Low-dose glucocorticoids stimulate electroneutral NaCl absorption in rat colon
Authors: Bastl C. P. , Schulman G. , Cragoe E. J.
Published: December 2017

Glucocorticoids, not aldosterone, may regulate basal colonic NaCl transport. Aldosterone induces spironolactone-inhibitable, amiloride-inhibitable conductive Na absorption but basal transport is electroneutral and amiloride and spironolactone resistant. We examined in vivo the Na absorptive pathway induced by glucocorticoid receptor specific doses of glucocorticoid using various amiloride analogues. Doses of dexamethasone sufficient to co-occupy aldosterone receptors produced amiloride-sensitive Na absorption in proximal and distal colon. Low doses of dexamethasone or the specific glucocorticoid RU26988 markedly stimulated Na absorption but did so by an amiloride-resistant mechanism. The Na-H antiport inhibitor, 5-N-ethyl-N-isopropylamiloride (NENIA) eliminated glucocorticoid-induced Na and Cl absorption without changing transmural potential difference (PD) in proximal and distal colon (Ki = 0.7 x 10(-7) M). NENIA had no effect on aldosterone-induced transport. NENIA (10(-5) M) almost eliminated Na absorption in adrenal intact animals if infused early in the experimental protocol. With time, NENIA resistance developed, corresponding with the previously documented rise in endogenous aldosterone. Thus glucocorticoids induce an electroneutral Na absorptive pathway that may be the luminal Na-H antiport, suggesting that glucocorticoids regulate adrenal-dependent electroneutral Na absorption in rat colon.
Epidermal growth factor receptor regulation in rat kidney: two models of renal growth
Authors: Behrens M. T. , Corbin A. L. , Hise M. K.
Published: December 2017

The binding of 125I-labeled epidermal growth factor (EGF) to plasma membranes prepared from rat kidney cortex was studied following unilateral nephrectomy, a model of proximal tubule cell hypertrophy, and following the administration of folic acid, a model of proximal tubule cell hyperplasia. Binding of 125I-EGF was a linear function of basolateral membrane protein content and time of incubation. Specific binding to luminal brush-border membranes was not evident in these studies. Neither insulin nor insulin-like growth factor I could displace EGF binding, indicating that binding was specific. Scatchard analysis revealed a single binding site. The KD in sham-operated animals 48 h after surgery was 11.2 +/- 1.4 nM, whereas Bmax averaged 95.2 +/- 4.1 fmol/mg protein (n = 3). Similar values were obtained in nephrectomized animals. The Bmax of folic acid-untreated animals averaged 212.5 +/- 6.9 fmol/mg 48 h after administration, whereas that of vehicle-injected controls averaged 85.4 +/- 9.2 (n = 3, P less than 0.001). Differences in binding were not related to changes in affinity, ligand degradation by the preparations, or receptor binding of endogenous EGF. These data indicate that regeneration following folic acid administration is associated with an upregulation of proximal nephron EGF receptors that may play an important role in the mitogenic response.
Renal actions of atrial natriuretic factor: a mathematical modeling study
Authors: Mejia R. , Sands J. M. , Stephenson J. L. , Knepper M. A.
Published: December 2017

Atrial natriuretic factor (ANF) is a peptide hormone that increases renal NaCl and water excretion. Several renal sites of ANF action have been identified, but general agreement has not been reached concerning the quantitative contribution of each action to the natriuresis and diuresis. Using a five-nephron central core model of NaCl, urea, KCl, and water transport in the rat kidney, we have quantitatively evaluated the hypothetical effects on whole kidney function of three experimentally observed ANF actions: 1) inhibition of active NaCl absorption in the collecting duct, 2) inhibition of osmotic water permeability in the collecting duct, and 3) increased NaCl and water delivery out of the proximal convoluted tubule simulating an increase in glomerular filtration rate. The simulations show that inhibition of collecting duct active NaCl absorption by greater than or equal to 50% can increase NaCl and water excretion to levels that match experimental values. In addition, the model predicted that the urinary sodium concentration will increase to greater than plasma levels as observed experimentally. Simulated decreases in collecting duct water permeability predicted an increase in water excretion with little change in NaCl excretion. Simulated 2.5–5% increases in glomerular filtration rate also increased simulated NaCl and water excretion rates to experimentally observed levels in response to ANF. However, this action was less effective than inhibition of collecting duct active NaCl absorption in increasing the urinary NaCl concentration. We conclude that a combination of several actions are likely to account for the overall renal effect of ANF.
Molecular events in the organization of renal tubular epithelium: from nephrogenesis to regeneration
Authors: Bacallao R. , Fine L. G.
Published: December 2017

Information from studies of embryonic nephrons and established renal tubular cell lines in culture can be integrated to derive a picture of how the renal tubule develops and regenerates after acute injury. During development, the formation of a morphologically polarized epithelium from committed nephric mesenchymal cells requires an external signal for mitogenesis and differentiation. Polypeptide growth factors, in some cases mediated through oncogene expression, act in an autocrine or paracrine fashion to stimulate the production of extracellular matrix proteins that probably provide the earliest orientation signal for the cell. Interaction of these proteins with cell surface receptors leads to early organization of the cytoskeletal actin network, which is the major scaffolding for further differentiation and for definition of plasma membrane domains. The formation of cell-cell contacts via specialized adhesion molecules integrates the epithelium into a polarized monolayer and maintains its fence function, i.e., separation of plasma membrane domains. Microtubules probably participate in the delivery of vesicles to specific plasma membrane domains and in the spatial organization of intracellular organelles. Following acute renal injury, this sequence of events appears to be reversed, resulting in partial or complete loss of differentiated features. Regeneration seems to follow the same pattern of sequential differentiation steps as nephrogenesis. The integrity of the epithelium is restored by reestablishing only those stages of differentiation that have been lost. Where cell death occurs, mitogenesis in adjacent cells restores the continuity of the epithelium and the entire sequence of differentiation events is initiated in the newly generated cells.
Experimental Fanconi's syndrome resulting from 4-pentenoate infusion in the dog
Authors: Gougoux A. , Zan N. , Dansereau D. , Vinay P.
Published: December 2017

Studies were performed in anesthetized dogs to evaluate the effects of 4-pentenoate on urinary electrolyte excretion and renal metabolism. The intravenous administration of 4-pentenoate (1 mumol.kg-1.min-1 during 180 min) markedly increased the urinary excretion of bicarbonate, phosphate, potassium, amino acids, glucose, and various organic anions, whereas that of sodium and chloride also rose but less strikingly. These results suggest that 4-pentenoate markedly inhibits the proximal reabsorption of various solutes and therefore reproduces an experimental Fanconi's syndrome. Despite the rise in renal cortical concentration of alpha-ketoglutarate, glutamine utilization and total ammonia production expressed per 100 ml glomerular filtration rate increased following 4-pentenoate infusion, the ammonia being diverted into the renal vein. This increment in glutamine utilization was equal to the combined rise in the renal production of glutamate and alpha-ketoglutarate. By contrast, renal lactate utilization was drastically reduced. A causal relationship between the decreased renal cortical ATP concentration and the inhibited reabsorption of various solutes is suggested but cannot be established unequivocally.
Early adaptation of renal magnesium reabsorption in response to magnesium restriction
Authors: Shafik I. M. , Quamme G. A.
Published: December 2017

Dietary magnesium restriction with hypomagnesia is normally associated with diminished urinary magnesium excretion. Young rats were pair fed control magnesium diets (0.05% MgSO4) and magnesium-restricted diets (less than 0.01% Mg), and tubular magnesium reabsorption was assessed to determine the importance of filtered load (plasma magnesium) and to establish the presence of cellular adaptation of magnesium transport. Urinary magnesium excretion decreased from 17.2 +/- 2.7 to 5.9 +/- 1.2% over 20 h on low-magnesium diets without a change in plasma concentration (0.61 +/- 0.02 mM). This cellular adaptation was rapid (within 5 h), specific (without effect on sodium and calcium), and sensitive (without change in plasma concentration). Micropuncture studies demonstrated that cellular adaptation occurred within the loop of Henle. After 20 h, plasma magnesium fell with an associated further decrease in fractional magnesium excretion. Accordingly, cellular adaptation of magnesium transport occurs with magnesium-deficient diets, and alterations in filtered magnesium and plasma magnesium concentration are not necessary for magnesium conservation.
Y2-type receptors for peptide YY on renal proximal tubular cells in the rabbit
Authors: Sheikh S. P. , Sheikh M. I. , Schwartz T. W.
Published: December 2017

By means of primary cell cultures and luminal and basolateral membrane vesicles a single class of high-affinity binding sites for peptide YY (PYY), a member of the pancreatic polypeptide (PP)-fold family of peptides, was identified on the vascular side of the tubular epithelium in the proximal convoluted tubule of rabbit kidney. The binding of mono-iodinated radiolabeled PYY was inhibited equally well by PYY and neuropeptide Y (NPY), whereas the potency of the third member of the family, PP, was 10(5) times lower. Because NPY immunoreactive nerves in the mammalian kidney are confined to vascular smooth muscle cells and the juxtaglomerular apparatus, we propose that the physiological ligand for this binding site is blood-borne PYY. The kidney PYY receptor was sensitive to guanine nucleotides and could be classified as belonging to the Y2-subtype of NPY receptors, thus resembling in its binding characteristics the hippocampal NPY receptor. The high amounts of Y2-type PYY receptors present on the proximal tubule cell in rabbit kidney should permit studies on the functions and mechanisms of actions of PYY.
Novel recordings of renal sympathetic nerve activity in conscious fetal sheep and newborn lambs
Authors: Smith F. G. , Klinkefus J. M. , Kopp U. C. , Robillard J. E.
Published: December 2017

This study describes a technique for measuring efferent renal sympathetic nerve activity (RSNA) during the perinatal period. Experiments were carried out in four chronically instrumented fetal sheep (gestational age, 134–140 days) and 6 newborn lambs (postnatal age, 3–7 days). Surgery, performed under halothane anesthesia, consisted of routine catheter insertions and placement of a Doppler flow probe around the left renal artery. In addition, bipolar platinum electrodes were placed on a branch of the left renal postganglionic nerve. At least 24 h after surgery RSNA was measured in conscious fetal and newborn animals. RSNA was pulse synchronous, reduced with pressor agents, and completely inhibited during ganglionic blockade. Using this method, we have provided direct evidence of efferent renal sympathetic nerve traffic in utero and in the immediate postnatal period. This technique opens new avenues into the investigation of the role of the sympathetic nervous system during the perinatal period.
Characteristics of apical Cl-HCO3 exchanger of bicarbonate-secreting cells in turtle bladder
Authors: Kohn O. F. , Mitchell P. P. , Steinmetz P. R.
Published: December 2017

The apical anion exchanger of the beta-carbonic anhydrase (CA) cells differs from the basolateral exchanger of the alpha-cells by reduced sensitivity to disulfonic stilbenes and lack of immunoreactivity with antibodies to erythrocyte band 3 protein. To characterize the exchanger, we examined the effects on electroneutral bicarbonate secretion (JHCO3n) of Cl- replacement by gluconate, Br-, SO4(2-), and NO3- and of inhibition by 1) acetazolamide (ACZ) with and without pretreatment with sodium azide (NaN3), 2) furosemide, and 3) alpha-cyano-4-hydroxycinnamate (CHC). The Cl-dependent JHCO3n was 0.90 +/- 0.09 mumol/h, similar to the ACZ-inhibitable rate of 0.83 +/- 0.08 mumol/h with an apparent Km for Cl near 3.4 mM. Maximal JHCO3n was comparable at luminal pH 6.8 and 4.5. JHCO3n was reduced to approximately 21% in Br-, 13% in SO4(2-), and 7% in NO3- solutions compared with the rates in chloride solutions. ACZ inhibition was not abolished by pretreatment with NaN3. JHCO3n was only slightly inhibited (14%) by furosemide and not inhibited by CHC. In conclusion, the apical exchanger is selective for chloride and relatively resistant to inhibitors. Its dependence on luminal chloride is such that its transport rate is closely regulated by mucosal chloride at concentrations below 20 mM.
Chloride channels in the apical membrane of cortical collecting duct cells
Authors: Light D. B. , Schwiebert E. M. , Fejes-Toth G. , Naray-Fejes-Toth A. , Karlson K. H. , McCann F. V. , Stanton B. A.
Published: December 2017

Ion channels in the apical membrane of cortical collecting duct (CCD) cells in culture were studied by the patch-clamp technique. CCD cells from rabbit kidney were isolated by solid-phase immunoadsorption with a monoclonal antibody. The majority of CCD cells (93%) had phenotypic characteristics similar to intercalated cells (ICC). Although Cl- channels were present in the apical membrane of the ICC cells, they were rarely active in cell-attached patches; however, channels were activated after patch excision. In inside-out patches, the channels exhibited rapid flickering, substrates, and large unitary currents. The single-channel conductance was 303 pS, the Cl(-)-to-Na+ permeability ratio was 10:1 and the Cl(-)-to-HCO3- permeability ratio was 1.5:1. The channel was inhibited by the Cl- channel blockers 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, diphenylamine carboxylic acid, and 5-nitro-2-(3-phenylpropylamino)-benzoic acid. Although a reduction in the cytoplasmic Ca2+ concentration inhibited channel activity in both inside-out patches and cell-attached patches, alterations of Ca2+ within the physiological range did not change the channel open probability. Finally, changing the cytoplasmic pH (6.5 to 8.0) did not alter the open probability. Thus a large conductance anion channel is present in the apical membrane of CCD cells in culture. This channel may be involved in cell volume regulation or in Cl- and HCO3- secretion.
Proline transport by brush-border membrane vesicles of lobster antennal glands
Authors: Behnke R. D. , Wong R. K. , Huse S. M. , Reshkin S. J. , Ahearn G. A.
Published: December 2017

Purified brush-border membrane vesicles (BBMV) of lobster antennal gland labyrinth and bladder were separately formed by a magnesium precipitation technique. L-[3H]proline uptake was stimulated by a transmembrane NaCl gradient [outside (o) greater than inside (i)] to a greater extent in BBMV from labyrinth than those from the bladder. Detailed study of the labyrinth proline-transport processes revealed a specific dependence on NaCl, with negligible stimulatory effects by NaSCN, Na-gluconate, or KCl. A transmembrane proton gradient (o greater than i) was without stimulatory effect on proline transport. A transmembrane potential difference alone, in the presence of equilibrated NaCl and L-[3H]proline, led to net influx of the labeled amino acid, suggesting that the uptake process was electrogenic and capable of bringing about the net transfer of positive charge to the vesicle interior. Although a transmembrane Na gradient alone, in the presence of equilibrated Cl and L-[3H]proline, was able to bring about the net influx of the amino acid, a transmembrane Cl gradient alone under Na- and L-[3H]proline-equilibrated conditions was not, suggesting that only the Na gradient could energize the carrier process through cotransport, while the anion served an essential activating role. Proline influx by these vesicles occurred by the combination of at least one saturable Michaelis-Menten carrier system (apparent Kt = 0.37 mM; apparent JM = 1.19 nmol.mg protein-1.10 s-1) and apparent diffusion (P = 0.33 nmol.mg protein-1.10 s-1.mM-1). Static head analysis of the transport process suggested a cotransport stoichiometry of 2 Na:1 proline with essential activation by Cl ion.
Proton gradient-dependent renal transport of glycine: evidence for vesicle studies
Authors: Roigaard-Petersen H. , Jessen H. , Mollerup S. , Jorgensen K. E. , Jacobsen C. , Sheikh M. I.
Published: December 2017

The characteristics of renal transport of glycine by luminal membrane vesicles isolated from either proximal convoluted part (pars convoluta) or proximal straight part (pars recta) of rabbit proximal tubule were investigated. In vesicles from pars convoluta two transport systems have been characterized: a Na(+)-dependent system with intermediate affinity (half-saturation 3.64 mM) and a Na(+)-independent system that, in the presence of H+ gradient (extravesicular greater than intravesicular), can accelerate the transport of glycine into these vesicles. This is the first demonstration of H(+)-glycine cotransport across the luminal membrane of rabbit kidney proximal convoluted tubule. By contrast, in membrane vesicles from pars recta, transport of glycine was strictly dependent on Na+ and occurred via a dual transport system, namely a high-affinity (half-saturation 0.34 mM) and a low-affinity system (half-saturation 8.56 mM). The demonstration of competition between the H(+)-gradient dependent uptake of glycine, L-alanine, and L-proline, but insignificant inhibition with L-phenylalanine in vesicles from pars convoluta suggests that glycine, L-proline, and L-alanine probably share a common proton gradient-dependent transport system. In vesicles from pars recta, the Na(+)-dependent uptake of glycine was inhibited by low concentrations of L-alanine and L-phenylalanine, whereas addition of L-proline to the incubation medium did not significantly alter the uptake of glycine, suggesting that the Na(+)-dependent high-affinity system for glycine located in pars recta is shared with the high-affinity L-alanine and L-phenylalanine but not L-proline transport system.
Luminal calcium regulates potassium transport by the renal distal tubule
Authors: Okusa M. D. , Velazquez H. , Ellison D. H. , Wright F. S.
Published: December 2017

We examined the effect of changes in lumen calcium concentration on net potassium transport by distal tubules in anesthetized rats. Tubules were perfused with a control solution that resembled interstitial fluid but lacked calcium. Experimental solutions were prepared by adding varying amounts of CaCl2 to the control solution to produce solutions with free ionic calcium concentration ([Ca2+]) of 0.2, 0.4, and 0.8 mM. In paired comparisons 0.2 mM Ca2+ did not affect net potassium transport, whereas 0.4 and 0.8 mM Ca2+ each reduced potassium secretion by approximately 30%. Unidirectional potassium fluxes using 86Rb as a tracer for potassium and transepithelial voltage (VTE) were measured to characterize further the effect of calcium on potassium transport. Presence of 0.8 mM Ca2+ in the lumen did not affect unidirectional absorptive potassium flux; therefore, the decrease in net potassium flux was accounted for entirely by a decrease in unidirectional secretory potassium flux. The lumen negative VTE measured in the late distal tubule decreased during perfusion with 0.8 mM Ca2+. These results are consistent with the hypothesis that increases in lumen (extracellular) calcium concentration in the range normally present in the distal tubule reduce net potassium secretion by decreasing the electrochemical gradient for potassium secretion.
Feedback responses during sequential inhibition of angiotensin and thromboxane
Authors: Welch W. J. , Wilcox C. S.
Published: December 2017

Since thromboxane (Tx) can mediate the actions of angiotensin II (ANG II), we investigated interaction between these systems on the tubuloglomerular feedback (TGF) response. TGF was assessed from proximal stop-flow pressure (PSF) during orthograde perfusion of the loop of Henle (LH) between 0 and 40 nl/min. In the basal state, TGF was 11.3 +/- 0.8 mmHg. In series 1 experiments, it was unaltered by vehicle (+0.3 +/- 0.9 mmHg, n = 9, NS), was reduced by an ANG II antagonist, saralasin (-2.4 +/- 1.1 mmHg, n = 8, P less than 0.0005), and by a TxA2 antagonist SQ 29,548 (-4.8 +/- 0.6 mmHg, n = 11, P less than 0.0001). Both drugs together produced an additive blunting of TGF of -6.9 +/- 0.7 mmHg. In series 2 experiments, TGF was again unchanged by vehicle (+0.2 +/- 0.6 mmHg). It was reduced by -4.4 +/- 0.2 mmHg (P less than 0.0001) by an angiotensin-converting enzyme inhibitor CGS-14,824A (50 mg/kg, n = 5) and by -4.0 +/- 0.4 mmHg (P less than 0.001) by a Tx synthesis inhibitor CGS-13,080 (50 mg/kg, n = 7). Although both drugs together produced a further blunting of the response of -6.1 +/- 0.4 mmHg, this was significantly (P less than 0.001) less than additive. In both series, a response (averaging 3.5 +/- 0.3 mmHg) persisted in all rats given combined antagonists or inhibitors. In conclusion, both ANG II and TxA2 can modulate TGF-induced changes in PSF independently, and the response probably requires other system(s) in addition to ANG II and TxA2.
Amino acid transport: microinfusion and micropuncture of Henle's loops and vasa recta
Authors: Dantzler W. H. , Silbernagl S.
Published: December 2017

Amino acids appear to be reabsorbed distal to the tips of loops of Henle and may be recycled between loops and vasa recta in rat papilla. These possibilities were examined further by microinfusion and micropuncture of loops of Henle and vasa recta. To obtain information on the specificity of amino acid transport distal to the tips of the loops, ascending limbs were continuously microinfused with radioactively labeled L- and D-alanine, L-glutamate, taurine, and mannitol. About 30% of the L- and D-alanine and L-glutamate but none of the taurine or mannitol appeared to be reabsorbed. These results suggest that an acidic and a neutral amino acid are reabsorbed to a similar extent, that reabsorption is not stereospecific, but that it does not occur indiscriminately for all amino acids or for all molecules of similar size. Continuous microinfusion of ascending vasa recta with radioactively labeled L- and D-alanine suggests that amino acids may be able to move from vasa recta into tubules (apparently loops of Henle) without first entering the systemic circulation. However, micropuncture measurements of concentrations of endogenous amino acids in thin ascending limbs and adjacent descending vasa recta do not demonstrate a gradient for passive movement out of loops.
Impaired renal response to a meat meal in insulin-dependent diabetes: role of glucagon and prostaglandins
Authors: Fioretto P. , Trevisan R. , Valerio A. , Avogaro A. , Borsato M. , Doria A. , Semplicini A. , Sacerdoti D. , Jones S. , Bognetti E. , et al.
Published: December 2017

The renal response to 100 g/1.73 m2 protein load in the form of a meat meal was studied in 19 normal subjects and 35 normoalbuminuric insulin-dependent diabetic patients (IDDs) under conditions of sustained euglycemia. The area under the glomerular filtration rate (GFR) curve rose above base line by 1,904 +/- 292 in normals and 502 +/- 237 ml/1.73 m2 in IDDs (P less than 0.01). The meat meal induced a greater increment in the area under the glucagon curve in normals (14,930 +/- 186 pg.ml-1.min-1) than in IDDs (7,227 +/- 67, P less than 0.01); similarly urinary excretion of prostaglandin E2 and 6-ketoprostaglandin F1 alpha rose by 119 and 98%, respectively, in normals but only by 2% (P less than 0.01 vs. normals) and 10% (P less than 0.01 vs. normals) in IDDs. The fractional albumin clearance rose by 102 and 251% in normals and IDDs, respectively. In five normal subjects indomethacin administration abolished the GFR, glucagon, prostaglandin, and albuminuric response to meat ingestion. Glucagon replacement under indomethacin treatment failed to restore these responses. In five diabetic patients, selected for having a flat glucagon and GFR response to a meat meal, replacement of glucagon to postprandial levels increased urinary vasodilatory prostaglandins and restored a normal GFR response. Thus in normal subjects renal vasodilatory prostaglandins appear to be the final effector of the renal hemodynamic and albuminuric response to a meat meal. The prostaglandin increase is likely to be mediated under physiological conditions by a glucagon rise, which, however, has no effect per se on renal hemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of prostaglandins in the renal response to calcium infusion
Authors: Lahera V. , Fiksen-Olsen M. J. , Romero J. C.
Published: December 2017

The effects of intrarenal infusions of calcium gluconate (10 and 100 micrograms Ca.kg-1.min-1) on renal hemodynamics and on renal excretory function were studied in anesthetized mongrel dogs. In one group, the two doses of calcium were infused for 30 min each (1 ml/min). In a second group, the same doses were administered 30 min after the start of an infusion of prostaglandin (PG) inhibitors (intrarenal indomethacin, 10 micrograms.kg-1.min-1, or intravenous bolus injection of meclofenamate, 5 mg/kg). No change with physiological significance was observed during the infusion of 10 micrograms Ca.kg-1.min-1. However, the infusion of 100 micrograms Ca.kg-1.min-1 induced increases (P less than 0.05) in glomerular filtration rate (50%), sodium excretion rate (180%), and fractional excretion of sodium (160%), with respect to control precalcium values. All these changes were prevented by the concurrent administration of PG synthesis inhibitors. Urinary PGE2 and 6-keto-PGF1 alpha increased 220 and 85%, respectively, during the infusion of 100 micrograms Ca.kg-1.min-1, but both decreased (P less than 0.05) below basal levels during the concurrent administration of PG synthesis inhibitors. The infusion of 100 micrograms Ca.kg-1.min-1 decreased (P less than 0.05) renal blood flow by 16% during the administration of PG synthesis inhibitors. These results suggest that PGs are mediating the increase in hemodynamic and excretory factors induced by the intrarenal infusion of 100 micrograms Ca.kg-1.min-1.