bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and regulation of renin in human cultured mesangial cells
Authors: Chansel D. , Dussaule J. C. , Ardaillou N. , Ardaillou R.
Published: December 2017

Renin activity was measured in the incubation medium, and the cellular extract of human mesangial cells, which had been cultured in the presence of renin-free human plasma (three kidneys; 4-7 passages). Active renin and total renin obtained after trypsin treatment was estimated by radioimmunoassay of angiotensin I using renin-free human plasma as a substrate. Mesangial cell renin had characteristics similar to those of standard human renin; optimum enzymatic activity at pH 5.8, marked inhibition in the presence of two (monoclonal and polyclonal) human renin-specific antibodies and of SR 42128, a new potent statine-containing renin inhibitory peptide. The synthetic capability of the mesangial cells varied markedly with the original kidney (1-49 and 0.3-0.9 ng X h-1 X mg-1 for total renin in the medium and the cellular extract respectively). Renin was secreted mainly as inactive renin. Prostaglandin E2 (PGE2) and carba-prostaglandin I2 (PGI2) (a stable analogue) produced a dose-dependent (0.1-1.10 microM) increase in renin activity in both the cellular extract and the culture medium. Isoproterenol (200 microM) increased renin activity only in the medium. The effects of these agonists were more marked on inactive than on active renin. These results demonstrate that cultured human mesangial cells synthesize and release renin in a stable manner over a long period of culture, thus providing a useful tool for the in vitro study of renin secretion and its control.
Adenosine inhibits beta-adrenoceptor but not DBcAMP-induced renin release
Authors: Deray G. , Branch R. A. , Herzer W. A. , Ohnishi A. , Jackson E. K.
Published: December 2017

The purpose of these studies was to assess the direct effect of adenosine on the renin release response to beta-adrenoceptor activation in vivo in the canine kidney. In an initial study, innervated, intrarenal beta-adrenoceptors were activated selectively via renal nerve stimulation in kidneys in which the alpha-adrenoceptor response to renal nerve stimulation had been blocked with phentolamine. Adenosine, infused directly into the renal artery (10 and 30 micrograms/min), significantly blunted the renin release response to renal nerve stimulation. However, adenosine also caused significant reductions in base-line glomerular filtration rate, sodium excretion rate, and filtration fraction. To eliminate these confounding effects of adenosine on renal function and to prevent changes in norepinephrine release due to prejunctional inhibition by adenosine, we also studied the effect of intrarenal infusions of adenosine on norepinephrine-induced renin release in the nonfiltering, alpha-adrenoceptor-blocked, canine kidney. In this model of beta-adrenoceptor activation, adenosine abolished the renin release response to intrarenal infusions of norepinephrine. In a final series of experiments, the effect of adenosine on the renin response to dibutyryl-adenosine 3',5'-cyclic monophosphate (cAMP) was examined in the nonfiltering, beta-adrenoceptor-blocked, canine kidney. In this model of cAMP-induced renin release, adenosine was ineffective in attenuating the renin release response. These data demonstrate that in vivo adenosine directly inhibits beta-adrenoceptor-mediated renin release by a mechanism that does not involve a reduction in the ability of cAMP to activate intracellular mechanisms leading to renin release.
Direct toxic effect of the radiocontrast agent diatrizoate on renal proximal tubule cells
Authors: Humes H. D. , Hunt D. A. , White M. D.
Published: December 2017

The pathophysiology of radiocontrast agent-induced acute renal failure is presently unclear. To test for a possible direct deleterious effect of diatrizoate, a commonly used radiocontrast agent, on renal tubule cells, suspensions enriched in rabbit proximal tubule segments were incubated with sodium diatrizoate. After these manipulations, a variety of well-established metabolic parameters to quantitate the extent of cell injury were measured. Diatrizoate sodium (25 mM) produced significant declines in tubule K+, ATP, and total adenine nucleotide (TAN) contents, significant decreases in tubule basal and uncoupled respiratory rates, and a significant increase in tubule Ca2+ content, demonstrating the development of cell injury induced by diatrizoate. These effects were dose related and were progressive with increasing incubation time from 97.5 to 157.5 min. The effects of N-methylglucosamine (meglumine) on renal tubule cell viability was also evaluated. Meglumine is a low molecular weight amino-substituted cationic compound and is commonly added to radiocontrast dye solutions. Meglumine (25 mM) had significant effects to lower tubule K+ content and to decrease both tubule basal and uncoupled respiratory rates. These alterations were slightly additive to diatrizoate in that meglumine diatrizoate produced greater alterations in tubule-metabolic parameters compared to diatrizoate sodium. A period of 22.5 min of hypoxia also caused deleterious changes in each of these quantitative indices of cell viability, and diatrizoate potentiated the degree of hypoxia-induced cell injury. These results demonstrate that the radiocontrast agent, diatrizoate, is directly toxic to renal proximal tubule cells. Meglumine, a cation added to diatrizoate containing radiocontrast solutions, also had a moderate toxic effect on renal epithelial cells and added to the toxicity of diatrizoate. Diatrizoate also aggravated the degree of cell injury induced by a 22.5-min period of hypoxia. These experiments thus provide evidence for a direct toxic effect of diatrizoate on proximal renal tubule cells which was additive to hypoxic cell injury.
Effects of vitamin D-induced chronic hypercalcemia on rat renal cortical plasma membranes and mitochondria
Authors: Levi M. , Molitoris B. A. , Burke T. J. , Schrier R. W. , Simon F. R.
Published: December 2017

Increases in intracellular and mitochondrial calcium content that accompany ischemic and toxic acute renal failure have been suggested to mediate renal tubular cell injury and dysfunction, but the mechanism(s) are unknown. We studied the effects of in vivo vitamin D-induced chronic hypercalcemia on rat renal cortical brush-border and basolateral membranes and mitochondria. In the brush-border membrane, hypercalcemia caused significant decreases in alkaline phosphatase-specific activity, total phospholipid molar content, and phosphatidylserine percent molar composition and increases in the cholesterol-to-total phospholipid molar ratio and phosphatidylinositol percent molar composition. In the basolateral membrane, hypercalcemia caused significant decreases in Na+-K+-ATPase-specific activity and total phospholipid molar content and increases in the cholesterol-to-total phospholipid molar ratio and phosphatidylinositol 4,5-bisphosphate percent molar composition. In the mitochondria, hypercalcemia caused a mild increase in the mitochondrial calcium content, but no alterations in succinic dehydrogenase-specific activity, succinate-, ADP-, or uncoupler-induced respiration. Thus hypercalcemia caused alterations in brush-border and basolateral membrane enzyme activity and lipid composition, but no functional changes were detected in mitochondria. These hypercalcemia-induced plasma membrane biochemical alterations may be markers of early cell injury and suggest a role for calcium in causing or predisposing to renal tubular cell injury.
Total CO2 flux in isolated collecting tubules during carbonic anhydrase inhibition
Authors: Laski M. E.
Published: December 2017

These studies evaluated the effects of sodium transport inhibitors on total CO2 flux (JtCO2) in the rabbit cortical collecting tubule after inhibition of carbonic anhydrase. When ouabain was added to tubules during carbonic anhydrase inhibition, reabsorptive JtCO2 rose and potential difference (PD) decreased. Amiloride added to perfusate after carbonic anhydrase inhibition decreased PD and did not alter JtCO2. If ouabain was added to an ethoxyzolamide-treated tubule with amiloride present in perfusate, no effects were detectable. Amiloride added to the bath of ethoxyzolamide-treated tubules in high concentration (10-3 M), decreased potential and increased JtCO2. If amiloride was added to the bath of cortical collecting tubules from fasted rabbits, JtCO2 rose. This response was not seen in cortical tubules from fed animals or in medullary collecting tubules. These data demonstrate the existence of carbonic anhydrase-independent acidification in this segment in vitro. The data from studies with amiloride in the presence of intact carbonic anhydrase are consistent with action on a basolateral sodium-proton exchange mechanism. A cellular model that postulates a basolateral sodium-proton exchanger in an acidifying cell is offered.
Comparison of effects of forskolin, cAMP, and vasopressin on Pf/Pd(w) of toad urinary bladder luminal membrane
Authors: Levine S. D. , Jacoby M.
Published: December 2017

We have reported that Pf/Pd(w) (the ratio of osmotic and diffusional water permeabilities) for the luminal membrane of toad urinary bladder is approximately 17 for tissues stimulated with either vasopressin or 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP). In a recent abstract, Kachadorian and co-workers have shown that tissues stimulated with adenosine 3',5'-cyclic monophosphate (cAMP) or forskolin have a lower Pf than would be anticipated from the frequency of aggregates visualized on the flat portion of the luminal membrane using freeze-fracture electron microscopy. We report here measurements of Pf/Pd(w) for the luminal membrane of tissues receiving these agents: Pf/Pd(w) for submaximally stimulated tissues was the same, regardless of whether the stimulant was vasopressin (12.7 +/- 0.3), forskolin (13.7 +/- 0.9), or cAMP (12.0 +/- 1.3). The calculated Pd(w)'s for the series barrier were also identical (6.8 +/- 0.5, 6.5 +/- 0.3, and 8.2 +/- 1.0 X 10(-4) cm/s respectively). Our data, taken together with those of Kachadorian et al. are consistent with a number of possibilities: because our methodology does not permit estimation of Pf for the series barrier, we cannot rule out the possibility of a "post-luminal barrier" that is rate-limiting for Pf, but not for Pd(w) in forskolin- and cAMP-stimulated tissues, Pf and Pd(w) of the luminal surface aggregates could decrease in parallel, so that luminal membrane Pf/Pd(w) remains constant, and there could be a diminished frequency of fused aggregate-rich aggrephores, but not of aggregates that are on the flat portion of the luminal membrane. Only the latter can be unequivocally quantitated using freeze-fracture electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)
Metabolic derivatives of aldosterone
Authors: Morris D. J. , Brem A. S.
Published: December 2017

Metabolism of aldosterone during the latent period prior to the action of the hormone may be of physiological importance. In the rat, liver metabolizes aldosterone in a sex-dependent manner; larger quantities of neutral polar and reduced aldosterone derivatives are found in male rat kidney; correlating with the larger physiological responses of male rats to aldosterone. The target tissues, mammalian kidney and toad urinary bladder, are also capable of metabolizing aldosterone in situ to neutral polar, 5 alpha- and 5 beta-reduced, and monosulfate derivatives. The 5 alpha-reduced metabolites possess significant antinatriuretic activity and are preferentially synthesized by rat kidney nuclei. The metabolic pathways leading to the synthesis of 5 alpha-reduced metabolites and their subsequent neutral polar derivatives appear to be regulated by dietary sodium and can be inhibited by antimineralocorticoids. At concentrations somewhat higher than aldosterone, these 5 alpha-reduced metabolites also can recreate the development of hypertension and suppress plasma renin activity in young adrenalectomized spontaneously hypertensive rats. Thus, several of the metabolically transformed aldosterone derivatives can be correlated with physiological regulation and/or expression of the actions of the hormone.
Oscillations in the proximal intratubular pressure: a mathematical model
Authors: Holstein-Rathlou N. H. , Leyssac P. P.
Published: December 2017

This study presents a dynamic continuous time model of the regulation of the renal proximal intratubular pressure in the rat. The model integrates a functional model of the glomerulus, a tubular model, a feedback model, and an afferent arteriolar model. The model has one equilibrium solution for the dependent variables (equilibrium point) for each set of independent variables. An equilibrium point, chosen to be in accordance with experimental data from Sprague-Dawley rats, was used as the initial value for the dependent variables. The model is shown to have parameter ranges in which sustained stable oscillations in proximal pressure are present. For sustained oscillations to appear, it is necessary for the system's operating point to be located on a sufficiently steep portion of the tubuloglomerular feedback curve. The model analyses are compared with various experimental recordings of the proximal intratubular pressure. The model simulations show both spontaneous and induced oscillations in the proximal pressure in close agreement with the experimental results; but the steady-state mean pressure regulation is found to be less efficient in the model than that apparent from the experimental recordings, suggesting the involvement of additional pressure-regulating mechanisms other than those included in the present model. It is concluded that the dynamic systems approach used in the present study yields new insight into the mechanisms underlying the proximal intratubular pressure oscillations and that it can be of further value for the study of the factors regulating the proximal intratubular pressure.
Transepithelial and intracellular potentials in isolated Malpighian tubules of tenebrionid beetle
Authors: Nicolson S. W. , Isaacson L. C.
Published: December 2017

Malpighian tubules of Onymacris plana (Coleoptera: Tenebrionidae) have been isolated for measurement of transepithelial and intracellular potentials, before and during stimulation of fluid secretion. In a bathing medium resembling the hemolymph composition of the insect, the transepithelial potential (VT) was approximately 13 mV, lumen positive. VT was subject to drift and frequently showed super-imposed regular oscillations, which were apparently action potentials associated with contractions of muscle fibers running along the tubules. Although tubules of Onymacris are approximately 8 cm long, the basal membrane potential (Vb) did not vary with distance along the tubule, averaging -31 mV. Addition of adenosine 3',5'-cyclic monophosphate (cAMP) or diuretic hormone (DH) homogenate to the bathing medium had no effect on Vb, but opposing effects on VT: cAMP caused it to increase to 60 mV, whereas DH homogenate caused a rapid drop in VT to almost zero. Ion substitutions in the bathing medium showed that under control conditions beetle tubules possessed appreciable basal permeability to both K and Cl ions, with a 10-fold reduction in bath K concentration hyperpolarizing Vb by 54 mV. The basal K and Cl channels were partially blocked by barium and thiocyanate ions, respectively. Stimulation with cAMP increased the apical membrane potential (Va) and significantly reduced the Cl permeability of the basal membrane, whereas its Na permeability remained negligible.
Effects of adenosine infusion into renal interstitium on renal hemodynamics
Authors: Pawlowska D. , Granger J. P. , Knox F. G.
Published: December 2017

This study was designed to investigate the hemodynamic effects of exogenous adenosine in the interstitium of the rat kidney. Adenosine or its analogues were infused into the renal interstitium by means of chronically implanted capsules. Infusion of adenosine (bolus 0.5 mumol plus 0.1 mumol/min) decreased glomerular filtration rate (GFR) from 0.81 +/- 0.06 (mean +/- SE) to 0.37 +/- 0.06 ml/min while having no effect on renal blood flow (RBF). The metabolically stable analogue, 2-chloradenosine (2-ClAdo), (bolus 10 nmol plus 2 nmol/min) decreased GFR from 0.73 +/- 0.07 to 0.21 +/- 0.06 ml/min. Interstitial infusion of theophylline, an adenosine receptor antagonist, completely abolished the effects of adenosine and 2-ClAdo on GFR. The distribution of adenosine, when infused into the renal interstitium, was determined using radiolabeled 5'-(N-ethyl)-carboxamidoadenosine (NECA), a metabolically stable adenosine agonist. After continuous infusion, [3H]NECA was distributed throughout the kidney. The effects of NECA to reduce GFR were similar to those of adenosine and 2-ClAdo. We conclude that increased levels of adenosine in the renal interstitium markedly decrease GFR without affecting RBF in steady-state conditions. The marked effects of adenosine agonists during their infusion into the renal interstitium and the complete blockade of these effects by theophylline suggest an extracellular action of adenosine.
Inner medullary collecting duct function during rebound alkalemia
Authors: Bengele H. H. , McNamara E. R. , Schwartz J. H. , Alexander E. A.
Published: December 2017

Rats, made acidemic when fed NH4Cl, become alkalemic with discontinuation of the NH4Cl. This phenomenon has been called rebound metabolic alkalemia (RMA). This study examines the function of the inner medullary collecting duct (IMCD) during RMA. Rats drank only 1.5% NH4Cl for 5 days and then water for 16 h prior to study, yielding an arterial pH = 7.50 +/- 0.01, PCO2 = 39 +/- 1 mmHg, and bicarbonate = 29.5 +/- 1.0 mM. The IMCD data were obtained by microcatheterization from deep (1.5-3.0 mm) and tip (0.2-0.5 mm) samples. Equilibrium pH decreased from 5.92 +/- 0.09 (n = 20) to 5.38 +/- 0.04 (n = 20) and PCO2 increased from 32 +/- 1 to 38 +/- 1 mmHg between deep and tip samples. Bicarbonate delivery decreased from 37 +/- 8 to 7 +/- 1 nmol/min. Titratable acid and ammonium delivery increased from 284 +/- 52 to 347 +/- 62 nmol/min and from 549 +/- 38 to 685 +/- 40 nmol/min, respectively. Calculated net acid excretion increased from 796 +/- 88 to 1,026 +/- 95 nmol/min. Thus during RMA, proton secretion continues along the IMCD, although there is a systemic alkalemia. It appears that factors in addition to systemic acid-base parameters are important in the regulation of proton secretion by the IMCD.
Inner medullary hemodynamics in dogs with aortocaval fistula
Authors: Chou S. Y. , Faubert P. F. , Epstein E. M. , Blackstock D. G. , Porush J. G.
Published: December 2017

To investigate the role of medullary hemodynamics and vasoactive hormones in sodium retention in dogs with aortocaval fistula, we examined papillary plasma flow (PPF), solute content, and renal output of renin, norepinephrine, and prostaglandin E2 (PGE2) in anesthetized normal and fistula dogs. During hydropenia, cardiac output was elevated and systemic vascular resistance reduced in fistula dogs, accompanied by markedly increased renal output of renin, norepinephrine, and PGE2. In fistula dogs the blunted diuretic and natriuretic response to saline loading was not due to impaired myocardial contractility. During hydropenia and after saline loading, glomerular filtration rate (GFR) and renal blood flow were similar in normal and in fistula dogs; however, PPF was significantly lower in fistula dogs, accompanied by significantly greater papillary tissue osmolality and sodium content. These findings indicate that in fistula dogs enhanced medullary sodium reabsorption is associated with decreased PPF and stimulation of the renin-angiotensin and adrenergic nervous system. Furthermore, the reduced PPF obviates medullary solute washout during saline loading, and may contribute to the blunted diuretic and natriuretic response.
Blunted natriuresis to atrial natriuretic peptide in chronic sodium-retaining disorders
Authors: Koepke J. P. , DiBona G. F.
Published: December 2017

Renal responses to atrial natriuretic peptide were examined in conscious dogs with congestive heart failure (tricuspid insufficiency) and in conscious rats with nephrotic syndrome (adriamycin). Heart-failure dogs displayed elevated atrial pressure and heart weights, blunted natriuresis to a saline load, and ascites. Nephrotic rats displayed proteinuria, hypoproteinemia, sodium retention, and ascites. In control animals, atrial natriuretic peptide increased absolute and fractional urine flow rate and urinary sodium excretion. Although atrial natriuretic peptide increased absolute and fractional urine flow rate and urinary sodium excretion in conscious heart-failure dogs and nephrotic rats, the responses were markedly blunted. In heart-failure dogs, infusion of atrial natriuretic peptide increased plasma concentrations of norepinephrine and epinephrine. In nephrotic rats, renal denervation reversed the blunted diuretic and natriuretic responses to atrial natriuretic peptide. Mean arterial pressure, glomerular filtration rate, and p-aminohippurate clearance were affected similarly by atrial natriuretic peptide in heart-failure dogs or nephrotic rats vs. control animals. Conscious congestive heart-failure dogs and conscious nephrotic rats have blunted diuretic and natriuretic responses to atrial natriuretic peptide.
Renin secretory effects of N6-cyclohexyladenosine: effects of dietary sodium
Authors: Churchill P. C. , Rossi N. F. , Churchill M. C.
Published: December 2017

Previous observations by others have shown that Na deprivation augments and Na loading attenuates the inhibitory effect of exogenous adenosine on renin secretion in vivo. The purpose of the present experiments was to test the hypothesis that Na deprivation and Na loading alter the sensitivity of the adenosine receptors (A1 subclass) that mediate the inhibitory effect. The rat renal cortical slice preparation was used. Na loading decreased and Na deprivation increased tissue renin content and the basal renin secretory rate; these two variables were directly related (r = 0.84, P less than 0.00005). N6-cyclohexyladenosine (CHA), an adenosine analogue that selectively activates the A1 subclass of adenosine receptors in the nanomolar to micromolar concentration range inhibited renin secretion over the same range of concentrations (nM-microM) and to approximately the same maximal extent (to 50% of the mean basal secretory rate) in cortical slices taken from Na-loaded, control, and Na-deprived rats. These results demonstrate that changes in the intrinsic sensitivity of adenosine receptors do not explain dietary Na-induced changes in the in vivo renin secretory response to exogenous adenosine.
Enhanced glomerular filtration and Na+-K+-ATPase with furosemide administration
Authors: Scherzer P. , Wald H. , Popovtzer M. M.
Published: December 2017

To evaluate the effect of furosemide on kidney function, glomerular filtration rate (GFR), urinary Na excretion (UNaV), Na reabsorption (NAR), and Na+-K+-ATPase in isolated nephron segments were measured in 1) rats treated with furosemide 10 mg X 100 g-1 X 24 h-1 ip for 7 days, and 2) rats receiving an oral Na load for 12 days. In furosemide-treated rats, GFR rose from 0.61 +/- 0.03 (mean +/- SD) to 0.83 +/- 0.06 ml/min (P less than 0.01), UNaV rose from 904 +/- 71 to 1,402 +/- 85 mueq/day (P less than 0.001), and net NAR rose from 87.5 +/- 3.7 to 116.7 +/- 9.0 mueq/min (P less than 0.01). Na+-K+-ATPase remained unchanged in the proximal convoluted tubule (PCT), proximal straight tubule (PST), cortical thick ascending limb of Henle's loop (cTALH), and medullary thick ascending limb of Henle's loop (mTALH), but was increased in the distal convoluted tubule (DCT) and in cortical collecting duct (CCD) from 48.5 +/- 1.2 to 75.3 +/- 0.7 (P less than 0.001) and from 18.6 +/- 0.7 to 27.1 +/- 2.7 (P less than 0.02) X 10(-11) mol X mm-1 X min-1, respectively. In Na-loaded rats GFR rose from 0.61 +/- 0.04 to 0.86 +/- 0.03 ml/min (P less than 0.001), UNaV rose from 1,064 +/- 118 to 18,532 +/- 2,045 mueq/day (P less than 0.001), net NAR from 88.1 +/- 3.0 to 107.8 +/- 3.9 mueq/min and Na-K-ATPase in the mTALH rose from 40.3 +/- 1.4 to 56.2 +/- 2.11 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Quinidine effect on hydrosmotic response of collecting tubules to vasopressin and cAMP
Authors: Lorenzen M. , Frindt G. , Taylor A. , Windhager E. E.
Published: December 2017

Quinidine, a compound thought to increase cytosolic calcium ion activity, has been found to inhibit the hydrosmotic response to vasopressin (VP) and adenosine 3',5'-cyclic monophosphate (cAMP) in the toad urinary bladder. To test whether this drug has a similar action in the mammalian nephron, the effect of quinidine on the hydraulic conductivity of the isolated perfused rabbit cortical collecting tubule (CCT) exposed to either 20 microU/ml VP or 10(-4) M 8-(p-chlorophenylthio) - adenosine 3',5' - cyclic monophosphate (8-CPT-cAMP) was studied. Quinidine had no effect on the basal water permeability of the CCT. Quinidine sulfate (10(-4) M) reduced the VP-stimulated water permeability from 280 +/- 50 X 10(-7) to 115 +/- 41 X 10(-7) cm X s-1 X atm-1 (P less than 0.05). The hydrosmotic response to 8-CPTcAMP was likewise reduced following exposure to quinidine. This effect was shown to be dose dependent. In paired experiments, inhibition of the response to 10(-4) M 8-CPTcAMP averaged 11% at 10(-6) M, 27% at 5 X 10(-6) M, 53% at 5 X 10(-5) M, and 50% at 10(-4) M quinidine. Inhibition of the response to 8-CPTcAMP was estimated to be half maximal at approximately 5 X 10(-6) M quinidine. Tubules were protected against the quinidine-induced inhibition by the addition of 6.5 X 10(-5) M quin 2-acetoxymethylester in the presence of low peritubular Ca concentration. These results are consistent with the view that elevated cytosolic Ca ion levels inhibit the increase in water permeability elicited by VP or exogenous cAMP in the mammalian CCT.
ADP activates protooncogene expression in renal epithelial cells
Authors: Kartha S. , Sukhatme V. P. , Toback F. G.
Published: December 2017

Purine nucleotides, particularly adenosine diphosphate (ADP), are the most potent mitogens known for monkey kidney epithelial cells of the BSC-1 line. To explore the molecular mechanisms by which ADP exerts its mitogenic effect, we tested the hypothesis that stimulation of DNA synthesis in these renal cells is mediated by activation of protooncogenes. Transcripts of the c-Ha-ras protooncogene were identified in quiescent, high density cells. Addition of ADP to the culture medium stimulated protooncogene expression fourfold. Maximal expression of c-ras was observed by 12 h after exposure to ADP, and preceded the initiation of DNA synthesis. Expression of the c-myc protooncogene was not detected in unstimulated cells, but accumulated maximally after 1 h of exposure to ADP. As with ADP-stimulated expression of the c-ras protooncogene, transcripts of the transferrin receptor gene reached a maximal value at 12 h, whereas the abundance of gamma-actin mRNA was not altered for up to 24 h. The results indicate that exogenous ADP stimulates protooncogene expression before initiation of DNA synthesis in renal epithelial cells in culture. These findings suggest that some physiological effects of this adenine nucleotide could be mediated by proteins specified by protooncogenes.
H+-L-proline cotransport by vesicles from pars convoluta of rabbit proximal tubule
Authors: Roigaard-Petersen H. , Jacobsen C. , Iqbal Sheikh M.
Published: December 2017

The mechanism of renal transport of L-proline by luminal-membrane vesicles isolated from proximal convoluted tubules of rabbit kidney was studied. It was found that H+ gradient (extravesicular greater than intravesicular) can drive the transport of L-proline into the vesicles both in the presence and absence of Na+. The stimulation of L-proline uptake by a pH gradient was additive with that produced by Na+. Saturation kinetic experiments revealed that pH gradient, in addition to Na+, increased the maximal uptake of L-proline by twofold. This is the first demonstration of H+-L-proline cotransport across luminal membrane of rabbit kidney proximal convoluted tubule. The physiological importance of this system is briefly discussed.
Amiloride interacts with renal alpha- and beta-adrenergic receptors
Authors: Howard M. J. , Mullen M. D. , Insel P. A.
Published: December 2017

We have used radioligand binding techniques to assess whether amiloride and certain analogues of amiloride (ethylisopropyl amiloride and benzamil) can bind to adrenergic receptors in the kidney. We found that amiloride could compete for [3H]rauwolscine (alpha 2-adrenergic receptors), [3H]prazosin (alpha 1-adrenergic receptors), and [125I]iodocyanopindolol (beta-adrenergic receptors) binding in rat renal cortical membranes with inhibitor constants of 13.6 +/- 5.7, 24.4 +/- 7.4, and 83.6 +/- 13.5 microM, respectively. Ethylisopropyl amiloride and benzamil were from 2- to 25-fold more potent than amiloride in competing for radioligand binding sites in studies with these membranes. In addition, amiloride and the two analogues competed for [3H]prazosin sites on intact Madin-Darby canine kidney cells and amiloride blocked epinephrine-stimulated prostaglandin E2 production in these cells. We conclude that amiloride competes for binding to several classes of renal adrenergic receptors with a rank order of potency of alpha 2 greater than alpha 1 greater than beta. Binding to, and antagonism of, adrenergic receptors occurs at concentrations of amiloride that are lower than previously observed “nonspecific” interactions of this agent.
Na and nonelectrolyte entry into inner ear fluids of the rat
Authors: Sterkers O. , Ferrary E. , Saumon G. , Amiel C.
Published: December 2017

Kinetics of hydrophilic solute entry into endolymph (EL), perilymph (PL), and cerebrospinal fluid (CSF) were studied after intravenous administration (sodium, urea, glycerol, mannitol, sucrose) and cerebral lateral ventricle injection (urea, sucrose) of tracers in anesthetized rats. Samples of cochlear EL, PL of scala vestibuli (PLV), PL of scala tympani (PLT), and cisternal CSF were obtained. The data showed slow entry of tracers in PLV, PLT, and CSF as follows: Na greater than urea greater than mannitol approximately sucrose; slower entry of mannitol and sucrose in PLT and CSF than in PLV; 1 h delayed peak of radioactivity in PLV compared with the immediate peaks in PLT and CSF after CSF injection, and the value of PLV peak was 13% that in CSF; extremely slow entry of nonelectrolytes in EL. These results indicate that PLV originates mainly from plasma across a blood-perilymph barrier that restricts the entry of small hydrophilic solutes. The blood-perilymph barrier is most likely composed of an endothelial barrier associated with an epithelial secretion. The latter could be located at the vasculo-epithelial zone of the spiral limbus.
Potassium transport in cortical collecting tubules from mineralocorticoid-treated rat
Authors: Schafer J. A. , Troutman S. L.
Published: December 2017

Unidirectional fluxes of 86Rb+ were used to examine the stimulation of K+ secretion produced by arginine vasopressin (ADH) in isolated perfused cortical collecting tubules from rats treated with desoxycorticosterone. ADH at 100 microU/ml in the bathing solution increased the bath-to-lumen flux (Jb----l; pmol X min-1 X mm-1) from 16.9 +/- 2.3 to 43.2 +/- 4.6 (n = 16). The lumen-to-bath flux (Jl----b) fell from 3.2 +/- 0.7 to 1.3 +/- 0.4 with ADH due to hyperpolarization of the transepithelial voltage from -12.6 +/- 1.3 to -39.3 +/- 2.0 mV, but the calculated Rb+ permeability was unaltered at 0.20-0.26 micron/s. Although 2 mM lumen Ba2+ inhibited Jb----l by 55 +/- 6%, the flux ratio (Jb----l/Jl----b) of 28 +/- 8 was larger than predicted for passive exchange. In the absence of ADH 2 mM Ba2+ reduced Jb----l to the level predicted for passive movement, but addition of ADH with Ba2+ still present increased Jb----l by an amount identical to that observed without Ba2+, although the absolute Jb----l was less. Simultaneous addition of 2 mM luminal and 4 mM bath Ba2+ also inhibited Jl----b for 22Na+ but not to passive levels. These results indicate either that the concentrations of Ba2+ used were insufficient to block K+ conductances completely or that K+/Rb+ secretion can occur through a Ba2+-insensitive pathway.
EGF-induced mitogenesis in proximal tubular cells: potentiation by angiotensin II
Authors: Norman J. , Badie-Dezfooly B. , Nord E. P. , Kurtz I. , Schlosser J. , Chaudhari A. , Fine L. G.
Published: December 2017

The mitogenic effect of epidermal growth factor (EGF) and the characteristics of EGF binding were studied on primary cultures of rabbit proximal tubular cells. EGF was found to be a potent mitogen and stimulated DNA synthesis 18-fold above the level observed in quiescent cells. Using 125I-EGF as a ligand, two classes of specific EGF receptors were identified on the proximal tubular cell in culture, i.e., a high-affinity receptor with a dissociation constant (Kd) of 0.3 nM and maximal binding (Bmax) of 1.7 X 10(4) receptors/cell and a low-affinity receptor with a Kd of 1.9 nM and Bmax of 5.3 X 10(4) receptors/cell. Because angiotensin II (ANG II) appeared to possess many properties common to growth factors, we also examined the interaction of ANG II and EGF on these cells. ANG II was not mitogenic, but it potentiated the mitogenic effect of EGF with a maximal effect at 10(-9) M. The dose-response curve of EGF-induced mitogenesis was shifted to the left in the presence of 10(-9) M ANG II, decreasing the approximate half-maximal stimulatory concentration from 3 X 10(-8) to 5 X 10(-9) M. ANG II also stimulated prostaglandin E2 (PGE2) release, but inhibition of basal and ANG II-stimulated PGE2 synthesis had no effect on mitogenesis. ANG II had no effect on the binding of EGF to the high-affinity receptor from 1 to 20 h and did not alter receptor downregulation. ANG II (10(-9) M) had no effect on cell protein content, RNA and protein synthesis, Na+-H+ antiport, and intracellular free Ca2+ concentration. Higher concentrations of ANG II (5 X 10(-8) to 5 X 10(-6) M) led to a rapid and transient dose-dependent rise in cytosolic free Ca2+ concentration. These studies demonstrate that ANG II potentiates EGF-induced mitogenesis at one or more postreceptor steps that may include small changes in cytosolic Ca2+ concentration.
Effect of protein-restricted diet on renal response to a meat meal in humans
Authors: Viberti G. , Bognetti E. , Wiseman M. J. , Dodds R. , Gross J. L. , Keen H.
Published: December 2017

To study the influence of preceding dietary protein intake on the renal response to a protein meal we examined renal hemodynamic and excretory responses to a meat meal in six normal human subjects either taking their normal-protein diet (NPD, 75 +/- 5 g/day) or after 3 wk of a low-protein diet (LPD, 43 +/- 3 g/day; P less than 0.005). Glomerular filtration rate (GFR) was lower on LPD than on NPD (107 +/- 7 vs. 124 +/- 5 ml X min-1 X 1.73 M-2, respectively; P less than 0.01), as was renal plasma flow (RPF) (NPD, 666 +/- 44; LPD, 605 +/- 43 ml X min-1 X 1.73 M-2; P less than 0.05). Filtration fraction (FF) was not different (NPD, 0.19 +/- 0.01; LPD, 0.18 +/- 0.01). Urinary excretion of albumin was also lower after LPD than NPD (2.1 +/- 0.5 vs. 4.2 +/- 0.8 micrograms/min; P less than 0.05). After an 80-g protein meat meal, GFR rose to a ceiling significantly higher on NPD than on LPD (132 +/- 4.8 vs. 120 +/- 5.2 ml X min-1 X 1.73 M-2; P less than 0.02), even though the percent changes were greater on LPD than on NPD (12.7 +/- 3.3 vs. 6.6 +/- 1.5%, respectively; P less than 0.05). There was a rise in RPF that was entirely attributable to a fall in renal vascular resistance, and FF did not change. On both diets, oral protein loading produced a 200-300% increase in the urinary excretion and fractional clearance of albumin and IgG, but failed to alter that of beta 2-microglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic hypercapnia enhances Vmax of Na-H antiporter of renal brush-border membranes
Authors: Talor Z. , Yang W. C. , Shuffield J. , Sack E. , Arruda J. A.
Published: December 2017

Chronic hypercapnia is associated with increased proximal HCO3 reabsorption that is thought to be mediated by a Na-H antiporter. We hypothesized that chronic hypercapnia would be associated either with increased Vmax or with decreased Km of the Na-H antiporter. To test this hypothesis we made rabbits hypercapnic for 48 h by exposure to 10% CO2. In both control and hypercapnic animals, cortical luminal membranes were enriched over the homogenate 16-fold in alkaline phosphatase and 10-fold in maltase activity. The kinetic activity of the Na-H antiporter was measured by the dissipation of the quenching of acridine orange by addition of different Na concentrations. Chronic hypercapnic rabbits had significantly higher Vmax of the Na-H antiporter of luminal membranes than controls (593 +/- 81 vs. 252 +/- 40 arbitrary fluorescence units X min-1 X 300 micrograms protein-1, P less than 0.01). The Km, however, was not different between control and hypercapnic rabbits. 22Na uptake in presence of an outwardly directed pH gradient was significantly higher in vesicles from hypercapnic rabbits than controls. Amiloride inhibited the Na-H antiporter (as assessed by acridine orange quenching or 22Na uptake) to the same degree in membranes from both control and hypercapnic rabbits, suggesting that the increase in Vmax is mediated by the electroneutral component of the Na-H antiporter. In addition, under voltage clamp conditions by K and valinomycin the Vmax was still increased in membranes from hypercapnic animals, again suggesting that the increase in Vmax is mediated by the electroneutral component of the Na-H antiporter. The uptake of D-[3H]glucose by luminal membranes was not different between control and hypercapnic rabbits, indicating a specific enhancement of the Na-H antiporter. Acute hypercapnia (4 h) failed to increase the Vmax of the Na-H antiporter despite comparable increase in PCO2. Thus chronic hypercapnia, but not acute hypercapnia, induces a selective and specific increase in the Vmax of Na-H antiporter, and this may mediate the adaptation to chronic hypercapnia.(ABSTRACT TRUNCATED AT 250 WORDS)
Characterization of K-ATPase activity in distal nephron: stimulation by potassium depletion
Authors: Doucet A. , Marsy S.
Published: December 2017

Intercalated cells of the distal segments of the mammalian nephron are able to reabsorb K through an active mechanism, particularly during K depletion. However, the molecular basis of this transport is unknown. Therefore, we attempted to determine whether a K-ATPase similar to K-H-ATPase described in gastric mucosa and colon might be present in segments of the distal nephron and thereby account for active K reabsorption. K-stimulated ATPase activity was detected in microdissected segments of rabbit nephron: its activity was proportional to the density of intercalated cells, since it was highest in the connecting tubule, intermediate in the cortical collecting tubule, lowest in the outer medullary collecting tubule, and was not detectable in all other nephron segments. K-ATPase had a high affinity for K (Km approximately equal to 0.2-0.4 mM), was inhibited by vanadate and omeprazole, and was insensitive to ouabain, indicating that it is different from Na+-K+-ATPase but similar to K-H-ATPase. In the rat kidney, K-ATPase was also detected in the collecting tubule and its activity was markedly increased (+100-200%) following K depletion. This stimulation occurred before morphological alterations and might therefore be a primary event responsible for K conservation during K depletion. In summary, these results demonstrate the presence of a vanadate-sensitive, ouabain-insensitive K-ATPase activity in distal nephron segments of mammalian tubules. It is suggested that K-ATPase activity originates in intercalated cells where it might account, at least in part, for K reabsorption.
Effect of V2-receptor-mediated changes on inner medullary blood flow induced by AVP
Authors: Kiberd B. , Robertson C. R. , Larson T. , Jamison R. L.
Published: December 2017

We have previously shown that arginine vasopressin (AVP) in physiological amounts reduces inner medullary blood flow and that the mechanism of this decrease is at least in part mediated by the vasopressor (V1-receptor) action of AVP. To determine whether the antidiuretic action of AVP (V2-receptor) also contributes to the reduction in inner medullary blood flow, we determined capillary blood flow (QVR) in individual descending vasa recta (DVR) and ascending vasa recta (AVR) using fluorescence videomicroscopy in the exposed renal papilla of the anesthetized rat. Three groups of chronically water-diuretic rats were studied in three consecutive periods: control (period 1), experimental (period 2), and recovery (period 3). Group I rats (designated the AVP group) received AVP, 45 ng X h-1 X kg body wt-1; group II (AVP + V2-inhibitor), AVP plus its specific antidiuretic antagonist d(CH2)5[D-Ile2,Thr4]AVP; and group III (V2-inhibitor), the antagonist alone, respectively, in the experimental period 2. Only group I rats concentrated their urine, urine osmolality (Uosmol) = 499 +/- 48 mosmol/kgH2O, whereas urine remained hypotonic throughout in groups II and III. In group I, QVR in DVR and AVR decreased in period 2; but in groups II and III, QVR tended to increase. These results suggest that the AVP-induced decrease in papillary vasa recta blood flow is in part mediated by its antidiuretic V2-receptor as well as by its vasopressor (V1-receptor). They also suggest that the rate of urinary flow in the medullary collecting ducts is a determinant of inner medullary blood flow.
Load dependency of sodium chloride reabsorption by medullary collecting duct in rat
Authors: Cupples W. A. , Sonnenberg H.
Published: December 2017

During antidiuresis, the medullary collecting duct (MCD) reabsorbs sodium in load-dependent fashion. However, attempts to characterize reabsorption when sodium delivery to the MCD is elevated have not led to clear results, largely due to interfering effects of the strategies employed to raise delivery. In the present study, microcatheterization was performed in rats undergoing water diuresis induced solely by infusion of 2.5% dextrose in water, and in rats where solute delivery to the MCD was markedly elevated by the combination of water diuresis with acute potassium chloride loading. The results show that delivery of sodium was elevated by the experimental maneuvers, averaging 7.01+/- 0.83 mumol . min-1 . g kidney wt-1 compared with a normal antidiuretic value in the literature of 3.50+/- 0.40 mumol . min-1 . g-1. Sodium and chloride reabsorptions were increased proportionally, indicating that the MCD has a large capacity to transport sodium chloride. Normalized sodium reabsorption remained high, varying in different series between 80+/- 10 and 96+/- 1% of the delivered load. Thus the MCD reabsorbed an average of 6.37+/- 0.70 mumol . min-1 . g-1 of sodium while sodium excretion was 0.52+/- 0.11 mumol . min-1 . g-1. The results emphasize the importance of MCD sodium chloride reabsorption for determination of final urinary salt excretion, and thus for regulation of body salt balance.
O2 metabolites cause reperfusion injury after short but not prolonged renal ischemia
Authors: Linas S. L. , Whittenburg D. , Repine J. E.
Published: December 2017

Toxic O2 metabolites have been postulated to contribute to renal ischemia-reperfusion injury, but their biochemical assessment and contribution as a function of the duration of ischemia is unclear. To address this issue we measured renal function and renal cortical glutathione levels following 20, 30, or 45 min of ischemia in situ and then 60 min of reperfusion by the isolated kidney technique. Increasing durations of ischemia were associated with progressive decreases in perfusion flow rate, glomerular filtration rate, tubular Na reabsorption, and renal cortical glutathione following reperfusion. However, reperfusion following simultaneous addition of the permeable O2 metabolite scavenger dimethylthiourea (DMTU; but not urea) prevented glutathione consumption and attenuated reperfusion-induced injury after 20 and 30 min of ischemia. In contrast, reperfusion with DMTU prevented glutathione consumption but did not improve renal function after 45 min of ischemia. Similarly, reperfusion with dimethyl sulfoxide also attenuated renal injury after 20 and 30 min, but not after 45 min of ischemia. Thus reperfusion of kidneys made ischemic for 20 or 30 min is associated with decreases in tissue glutathione and renal function that were both inhibitable by addition of O2 metabolite scavengers during reperfusion. In contrast, addition of O2 metabolite scavengers during reperfusion of kidneys previously made ischemic for 45 min prevented decreases in glutathione but did not improve renal function. We conclude that O2 metabolites formed during reperfusion contribute to functional impairment in kidneys made ischemic for short durations up to 30 min) but that after prolonged ischemia (greater than 30 min) injury is primarily mediated by non-O2 metabolite-dependent cellular events.
Effects of adrenalectomy on CCD: evidence for differential response of two cell types
Authors: Muto S. , Giebisch G. , Sansom S.
Published: December 2017

Electrophysiological and chemical methods were used to determine the Na and K transport properties of the isolated cortical collecting duct (CCD) of control and adrenalectomized (ADX) rabbits. Net fluxes of Na (JNa) and K (-JK) in controls were 5.7 and 3.2 pmol . mm-1 . min-1 and in ADX were 1.0 and 0.7 pmol . mm-1 . min-1, respectively, similar to electrically determined rates. In separate experiments, blind impalement of cells from adrenal intact (group 1), ADX (group 2), and ADX rabbits treated with deoxycorticosterone (group 3) allowed identification of two distinct cell types, majority cells (MA) and minority cells (MI). In all groups, MA were distinguished from MI by a relatively high basolateral membrane potential (-Vb), low apical membrane fractional resistance (FRa), and presence of apical and basolateral membrane K conductances. Vb of MA (-82.4 mV) was significantly hyperpolarized in groups 1 and 3 combined, when compared with group 2 (-66.4 mV). However, there was no significant difference between Vb of MI in group 2 (-38.9 mV) and Vb of MI in groups 1 and 3 (-36.2 mV). In MA of group 1 equivalent circuit values of apical membrane Na and K conductances (GNaa, GKa) and maximum pump current (Ipmax) were 0.84 and 6.72 mS/cm2 and 46.7 microA/cm2, respectively. These values in group 2 were significantly lower (0.28 and 1.52 mS/cm2 and 8.7 microA/cm2, respectively). It is concluded that two cell types can be distinguished electrically in the CCD. MA have properties consistent with principal cells and MI have properties consistent with intercalated cells. ADX causes a decrease in GNaa, GKa, and Ipmax of PC that results in proportionate decreases in INaa and IKa.