bluuebunny/crossref_metadata_2025 huggingface dataset:
Renal folate absorption and the kidney folate binding protein. II. Microinfusion studies
Authors: Selhub J. , Nakamura S. , Carone F. A.
Published: December 2017

Surface proximal convoluted tubules (PCT) in rats were microinfused in situ with [3H]folic acid to study the role of folate binding protein (FBP) in the kidney brush-border membrane for renal conservation and transport of folate [3H]folic acid absorption was linearly related to tubular length of PCT and occurred largely in this segment of the tubule. Unlabeled folate derivatives inhibited [3H]folic acid absorption, the extent of which was dependent on the type of unlabeled folate used and its concentration. At equivalent concentrations, inhibition was most effective with unlabeled folic acid, slightly lower than with 5-methyltetrahydrofolate and least effective with methotrexate. Comparisons between [3H]folic acid absorption before and after infusion of a saturating dose of unlabeled folic acid or repetitive injections of [3H]folic acid into the same tubular site revealed continuous and rapid regeneration of unsaturated folic acid uptake sites with an apparent half-life of 28.75 +/- 8.75 s. Determination of [3H] retained in the tubule at various periods after microinfusion of [3H]folic acid revealed slow cellular disappearance with an apparent half-life of 47.3 +/- 5.4 min. It is proposed that the brush-border FBP functions as a receptor of infused folic acid and that following the binding of the ligand the folic acid/FBP complex undergoes a rapid change that results in the internalization of folic acid and regeneration of unsaturated binding sites at the membrane surface. Internalized folic acid is slowly released into renal capillaries.
Renal autoregulation: models combining tubuloglomerular feedback and myogenic response
Authors: Aukland K. , Oien A. H.
Published: December 2017

As shown previously, autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR) at varying arterial pressure may result from a myogenic response (MR) acting to maintain wall tension in each preglomerular vessel segment. We now combine MR with tubuloglomerular feedback (TGF) responding to distal tubular flow rate. The model consists of preglomerular and postglomerular resistances, glomerular filtration, and a tubular system. TGF acting on preglomerular resistance with parameters that mimic responses to single nephron distal tubular flow rate in rats and dogs failed to account for the autoregulation of RBF and GFR observed experimentally. Good autoregulation was obtained by adding preglomerular MR. In this combination, TGF is activated mainly in the lower range of autoregulation. Addition of mechanisms that increase postglomerular resistance or increase the glomerular filtration coefficient at reduced arterial pressure impairs RBF autoregulation, whereas GFR autoregulation is only slightly improved. TGF regulation of pre- and postglomerular resistance in the same direction seems compatible with good autoregulation only when combined with a preglomerular myogenic mechanism.
Na+-K+ pump in chronic renal failure
Authors: Kaji D. , Thomas K.
Published: December 2017

This review summarizes the evidence for the defect in Na+-K+ pump in chronic renal failure, considers the role of various factors in causing this defect, and discusses the clinical implications thereof. Intracellular Na is elevated in erythrocytes, leukocytes, and muscle cells from some patients with chronic renal failure (CRF). Recent evidence suggests that this elevation of cell Na may be, in large part, a consequence of decreased number of Na+-K+ pump units per cell. Maintenance dialysis over a period of weeks ameliorates the defect in intracellular Na+, and this improvement is contemporaneous with an increase in the number of Na+-K+ pump sites per cell. In erythrocytes with normal cell Na+, acute hemodialysis increases the rate of Na+ and K+ transport. Many factors such as the presence of retained toxic metabolite or circulating inhibitor in the uremic plasma, or biochemical changes produced by acute hemodialysis, may explain this finding. In cells with high cell Na+, the pump-mediated K+ transport is normalized at the expense of a raised cell Na+. The decreased muscle membrane potential in uremic subjects has been attributed to a decreased activity of Na+-K+ pump. Enzymatic Na+-K+-ATPase activity of the uremic erythrocyte, leukocyte, sarcolemma, and intestines is also decreased. We discuss the role of hormonal abnormalities and circulating inhibitors, which may cause an acute inhibition of the pump and of other factors such as K+ depletion, which may cause more chronic alterations. The implications of alteration of Na+ and K+ pump transport and raised cell Na+ on other non-pump-mediated transport pathways are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)
Cl-/HCO-3 antiporter in red cell ghosts: a kinetic assessment with fluorescent probes
Authors: London R. D. , Lipkowitz M. S. , Abramson R. G.
Published: December 2017

The pH sensitive fluorescent probe acridine orange and membrane potential-sensitive fluorescent probe acridine orange and membrane potential-sensitive fluorescent probe 3,3'-dipropylthiadicarbocyanine iodide were used to evaluate the Cl-/HCO-3 antiporter and proton and potassium conductances, respectively, in human red blood cell ghosts. Acidic, chloride-loaded ghosts alkalinized rapidly in pH 8.5 chloride-free media. Alkalinization could not be ascribed to conductive proton efflux with either depolarizing potassium influx or chloride efflux. Alkalinization was consequent to flux on the Cl-/HCO-3 antiporter: this process displayed saturation kinetics, competitive inhibition by external chloride, and inhibition by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid. The mean Kms for internal chloride, external bicarbonate, and external chloride were 2.19, 0.24, and 0.44 mM, respectively. These studies confirm both the asymmetry of this carrier and the high affinity for external HCO-3; however, the affinities for internal and external chloride are significantly greater than prior estimates. The Km for internal chloride (2.19 mM) was considerably lower than levels previously reported (20-65 mM) unless external (trans) chloride was raised above 2 mM. The present studies thus demonstrate and emphasize the critical importance of trans substrate concentration in assessing the kinetics of a carrier whose mobility is faster in the loaded than in the unloaded state.
Electrophysiological studies of primary cultures of rabbit distal tubule cells
Authors: Bello-Reuss E. , Weber M. R.
Published: December 2017

Primary monolayers grown from F1 band of a Percoll gradient centrifugation ("distal" monolayers) were studied, after confluency, 6-14 days after seeding. Transmission and scanning electron microscopy revealed that two cell types, resembling principal cells of the rabbit cortical collecting tubule (CCT) and intercalated cells of either CCT or connecting tubule, constitute approximately 96% of the monolayer. About two-thirds of the intercalated cells fluoresced when treated with fluorescent peanut lectin. Indirect specific immunocytofluorescent staining revealed fluorescence in 96% of the cells, confirming that the monolayers were derived from CCT or connecting tubule cells. Exposure of monolayers to vasopressin or isoproterenol increases adenosine 3',5'-cyclic monophosphate (cAMP) content in the cells and bathing medium, whereas parathyroid hormone was ineffective. Electrophysiological studies revealed a transepithelial voltage (VT) of -11 +/- 2 mV, and basolateral membrane voltage (Vb) of -77 +/- 5 mV (n = 20). The transepithelial electrical resistance (RT) was 1,870 +/- 250 omega X cm2 (n = 13). In three out of six monolayers, amiloride (10(-5) M) applied to the apical side produced an increase in apical membrane voltage (Va) from -71 +/- 1 to -89 +/- 9 mV) and a decrease in VT (from -10 +/- 1 to -2 +/- 1 mV). The RT did not change during amiloride exposure. Exposure of the apical membrane to 140 mM K+-depolarized Va from -67 +/- 7 to -39 +/- 11 mV (P less than 0.002) and hyperpolarized VT from -7 +/- 2 to -15 +/- 3 mV (P less than 0.005). Exposure to high K+ from the basolateral side depolarized Vb from -76 +/- 11 to -43 +/- 10 mV (P less than 0.001) and depolarized VT from -9 +/- to 8 +/- 5 mV (P less than 0.001). This preparation is suitable to study basic aspects of epithelial transport by electrophysiological methods and other techniques. The findings are consistent with several of the known properties of cortical collecting tubules from rabbits studied by the isolated perfused tubule technique.
Renal autoregulation and vulnerability to hypertensive injury in remnant kidney
Authors: Bidani A. K. , Schwartz M. M. , Lewis E. J.
Published: December 2017

The remnant kidney model is characterized by moderate hypertension, proteinuria, and progressive glomerular scarring, which are ameliorated by a low-protein diet or antihypertensive drugs. The role of renal autoregulation, in determining vulnerability to hypertensive injury was investigated. After right nephrectomy and infarction of two-thirds of the left kidney, rats were fed an isocaloric normal (NP) or low-protein (LP) diet. After 3-4 wk blood pressure was not significantly different between NP and LP rats (171 +/- 8 vs. 155 +/- 6 mmHg), but urinary protein excretion was higher in NP rats (32.3 +/- 7.3 vs. 7.0 +/- 1.2 mg/24 h P less than 0.05). Measurement of renal plasma flow and glomerular filtration rate (GFR) after graded changes in renal perfusion pressure (100-160 mmHg) demonstrated poor autoregulation in NP but not in LP rats. Morphological evidence of severe injury in the form of fibrinoid necrosis and thrombosis of arterioles and glomeruli was largely confined to NP rats and became more severe after 6-8 wk. We conclude that remnant kidney rats fed NP diet autoregulate poorly, which may account for the malignant hypertensive injury to "unprotected" glomeruli, despite only moderate systemic hypertension, and contribute to the progressive nephron loss that is encountered.
Cytosolic calcium and the action of vasopressin in toad urinary bladder
Authors: Taylor A. , Eich E. , Pearl M. , Brem A. S. , Peeper E. Q.
Published: December 2017

The effects of experimental procedures believed to increase cytosolic calcium on basal and vasopressin-stimulated osmotic water flow and transepithelial sodium transport were examined in the toad urinary bladder. Exposure of isolated toad bladders to quinidine, calcium ionophores (A23187, X537A), or low-sodium or potassium-free serosal solutions resulted in a dose-dependent decrease in the hydrosmotic response to vasopressin or exogenous adenosine 3',5'-cyclic monophosphate (cAMP). The degree of inhibition of cAMP-induced water flow induced by low-sodium or potassium-free serosal bathing media varied, and in a similar manner, with the serosal calcium concentration. The effects of quinidine sulfate (2 X 10-4 M), X537A (2 X 10(-5) M), and low serosal sodium (20 mM), but not that of A23187 (10(-5) M), were readily reversible. Exposure to quinidine (4 X 10(-4) M), A23187 (10(-5) M), X537A (5 X 10(-6) M), or low serosal sodium (2 mM) also inhibited the basal short-circuit current (SCC). Vasopressin, 4-20 mU/ml, completely overcame the inhibition of the SCC induced by quinidine, A23187, or low serosal sodium, but a submaximal dose of hormone (4 mU/ml) failed to fully reverse the inhibitory effect of X537A, 5 X 10(-6) M. These results are consistent with the view that 1) a Na-Ca exchange process operates across the basolateral surface of the granular epithelial cells of the toad urinary bladder in vivo, and 2) the level of free calcium in the granular cell cytosol plays a modulatory role in the control of apical membrane water and sodium permeability by vasopressin, and in the regulation of the basal rate of transepithelial sodium transport.
Effectiveness of a salt transport cascade in the renal medulla: computer simulations
Authors: Lory P.
Published: December 2017

Based on morphological observations, it has been concluded that the upper parts of the long descending limbs of Henle's loops should be able to secrete salts into the tubular fluid (Kriz, W. Federation Proc. 42:2379-2385, 1983). In the same article, a hypothesis is given depicting how this active transport in concert with certain characteristics of the medullary architecture might produce a transport cascade toward the papillary tip, thus supporting the accumulation of salts in this region. The effectiveness of the proposed mechanism can be judged by a mathematical model only. The computer simulations of the present study demonstrate that this mechanism indeed leads to an increase of the concentrating capability of the renal countercurrent system.
Effect of atrial natriuretic peptide on vasa recta blood flow in the rat
Authors: Kiberd B. A. , Larson T. S. , Robertson C. R. , Jamison R. L.
Published: December 2017

To determine whether synthetic atrial natriuretic peptide (ANP) increases renal medullary blood flow and if so whether the increase mediates the diuresis and natriuresis induced by ANP, inner medullary vasa recta blood flow in the exposed left renal papilla of anesthetized Munich Wistar rats weighing between 102 and 161 g was measured by fluorescence videomicroscopy. The rats were maintained in a euvolemic state by the infusion of albumin. Synthetic ANP (Auriculin B) was administered intravenously as 2.5 micrograms/kg body wt prime and as a continuous infusion of 0.2 microgram X min-1 X kg body wt-1 to the experimental group (n = 7). Within 2 min after ANP was given, urine flow and sodium excretion increased (29.4 +/- 3.8 to 50.4 +/- 5.8 microliter X min-1 X kidney wt-1, P less than 0.01, and 3.39 +/- 0.57 to 6.05 +/- 0.95 mueq X min-1 X g kidney wt-1, P less than 0.01, respectively), but vasa recta blood flow in descending (DVR) or ascending (AVR) vasa recta did not change significantly (9.5 +/- 2.3 to 10.0 +/- 2.8 nl/min in DVR and 5.3 +/- 1.0 to 6.1 +/- 1.2 nl/min in AVR). Forty-five minutes after ANP was begun, urine flow and sodium excretion increased further (77.1 +/- 11.1 microliter X min-1 X g kidney wt-1 and 12.0 +/- 2.15 mueq X min-1 X g kidney wt-1, respectively), and by this time vasa recta blood flow had increased significantly to 14.0 +/- 2.6 in DVR, P less than 0.01, and 9.8 +/- 1.2 in AVR, P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of the liver in renal hemodynamic response to amino acid infusion
Authors: Woods L. L. , Mizelle H. L. , Hall J. E.
Published: December 2017

The purpose of this study is to determine the quantitative importance of the liver in mediating the increases in renal blood flow and glomerular filtration rate (GFR) that occur after elevation of plasma amino acids. A mixture of four amine acids (Gly, Ser, Ala, Pro at 0.075 mmol X kg-1 X min-1 total) was infused intravenously into normal anesthetized dogs and into a second group of dogs after ligating all blood vessels supplying the liver and inserting a hepatic portal-femoral venous shunt. In normal dogs, renal blood flow and GFR rose by an average of 20 +/- 3 and 15 +/- 4%, respectively, after 30 min of amino acid infusion, while renal vascular resistance fell 16% from 0.51 +/- 0.16 to 0.43 +/- 0.16 mmHg X ml-1 X min. The responses of dogs in which the hepatic circulation was ligated were not significantly different from those in normal animals; renal blood flow and GFR increased by 20 +/- 3 and 31 +/- 7%, respectively, and renal vascular resistance fell 26% from 0.80 +/- 0.13 to 0.59 +/- 0.08 mmHg X ml-1 X min after 30 min of amino acid infusion. Because ligation of the blood supply to the liver did not prevent the renal hemodynamic response to amino acid infusion, it appears that the liver does not play a major role in mediating renal vasodilation during elevation of plasma amino acids.
Cellular action of arginine vasopressin in the isolated renal tubules of hypothyroid rats
Authors: Kim J. K. , Summer S. N. , Schrier R. W.
Published: December 2017

Hypothyroidism has been demonstrated to be associated with an impaired concentrating capacity and specific morphological changes in the thick ascending limbs. This study was performed to evaluate the cellular action of arginine vasopressin (AVP) in the isolated renal tubules from control (C) and hypothyroid (HT) rats. Hypothyroidism was induced by feeding aminotriazole for 4 wk. Urinary volume was higher in HT rats (C 13.5 +/- 0.9, HT 17.7 +/- 0.9 ml/24 h, P less than 0.005) and urinary osmolality was lower in HT rats (C 1,707 +/- 49, HT 1,229 +/- 35 mosmol/kgH2O, P less than 0.001). Plasma AVP levels were significantly higher in HT rats (C 1.93 +/- 0.59, HT 4.12 +2- 0.62 pg/ml, P less than 0.05), thus documenting AVP resistance. The adenylate cyclase response to AVP (10(-6) M) was significantly lower (P less than 0.02) in the medullary thick ascending limb of Henle's loop (mTALH) in HT (14.3 +/- 2.4 to 41.7 +/- 5.8 fm X 30 min-1 X mm-1, P less than 0.001) than in mTALH in C rats (14.4 +/- 2.8 to 110.1 +/- 24.9 fm X 30 min-1 X mm-1, P less than 0.001). In contrast, the adenylate cyclase response to AVP was not significantly different in collecting tubules of cortex, outer medulla, and inner medulla from C and HT rats, although a slight decrease in response to AVP was observed in cortical and outer medullary collecting tubules.(ABSTRACT TRUNCATED AT 250 WORDS)
Glomerular dynamics in the hypothyroid rat and the role of the renin-angiotensin system
Authors: Gillum D. M. , Falk S. A. , Hammond W. S. , Conger J. D.
Published: December 2017

Munich-Wistar rats underwent thyroidectomy (TX) with reimplantation of the parathyroid glands. Systemic hemodynamic and micropuncture studies were performed at 1 and 3 wk post-TX, and the results were compared with levothyroxine replaced controls (TXT4). Cardiac output (CO) in TX rats fell progressively and was 40% of that in TXT4 at 3 wk. Renal blood flow declined in parallel with CO. Systemic blood pressure did not fall in TX rats because of a 50% increase in systemic vascular resistance by 3 wk post-TX. Glomerular dynamics were not significantly different between TX and TXT4 rats at 1 wk; however, by 3 wk single-nephron glomerular filtration rate (SNGFR) had fallen to 16.5 +/- 1.1 vs. 34.1 +/- 3.4 nl/min in TXT4 controls (P less than 0.001). In 3-wk TX rats, glomerular plasma flow (QA) was 50.9 +/- 3.7 vs. 108.0 +/- 8.7 nl/min in TXT4 rats (P less than 0.001), net hydraulic ultrafiltration pressure (delta P) was 33 +/- 2 vs. 37 +/- 1 mmHg in TXT4 rats (P less than 0.01), and the ultrafiltration coefficient (Kf) was 0.025 +/- 0.003 vs. 0.084 +/- 0.008 nl X s-1 X mmHg-1 in TXT4 controls (P less than 0.001). Although the changes in systemic and glomerular hemodynamics were progressive over 3 wk, proximal tubular reabsorption fell maximally within 1 wk. Similar patterns of alterations in glomerular dynamics are known physiological consequences of angiotensin II (ANG II).(ABSTRACT TRUNCATED AT 250 WORDS)
Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct
Authors: Star Robert A. , Burg Maurice B. , Knepper Mark A.
Published: December 2017

Page F1148: Robert A. Star, Maurice B. Burg, and Mark A. Knepper. “Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct.” We regret that an error was made in the title of this article. The correct title and the article are reprinted in the August 1987 issue of this journal.
Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct
Authors: Star Robert A. , Burg Maurice B. , Knepper Mark A.
Published: December 2017

We measured bicarbonate, ammonia, and luminal pH in segments of the rabbit outer medullary collecting duct (OMCD) to determine the relationship between luminal pH and ammonia transport. Both the inner-stripe and outer-stripe portions of the OMCD absorbed bicarbonate at high rates. The outer stripe OMCD generated an acidic pH disequilibrium that was reversibly dissipated by exogenous luminal carbonic anhydrase. In contrast, the inner stripe OMCD did not generate a spontaneous pH disequilibrium unless perfused with the carbonic anhydrase inhibitor acetazolamide. Ammonia secretion was three times more rapid in the outer stripe OMCD than in the inner stripe OMCD. We conclude the following. 1) Both the inner-stripe and outer-stripe portions of the rabbit OMCD secrete protons at substantial rates. 2) Functional luminal carbonic anhydrase is present in the inner stripe OMCD but absent from the outer stripe OMCD. 3) Ammonia secretion occurs predominantly by NH3, diffusion in both portions. 4) The luminal pH disequilibrium, which is normally present in the outer stripe OMCD, enhances ammonia secretion.

ammonia; ammonium; bicarbonate; diffusion trapping; nonionic diffusion; carbonic anhydrase; disequilibrium pH; fluorescence spectroscopy; hydrogen ion secretion; carbonic acid; acetazolamide; heterogeneity

Submitted on September 15, 1986

Accepted on January 15, 1987
Purification of rat papillary collecting duct cells: functional and metabolic assessment
Authors: Stokes J. B. , Grupp C. , Kinne R. K.
Published: December 2017

Rat renal papillary collecting duct (PCD) cells were isolated using collagenase and hyaluronidase digestion and a three-step low-speed centrifugation. As assessed by binding of the lectin Dolichos biflorus and determination of vasopressin-sensitive adenylate cyclase and Na+-K+-ATPase, the enrichment of PCD cells over a crude papillary cell preparation was 1.8, 2.4, and 1.4, respectively. Microscopic evaluation indicated that the preparation was greater than 90% pure PCD cells. The isolated cells were viable as evident from the high K/Na ratio of intracellular electrolytes measured by electron probe analysis (5.3), from the high ATP/ADP ratio (2.15), and the metabolic response to alterations in Na transport. Exposure to 2 mM ouabain or removal of Na reduced O2 consumption by 25-35%; the uncoupler carboxylcyanide-m-chlorophenylhydrazone more than doubled O2 consumption. In the presence of 14 mM glucose and at a PO2 of 100 Torr the cells produced substantial quantities of lactate. This aerobic glycolysis may account for greater than 20% of the ATP production. In the presence of rotenone, glycolysis increased by 56% and was able to maintain the cellular ATP level at 65% of control. In the absence of any exogenous substrate PCD cells respired normally and had a close to normal ATP content, but lactate production was markedly decreased. These results demonstrate that viable PCD cells can be isolated from rat kidney. At normal PO2 and in the presence of D-glucose the cells show a substantial amount of aerobic glycolysis, although their mitochondrial respiration is not rate limiting. In the absence of glucose the cells derive the majority of their energy from an as yet unidentified endogenous substrate.
Dynamics of NAD in cortical nephron segments: effect of nicotinamide and of dietary phosphate intake
Authors: Yusufi A. N. , Kiebzak G. M. , Kusano E. , Werness J. L. , Homma S. , Dousa T. P.
Published: December 2017

NAD content and the rate of NAD hydrolysis were determined in proximal convoluted tubules (PCT), proximal straight tubules (PST), and adjacent cortical nephron segments microdissected from kidneys of thyroparathyroidectomized (TPTX) rats. In the basal state, rats fed a normal phosphate diet had an NAD content higher in PCT, PST, and in cortical ascending limb (CAL) than in glomeruli. After intraperitoneal injection of nicotinamide, the NAD content increased significantly in all nephron segments except CAL; the greatest (delta + 277%) increase was found in PCT, with less (delta + 82%) in PST. In experiments conducted on TPTX rats stabilized on a low-phosphorus diet, NAD content increased in response to a nicotinamide injection in PCT (delta + 197%), but did not change significantly in PST. The catabolism of NAD was determined by generation of [3H]adenosine, a major metabolite of [adenine-2,8-3H]NAD. The rate of [3H]adenosine generation from [3H]NAD was significantly (P less than 0.001) higher in PST than in PCT. We conclude that, in response to nicotinamide administration in vivo, the NAD content increases more in PCT than in PST and that this difference may be, at least partly, due to a lower rate of NAD breakdown in PCT. In a state of dietary phosphate deprivation, NAD also increases significantly in response to intraperitoneal nicotinamide in PCT, but it does not increase significantly in PST. The nicotinamide-elicited increase of NAD content in proximal tubules, mainly in PCT, may be related to inhibition of Na+-gradient-dependent inorganic phosphate (Pi) reabsorption across the brush-border membrane of proximal tubules and to the phosphaturic effect of nicotinamide in rats fed normal-Pi diet.
Alterations of enzymatic activities along rat collecting tubule in potassium depletion
Authors: Imbert-Teboul M. , Doucet A. , Marsy S. , Siaume-Perez S.
Published: December 2017

This study was designed to correlate morphological alterations induced in rat collecting tubule by potassium depletion with changes in the activity of enzymatic markers of the cell basolateral membrane. Results show the following responses. 1) Potassium depletion induced a huge and progressive hypertrophy of the outer medullary collecting tubule (MCT). Hypertrophy was paralleled by enhancements of vasopressin- and forskolin-dependent adenylate cyclase (AC) activities. Glucagon-sensitive AC was also increased, but with a different kinetics, whereas isoproterenol-dependent AC was only modestly stimulated. 2) In cortical (CCT) and papillary collecting tubules, AC response to hormones did not change. The concentrating defect of K-deprived rats, therefore, does not appear to result from an intrinsically defective adenylate cyclase system in any portion of the collecting tubule. Decreased AC response of the medullary thick ascending limb to vasopressin and glucagon, observed after 3-5 wk of K depletion, might account, at least in part, for reduced hypertonicity of medullary tissue. 3) Na+-K+-ATPase activity fell in CCT, probably in relation to decreased K secretion. Conversely, in MCT, Na+-K+-ATPase rose much more than tubular volume. The physiological significance of this latter observation remains to be established.
Determinants of mitochondrial O2 dependence in kidney
Authors: Aw T. Y. , Wilson E. , Hagen T. M. , Jones D. P.
Published: December 2017

The O2 dependence of mitochondrial cytochromes was studied in suspensions of isolated rat kidney cells to examine the determinants of renal mitochondrial function. Direct spectroscopy of the oxidation of cytochromes c + c1, a + a3, and b561 + b566 showed that oxidation-reduction changes of the entire electron transport chain occur over the same range of O2 concentrations; this suggests that the mitochondrial cytochromes function as a single unit in response to O2 changes. Half-maximal oxidation (P50 value) of cytochrome c + c1 in intact cells was 3.6 microM but was only 0.45 microM in isolated renal cortex mitochondria under state 3 conditions. This is consistent with the existence of a substantial O2 concentration gradient from the extracellular space to the region around the mitochondria under hypoxic conditions. Comparison with results for digitonin-treated cells under state 3 conditions indicates that the distribution of mitochondria within the cellular structure is an important determinant of the cellular O2 dependence. In addition, the mitochondrial O2 dependence varies as a function of cellular respiration rate. Stimulation of the O2 consumption with either a protonophore, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, or a sodium ionophore, nystatin, increased the P50 value. Conversely, inhibition of ATP consumption by Na+-K+-ATPase with ouabain, or inhibition of mitochondrial electron transport with antimycin A, decreased the P50 value. Thus the O2 concentration required for mitochondrial function in the kidney is affected by mitochondrial distribution within the cell as well as by the functional demands imposed on the cell.
H+ gradient-driven dipeptide reabsorption in proximal tubule of rat kidney. Studies in vivo and in vitro
Authors: Silbernagl S. , Ganapathy V. , Leibach F. H.
Published: December 2017

Microinfusion of glycylsarcosine into superficial nephron sections showed that the dipeptide was reabsorbed mainly in late portions of the rat proximal tubule. In vivo microperfusion data demonstrated a saturable, high-capacity, low-affinity dipeptide reabsorption mechanism that was inhibited by other peptides but not by amino acids or peptidase inhibitors. The reabsorption was enhanced by lowering the luminal pH from 7.5 to 5.5. In vitro studies with rat cortical brush-border vesicles showed that glycylsarcosine uptake was independent of a Na+ gradient and greater uptake occurred when the extravesicular pH was acidic compared with the intravesicular pH. An inward-directed H+ gradient stimulated glycylsarcosine uptake and caused a transient accumulation of the dipeptide inside the vesicles above the equilibrium value. The presence of a proton ionophore abolished the H+ gradient-dependent uptake. An inside-negative membrane potential stimulated the initial uptake of the dipeptide. The uptake process was saturable and inhibited by other peptides but not by amino acids. The vesicle studies also showed that there are at least two peptide transport systems functioning in these vesicles, one a high-affinity, low-capacity type and the other a low-affinity, high-capacity type.
Epoxygenase metabolites of arachidonic acid inhibit vasopressin response in toad bladder
Authors: Schlondorff D. , Petty E. , Oates J. A. , Jacoby M. , Levine S. D.
Published: December 2017

In addition to cyclooxygenase and lipoxygenase pathways, the kidney can also metabolize arachidonic acid by a NADPH-dependent cytochrome P-450 enzyme to epoxyeicosatrienoic acids (EETs); furthermore, 5,6-EET has been shown to alter electrolyte transport across isolated renal tubules. We examined the effects of three EETs (5,6-, 11, 12-, and 14,15-EET) on osmotic water flow across toad urinary bladder. All three EETs reversibly inhibited vasopressin-stimulated osmotic water flow with 5,6- and 11,12-EET being the most potent. The effects appeared to be independent of prostaglandins. EETs inhibited the water flow response to forskolin but not (with the exception of 11,12-EET) the response to adenosine 3',5'-cyclic monophosphate (cAMP) or 8-BrcAMP, consistent with an effect on cAMP generation. For 11,12-EET the question of an additional inhibition at a site beyond or independent of cAMP has to be considered. To determine whether these effects were due to the EETs or to products of their metabolism, we examined the effects of their vicinal diol hydrolysis products, the dihydroxyeicosatrienoic acids. Nonenzymatic conversion of labeled 5,6-EET to its vicinal diol occurred rapidly in the buffer, whereas 11,12-EET was hydrolyzed in a saturable manner only when incubated in the presence of bladder tissue. The dihydroxyeicosatrienoic acids formed inhibited water flow in a manner paralleling that of the EETs. Both 5,6-EET and 11,12-EET (10(-5) M) prevented the increase in intracellular cAMP content observed in control tissues after vasopressin stimulation. Finally, 11,12- and 14,15-dihydroxyeicosatrienoic acid inhibited vasopressin- and forskolin-stimulated adenylate cyclase in the same rank order as their inhibition of water flow.(ABSTRACT TRUNCATED AT 250 WORDS)
Potassium secretion by nonsensory region of gerbil utricle in vitro
Authors: Marcus N. Y. , Marcus D. C.
Published: December 2017

The isolated nonsensory region of the gerbil utricle in vitro produced a lumen-positive transepithelial electrical potential difference (VT) of +5.7 mV and a luminal fluid containing 106 mM K when bathed in mammalian Ringer solution (5 mM K and 150 mM Na). The lumen of this region was perfused in vitro with K-free solution and the luminal [K], VT, and transepithelial resistance (RT) were measured before and following perfusion under control conditions and after addition of bumetanide (0.1 mM) or ouabain (1 mM) to the bath. The perfusate contained a reduced [Ca], since the average value of utricular endolymph in vivo (0.28 +/- 0.03 mM) measured with Ca-selective microelectrodes was 38% of that in perilymph. Under control conditions, the luminal [K] initially increased at a rate of 2.13 mumol X cm-2 X h-1 after perfusion; net secretion continued until the luminal [K] returned to its preperfusion level. This flux rate corresponds to 57 microA/cm2. The “equivalent short-circuit current” (Equiv. Isc; VT/RT) was found to average 61 microA/cm2. Both K secretion and VT were fully inhibited by bumetanide and by ouabain. Luminal application of Ba (5 mM) in K-free solution had no effect on the initial rate of K secretion, but did prevent full recovery of luminal [K] to the control level. These results are the first estimates of K secretion by the nonsensory cells of the utricle and are the first to directly demonstrate inhibition of K secretion in the inner ear by bumetanide and in the nonsensory tissue of the utricle by ouabain.
Hepatic denervation alters first-phase urinary sodium excretion in dogs with cirrhosis
Authors: Levy M. , Wexler M. J.
Published: December 2017

Cirrhotic dogs without intrahepatic hypertension (IHH) never retain sodium or expand plasma volume. To test the hypothesis that IHH may cause urinary sodium retention early in cirrhosis, we prepared cirrhotic dogs (chronic biliary obstruction) who underwent simultaneous hepatic denervation with end-side portacaval anastomoses. Such animals, along with appropriate controls and unanesthetized were studied by balance techniques. In the experimental group, plasma volume never increased, and sodium retention did not occur until 2 days prior to the appearance of detectable ascites. In a sham-denervated group, plasma volume increased by 10% and sodium retention occurred on the average 8.4 days prior to ascites. When the portal veins were left intact, the sham-denervated group showed the usual magnitude of plasma volume expansion observed in cirrhotic dogs (18.3%) with a 7-day delay between sodium retention and ascites appearance. Those dogs with hepatic denervation demonstrated a 9.2-day delay with 12.6% expansion of plasma volume. When ascites was mobilized with a peritoneovenous valve, and dogs were subjected to a high salt diet (130 meq/day), denervated dogs excreted the load normally, whereas sham-denervated dogs retained sodium and developed anasarca. We conclude that in cirrhotic dogs with IHH, liver denervation prevents early non-volume-related sodium retention.
Facilitatory role of efferent renal nerve activity on renal sensory receptors
Authors: Kopp U. C. , Smith L. A. , DiBona G. F.
Published: December 2017

The effects of decreasing and increasing efferent renal nerve activity (ERNA) on the renorenal reflex responses to stimulation of renal mechanoreceptors (MR) (increased ureteral pressure) or renal chemoreceptors (CR) (retrograde ureteropelvic perfusion with 0.9 M NaCl) were examined in anesthetized rats. During prevailing ERNA, renal MR stimulation increased ipsilateral afferent renal nerve activity (ARNA) from 6 to 41 counts/s (spike counter) (n = 37) and from 2 to 6 resets/min, (voltage integrator) (n = 23), contralateral urine flow rate from 5.3 to 7.4 microliters . min-1 . g-1 (n = 38) and urinary sodium excretion from 0.7 to 1.1 mumol . min-1 . g-1 (n = 38) (all P less than 0.01), without affecting mean arterial pressure or contralateral glomerular filtration rate. Similar results were obtained with renal CR stimulation. Decreasing ERNA 74+/- 4% by hexamethonium, 10% body weight isotonic saline volume expansion, or inflation of a balloon at the junction of right atria and superior vena cava abolished the increase in ipsilateral ARNA and the contralateral diuresis and natriuresis produced by stimulation of renal MR or CR. Increasing ERNA 254+/- 120% (peak response, n = 15, P less than 0.01) by placing the rat's tail in 53 degrees C water increased basal ARNA 249+/- 80% (n = 6, P less than 0.05) and enhanced the ipsilateral ARNA response 202+/- 78% (n = 9, P less than 0.01) to renal MR stimulation. These results indicate that ERNA exerts a facilitatory effect on renal MR and CR and their afferent renal nerve fibers in the renorenal reflexes.
Structure and development of the glomerular capillary wall and basement membrane
Authors: Abrahamson D. R.
Published: December 2017

The renal glomerular epithelium, Bowman's capsule, and tubule originate from a condensate of mesenchymal cells induced to undergo epithelial differentiation by a branch of the uretic bud. These nephrogenic cells aggregate and begin synthesizing the basement membrane molecules collagen type IV, heparan sulfate proteoglycans, and laminin as shown by immunofluorescence microscopy. Soon, the primitive nephron is invaginated by mesenchymal cells that establish the glomerular endothelium. Electron microscopy, metabolic labeling, and immunocytochemical techniques show that the endothelium and epithelium of early stage glomeruli each synthesize a basement membrane that appears to fuse, giving rise to the glomerular basement membrane (GBM). As development progresses, however, bulk GBM biosynthesis by the endothelium greatly diminishes or ceases. In contrast, GBM assembly by the epithelial podocytes continues and segments of new GBM appear beneath developing foot processes. In vivo labeling experiments with anti-laminin antibodies have shown that this new GBM derived from podocytes is subsequently spliced into existing GBM as capillary loop diameters expand. Molecular mechanisms for basement membrane fusion or splicing are not presently known but may involve partial enzymatic digestion and specific binding interactions among GBM components. The developing glomerular capillary wall, which filters plasma from very early stages, becomes decreasingly permeable to perfused macromolecules such as ferritin or immunoglobulin as the glomerulus matures. Evidence from immunolabeling studies showing that some monoclonal IgGs bind to the GBM only at specific developmental stages also indicates that temporal biochemical changes take place during GBM assembly. Such changes could include molecular rearrangement during basement membrane fusion and splicing and/or enzymatic and compositional modifications during maturation of the filtration barrier.
Distribution of IGF receptors in the plasma membrane of proximal tubular cells
Authors: Hammerman M. R. , Rogers S.
Published: December 2017

To characterize the distribution of receptors for insulin-like growth factors I and II (IGF I and II) in the plasma membrane of the renal proximal tubular cell, we measured binding of 125I-labeled IGF I and 125I-labeled IGF II to proximal tubular basolateral and brush-border membranes and characterized IGF I-stimulated phosphorylation of detergent-solubilized membranes. 125I-IGF I bound primarily to a 135,000 relative molecular weight (Mr) protein and IGF II to a 260,000 Mr protein in isolated membranes. Binding of 125I-IGF I was severalfold greater in basolateral than in brush-border membranes. IGF I-stimulated phosphorylation of the 92,000 Mr beta-subunit of its receptor could be demonstrated only in basolateral membranes. These findings are consistent with an asymmetrical distribution of receptors for IGF I in the plasma membrane of the renal proximal tubular cell, localization being primarily on the basolateral side. In contrast, binding of 125I-IGF II to isolated basolateral and brush-border membranes was equivalent, suggesting that receptors for this peptide are distributed more symmetrically in the plasma membrane. Our findings suggest that the actions of IGF I in proximal tubule are mediated via interaction of circulating peptide with specific receptors in the basolateral membrane. However, our findings establish the potential for actions of IGF II to be exerted in proximal tubule via interaction with both basolateral and/or brush-border membrane receptors.
NMR monitoring of intracellular sodium in dog and rabbit kidney-tubules
Authors: Boulanger Y. , Vinay P. , Boulanger M.
Published: December 2017

23Na-nuclear magnetic resonance (NMR) was used to monitor intra- and extracellular sodium in suspensions of dog cortical tubules, rabbit cortical tubules, and dog thick ascending limbs. The NMR visibility of the intracellular sodium was determined by comparing the NMR and flame photometry results and by redistributing the sodium ions between the intra- and extracellular compartments using the ionophore nystatin (influx) or sodium substitution for choline in the extracellular fluid (efflux). The intracellular sodium visibility was approximately 30% for the total sodium and 58% for the transportable sodium. Addition of sodium to sodium-depleted homogenates of dog renal cortex also showed a loss of visibility. The values of the relaxation times T1 and T2 were determined but could not be correlated with the visibility measurements. The intracellular sodium concentration in dog cortical tubules incubated in optimal biochemical conditions was estimated at 51 mM and was dependent on the extracellular sodium concentration.
Na+-H+ exchanger in proximal cells isolated from kidney. II. Short-term regulation by glucocorticoids
Authors: Bidet M. , Merot J. , Tauc M. , Poujeol P.
Published: December 2017

The purpose of this study was to investigate the acute regulation by glucocorticoid of the Na+-H+ exchanger in isolated renal proximal cells of the rabbit. The changes of intracellular pH (pHi) were determined in a bicarbonate-free buffer by the use of a fluorescent pH probe that may be trapped intracellularly, 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). The activity of the Na+-H+ exchanger was estimated by measuring the Na+-induced H+ efflux in BCECF-loaded cells acid loaded with nigericin in choline medium. The uptake of 1.5 mM 22Na was also studied in Na+-depleted cells. Acute application of dexamethasone (1 h at 37 degrees C) increased the activity of the Na+-H+ exchanger. Evidence for this was the fact that the hormone enhanced the rate of Na+-dependent H+ efflux in acid-loaded cells and increased the Na entry in normal pH, sodium-depleted cells. These actions were blocked by 0.5 mM amiloride and were specific to glucocorticoids, since mineralocorticoids (aldosterone) did not promote modification either of the H+ efflux or the Na influx. The effect on the kinetics of amiloride-sensitive Na+-H+ exchange indicated that dexamethasone (DEX) increased the activity by increasing the Vmax of the carrier for external sodium (Vmax control = 26.5 +/- 1.7, DEX = 33.0 +/- 2.4 mmol H+.1-1.min-1, n = 5, P less than 0.001) and for external H+ (Vmax control = 20.6, DEX = 25.8 mmol H+.1-1.min-1, n = 2).(ABSTRACT TRUNCATED AT 250 WORDS)
Atrial natriuretic peptide, right atrial pressure, and sodium excretion rate in the rat
Authors: Fried T. A. , Ayon M. A. , McDonald G. , Lau A. , Inagami T. , Stein J. H.
Published: December 2017

This study examined the relationship between right atrial pressure (RAP), urine flow rate, sodium excretion rate, and plasma atrial natriuretic peptide (ANP) levels after an acute Ringer expansion. Two groups of rats had their RAP monitored and balloon catheters placed in their thoracic inferior venae cavae. In one group the balloon remained deflated, and in the second group the balloon was inflated during the volume expansion in an attempt to prevent the rise in RAP. The peak RAP was 7.3 +/- 0.8 mmHg when the balloon remained deflated and 3.5 +/- 0.6 mmHg in the group with the balloon catheter inflated (P less than 0.005). The corresponding peak ANP levels were 682 +/- 140 and 223 +/- 40 pg/ml. There was a significant correlation between the peak RAP and ANP levels (r = 0.754; P less than 0.05). The inflation of the balloon catheter significantly decreased the urine flow rate and the urine sodium excretion rate. A final group of animals had 200 microliters of rabbit serum containing antibody to ANP infused before the volume expansion. The antibody-treated animals had significantly lower urine flow and sodium excretion rates than nonantibody-treated control rats. We conclude that ANP is one of the factors which allows the rat to excrete an acute Ringer expansion.
Effects of altered NaCl intake on renal hemodynamic and renin release responses to RNS
Authors: Osborn J. L. , Kinstetter D. D.
Published: December 2017

Relationships between frequency of renal nerve stimulation (RNS) and renal blood flow (RBF), glomerular filtration rate (GFR), and plasma renin activities (PRA) were evaluated in anesthetized dogs placed on low (5 meq/day)-, normal (40 meq/day)-, and high (200 meq/day)-sodium chloride diets. Arterial pressure, RBF, GFR, and renal venous and arterial PRA were determined before and during direct electrical RNS at 0.5, 1.0, and 2.0 Hz (15 V, 1.0 ms). Dogs on low sodium intakes increased renal venous PRA at 0.5, 1.0-, and 2.0-Hz RNS, whereas dogs on normal sodium intakes did not increase renal venous PRA until RNS reached 2.0 Hz. High sodium dogs did not increase PRA at any frequency of RNS tested. RNS at 0.5 Hz was not associated with any changes in GFR or RBF in any of the groups. Dogs on normal sodium and high sodium intakes decreased both GFR and RBF during 1.0- and 2.0-Hz RNS. Low-sodium dogs, however, only decreased GFR and RBF during 2.0-Hz RNS, and these hemodynamic responses were significantly less than 2.0-Hz GFR and RBF responses of high sodium dogs. These data indicate that renal vasoconstrictor responses to RNS are potentiated, and renin release responses to RNS are reduced by elevation of sodium chloride intake. We suggest that during low sodium intake, activation of sympathetic nerve activity elicits an enhanced renin release response, whereas the renal vasculature may be protected against neurogenic vasoconstriction.
Atriopeptins decrease resting and hormone-elevated cytosolic Ca in cultured mesangial cells
Authors: Hassid A.
Published: December 2017

The purpose of this work was to investigate the effects of atrial peptides on the cytosolic Ca levels of cultured, adherent, mesangial cells. Resting Ca levels, measured by the use of fura-2, were dose-dependently decreased by up to 30%, by atriopeptin 23. The half-maximal effect was elicited by approximately 30 pM atriopeptin-23. Atriopeptin 21 also decreased resting Ca levels by up to 30%, but this peptide was approximately 30-fold less potent than atriopeptin 23. Atriopeptin 23 (100 nM) inhibited both the Ca transient and the peak Ca value elicited by 1 nM vasopressin, but the atrial peptide had no significant effect on the Ca transient elicited by higher vasopressin concentrations. At concentrations lower than 100 nM, atriopeptin 23 had no effect on the vasopressin-induced Ca transient. Atriopeptin 23 also decreased the Ca transient and the peak Ca value elicited by 100 nM angiotensin II. Similar to vasopressin, the angiotensin II-induced Ca transient was inhibited by 100 nM but not lower concentrations of atriopeptin 23. In contrast to the effect of atriopeptin 23, atriopeptin 21 (100 nM) had no effect on the Ca transient elicited by vasopressin. These results demonstrate that atriopeptins function as modulators of resting and, under certain conditions, of hormone-increased Ca levels in cultured mesangial cells.