bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of parathyroid hormone on urinary acidification
Authors: Bichara M. , Mercier O. , Paillard M. , Leviel F.
Published: December 2017

Recollection micropuncture experiments were carried out in plasma-replete euvolemic thyroparathyroidectomized rats to examine the effects of a purified bovine parathyroid hormone (PTH) infusion on urinary acidification. After a 60-min equilibration period, PTH administration had the following effects: reabsorption in the proximal convoluted tubule was inhibited 13% for total CO2, 31% for chloride, and 28% for water; early distal delivery, however, remained unchanged for bicarbonate, chloride, and water principally as a result of stimulation of bicarbonate and chloride absorption in Henle's loop; the urinary bicarbonate and chloride excretion rates did not vary significantly, but the urinary pH decreased from 6.78 +/- 0.11 to 6.39 +/- 0.07 and titratable acid and ammonium excretion increased from 63 +/- 18 to 405 +/- 45 and from 422 +/- 30 to 647 +/- 44 nmol X min-1 X g kidney wt-1, respectively. In another group of rats, the bicarbonate urinary excretion rate increased more than twofold during the first 60 min of PTH infusion and then returned to control levels as was observed in the other groups; the transient increase in bicarbonaturia was attributable to a PTH-induced transient augmentation in glomerular filtration rate and bicarbonate filtered load. Finally, no change was noted in micropuncture or whole-kidney data in time-control rats. We conclude that PTH only transiently enhances the bicarbonate filtered load and urinary excretion rate during the first 60 min of administration secondary to an early hemodynamic action but that the steady effect is to stimulate urinary acidification and net acid excretion, which could generate metabolic alkalosis; and that the inhibition of the proximal bicarbonate and chloride reabsorption induced by PTH is counterbalanced by stimulation of reabsorption in Henle's loop.
Hypercalciuria of mineralocorticoid escape: clearance and micropuncture studies in the rat
Authors: Gehr M. K. , Goldberg M.
Published: December 2017

Chronic mineralocorticoid excess results in the predicted retention of salt and water followed by a period of escape from sodium retention and hypercalciuria. We studied a rat model during mineralocorticoid escape (ME) with clearance and micropuncture studies to ascertain the nephron site and possible role of parathyroid hormone. Rats during ME were hypercalciuric compared with a matched saline group. Clearance studies revealed a marked difference in the calcium-to-sodium fractional excretion ratio (FECa/FENa) between saline-expanded and mineralocorticoid (desoxycorticosterone acetate, DOCA)-escaped animals (saline-expanded, 0.40 +/- 0.09 vs. DOCA, 1.02 +/- 0.14; P less than 0.01). The addition of either hydrochlorothiazide (HCTZ) or amiloride (AMIL) to the ME animals significantly lowered this ratio from that seen in the intact ME group (DOCA-HCTZ, 0.47 +/- 0.07; DOCA-AMIL, 0.83 +/- 0.14). Neither parathyroidectomy (PTX) nor parathyroid hormone infusions (PTH) in ME animals altered the FECa/FENa from that seen in the intact ME group (DOCA-PTX, 1.15 +/- 0.20; DOCA-PTH, 1.25 +/- 0.18). Segmental micropuncture along the length of superficial nephrons demonstrated no differences in calcium delivery to late proximal, early distal, and late distal sites. However, FECa was markedly increased in ME animals compared with saline controls (saline, 0.48 +/- 0.13% vs. DOCA, 1.62 +/- 0.24%; P less than 0.05). We conclude that the hypercalciuria of ME is independent of PTH and can be significantly reduced by HCTZ or AMIL. Micropuncture and clearance data suggest that the hypercalciuria of ME is mediated in the terminal nephron. The differences in the results when superimposing various factors that influence distal nephron calcium reabsorption on ME may be related to differences in their site(s) of activity on calcium transport.
Exchange of multiple indicators across renal-like epithelia: a modeling study of six physiological regimes
Authors: Lumsden C. J. , Silverman M.
Published: December 2017

Multiple indicator dilution (MID) provides a means of quantifying the unidirectional steady-state fluxes of in vivo tracer movement within organs. In this report a MID model of tracer exchange across renal-like epithelia is developed in mathematical form. Six regimes of epithelial transport function are defined on the basis of the relative sizes of the tracer fluxes. Evidence for the existence of each regime has previously been obtained empirically. These are net secretion, net reabsorption, kinetic sink, antiluminal drive, antiluminal equilibration, and antiluminal trapping. By means of the mathematical model, the indicator dilution properties of the six regimes are compared. The principal similarities and differences among the regimes are documented and related to the physical basis of the transport processes. The findings suggest that over a wide range of physiologically meaningful flux magnitudes the functional regimes can be distinguished via existing empirical methods of MID. The model provides an improved basis for carrying out these distinctions in specific applications.
Specific alpha 1-, alpha 2-, and beta-responses to norepinephrine in pyruvate-perfused rat kidneys
Authors: Baines A. D. , Ho P.
Published: December 2017

We compared the effects of alpha- and beta-adrenergic agonists on vascular resistance, gluconeogenesis (GNG), and electrolyte excretion in pyruvate-perfused rat kidneys. Norepinephrine (NE) (15-60 nM) increased vascular resistance (2-19%) and GNG (42-49%) and decreased fractional excretion of Na (18-34%), Cl (38-48%), and K (13-27%). Prazosin and yohimbine blocked the vasoconstrictor but not the antinatriuretic response. Prazosin revealed an antiphosphaturic and inhibited the gluconeogenic response. Propranolol blocked the effect on Na and Cl (66%) and K excretion (100%). Methoxamine (0.6-1 microM) maximally increased GNG (40-52%) with little effect on vascular resistance (+0-9%) and NaCl excretion (-0-11%). Adding glucose to the perfusate increased methoxamine's effects on electrolyte excretion and vascular resistance. Mercaptopicolinate did not alter methoxamine's effects during pyruvate perfusion. Clonidine (0.1 microM) decreased phosphate excretion without vasoconstriction or antinatriuresis; 0.5-1 microM vasoconstricted and decreased NaCl excretion. Isoproterenol (0.1 microM) vasodilated and decreased Na (25%), Cl (40%), and K excretion (20%). Thus alpha 1- and beta-receptors could account for the effect of NE on GNG and K reabsorption, respectively. Synergism of alpha 1, alpha 2, and beta were required for full antinatriuresis. Glucose increased alpha 1-stimulated vasoconstriction and antinatriuresis. Blocking alpha 1-receptors revealed an alpha 2-like antiphosphaturic response.
Norepinephrine increases Na+-K+-ATPase and solute transport in rabbit proximal tubules
Authors: Beach R. E. , Schwab S. J. , Brazy P. C. , Dennis V. W.
Published: December 2017

We studied the effects of norepinephrine on solute transport and oxidative metabolism in proximal tubules. Norepinephrine (10(-6) M) in the bath stimulated fluid absorption (Jv) by proximal convoluted tubules from 0.76 +/- 0.10 to 1.01 +/- 0.11 nl X mm-1 X min-1 (P less than 0.001). Bicarbonate, chloride, and phosphate transport also increased in proportion to the increases in Jv. Norepinephrine increased ouabain-sensitive oxygen consumption (QO2) in suspensions of cortical tubules by 1.3 nmol X mg protein-1 X min-1 and had no effect on ouabain-insensitive QO2 or mitochondrial respiration. Na+-K+-ATPase activity in basolateral membranes prepared from cortical homogenates incubated with norepinephrine increased from 277.1 +/- 34.9 to 411.1 +/- 38.6 nmol Pi X mg protein-1 X min-1 (P less than 0.005). Norepinephrine also increased Na+-K+-ATPase activity of cortical homogenates by 72% but had no effect on Na+-K+-ATPase if added directly to purified basolateral membranes. These studies show that norepinephrine stimulates solute transport in the proximal tubule by increasing Na+-K+-ATPase activity indirectly through some component or components of the adrenergic receptor system.
Transepithelial ammonia concentration gradients in inner medulla of the rat
Authors: Good D. W. , Caflisch C. R. , DuBose T. D.
Published: December 2017

Transport of NH3 from loops of Henle to medullary collecting ducts has been proposed to play an important role in renal ammonia excretion. To determine whether transepithelial ammonia concentration gradients capable of driving this transport are present in the inner medulla, micropuncture experiments were performed in control rats and in rats with chronic metabolic acidosis. In situ pH and total ammonia concentrations were measured to calculate NH3 concentrations ([NH3]) for base and tip collecting duct, loop of Henle, and vasa recta. In control and acidotic rats, [NH3] in the loop of Henle was significantly greater than [NH3] in the collecting ducts. [NH3] did not differ in loop of Henle and adjacent vasa recta in either group of rats, indicating that NH3 concentration gradients between loop and collecting duct represent NH3 gradients that are present between medullary interstitium and collecting duct. During acidosis, an increase in collecting duct ammonia secretion was associated with an increase in the NH3 concentration difference between loop of Henle and collecting duct but occurred in the absence of a fall in collecting duct pH. The NH3 concentration gradient favoring diffusion of NH3 into the collecting ducts increased during acidosis because [NH3] in the loop of Henle and medullary interstitium increased more than [NH3] in the collecting duct. These findings indicate that transport processes involved in medullary ammonia accumulation play an important role in regulating ammonia secretion into the inner medullary collecting duct in vivo and that a fall in inner medullary collecting duct pH is not necessarily required for ammonia secretion by this segment to increase during chronic metabolic acidosis.
Modulation of renal adrenergic effector mechanisms by calcium entry blockers
Authors: Pelayo J. C.
Published: December 2017

Micropuncture studies in anesthetized Munich-Wistar rats were undertaken to investigate the effects of calcium channel blockade on the glomerular hemodynamic responses to 3-Hz renal nerve stimulation. Stimulation alone increased afferent and efferent arteriolar resistances by 85 and 35%, respectively. Because of these increases both single nephron plasma flow and glomerular capillary hydrostatic pressure difference fell to levels significantly below control, leading to a 26% reduction in single nephron filtration rate (P less than 0.005). These changes, however, were largely attenuated during calcium channel blockade (verapamil, nifedipine). Single nephron filtration rate was only decreased by 14% (P less than 0.05) due to a reduction in single nephron plasma flow. The role of angiotensin II on the residual vasoconstrictive effect of stimulation was also investigated. Pretreatment with an angiotensin-converting enzyme inhibitor (MK 421) of rats infused with verapamil abolished the residual vasoconstriction. The data suggest that calcium influx is an important step for the vasoconstrictive effects of the renal nerves. Additionally, angiotensin II contributes to increased vascular resistance during renal nerve stimulation via a separate, calcium channel mechanism.
Tubule urate and PAH transport: sensitivity and specificity of serum protein inhibition
Authors: Grantham J. J. , Kennedy J. , Cowley B.
Published: December 2017

Macromolecules in rabbit serum inhibit the cellular uptake and transepithelial secretion of [14C]urate and p-[3H]aminohippurate ([3H]PA) in rabbit S2 proximal tubule segments. To understand better the potential role these inhibitors may have in the regulation of renal organic anion excretion, we examined the specificity and relative inhibitory effects on tubule urate and PAH transport of albumin and gamma-globulin, the major inhibitory proteins in rabbit serum. Native rabbit serum markedly inhibited the cellular accumulation of urate and PAH by isolated nonperfused segments [50% inhibition (K0.5) = 0.4 and 0.65 g/dl, respectively]. Urate and PAH transport was also inhibited by bovine serum, human serum, Cohn-fractionated rabbit albumin, and rabbit gamma-globulin, but not by Cohn-fractionated bovine serum albumin. alpha-Lactalbumin and beta-lactoglobulin, derived from milk, also inhibited urate and PAH transport, but to a lesser extent than albumin and gamma-globulin. The transport inhibitory effects of proteins were independent of their binding to urate and PAH. Unidirectional influx and the steady-state intracellular accumulation of urate and PAH in suspensions of proximal tubules were decreased by rabbit serum proteins, suggesting that these inhibitors act on the external face of the cells to diminish the uptake of the organic anions. These studies indicate that the principal plasma proteins (albumin and gamma-globulin) significantly inhibit urate and PAH transporters in the basolateral membranes of S2 proximal tubules. We suggest that circulating plasma proteins that can penetrate the basement membrane of proximal tubules may directly modulate the renal excretion of urate and PAH.
Na+-K+-ATPase activity in medullary thick ascending limb during short-term anoxia
Authors: Chamberlin M. E. , Mandel L. J.
Published: December 2017

Na+-K+-ATPase activity was measured in a suspension of rabbit medullary thick ascending limb tubules under oxygenated and anoxic conditions. Oxygenated, K-depleted tubules rapidly take up added extracellular potassium accompanied by a simultaneous increase in oxygen consumption. The ATP/O2 ratio was 12.5 +/- 0.7, suggesting a tight coupling between oxidative metabolism (6 ATP/O2) and Na+-K+-ATPase activity (2 K/ATP). On reaching anoxia, the tubules released potassium into the medium, but this rate was accelerated by the addition of ouabain, which indicated that the Na+-K+-ATPase was still operative in anoxia. Because 10 min of anoxia led to only a 15.7% decline in potassium content, a new steady state of potassium uptake and leakage must be reached during anoxia. Anaerobic metabolism maintained 73% of cellular ATP during 10 min of anoxia. Exposure of anoxic tubules to iodoacetate produced a 57% decline in ATP levels and a 33% decline in potassium content, which indicated that glycolysis is an important pathway in supplying energy during anaerobiosis.
Cell volume regulation in rabbit proximal straight tubule perfused in vitro
Authors: Kirk K. L. , Schafer J. A. , DiBona D. R.
Published: December 2017

Volume regulation in the perfused proximal nephron of the rabbit was examined quantitatively with a computer-based method for estimating cell volume from differential interference-contrast microscopic images of isolated nephron segments. Following a hyperosmotic challenge (290-390 mosmol), the cells shrank as simple osmometers without a subsequent regulatory volume increase. Conversely, cell swelling induced by a hyposmotic challenge (290-190 mosmol) was completely reversed with a triphasic time course in which a rapid (less than 2 min) initial volume decline was followed by secondary swelling and shrinking phases. A similar regulatory volume decrease was observed following isosmotic cell swelling that was induced by exposure to 290 mosmol, urea-containing solutions. In addition, the cells partially reversed isosmotic swelling that was induced by the luminal replacement of a relatively impermeant cation (i.e., choline) with Na+ and a concomitant increase in luminal solute entry. Our results support two conclusions. First, there exist quantitative differences between the volume regulatory behaviors of perfused and nonperfused proximal tubules, the latter of which exhibit an incomplete and monotonic reversal of hyposmotic cell swelling (M. Dellasega and J. Grantham, Am. J. Physiol. 224: 1288-1294, 1973). Second, the primary physiological role of cell volume regulation in the proximal nephron may be to minimize isosmotic cell swelling associated with acute imbalances in the rates of cell solute entry and exit.
Essential tyrosine residues in transport of organic cations in renal BBMV
Authors: Hsyu P. H. , Giacomini K. M.
Published: December 2017

The effects of tyrosine modifying agents on organic cation transport in brush-border membrane vesicles prepared from rabbit renal cortex were investigated. Treatment of membranes with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and N-acetylimidazole reduced the initial rate of transport of N'-methylnicotinamide (NMN) significantly. The inactivation of NMN transport by NBD-Cl was concentration and time dependent. The maximal transport rate (Tmax) of NMN transport (18.4 +/- 4.3 pmol X s-1 X mg protein-1) in vesicles treated with NBD-Cl (0.15 mM) was reduced to 56% of the Tmax in the control vesicles (32.6 +/- 8.4 pmol X s-1 X mg protein-1, P less than 0.05); whereas the Km was not changed. Treatment with 2-mercaptoethanol reversed the reaction of NBD-Cl with sulfhydryl groups but did not significantly change the transport of NMN in the control or the treated membranes, suggesting that tyrosine but not sulfhydryl residues are involved. The overshoot of NMN uptake in the presence of a proton gradient was 3.38 +/- 0.67 pmol/mg protein in the untreated membranes and was reduced to 2.05 +/- 0.71 pmol/mg protein in the NBD-Cl-treated membranes (P less than 0.05). Studies with the pH-sensitive dye, acridine orange, demonstrated that NBD-Cl-treated vesicles were not leakier with respect to protons, suggesting that NBD-Cl may have specifically affected the organic cation-proton transporter.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of cell Ca and pH on Na channels from rat cortical collecting tubule
Authors: Palmer L. G. , Frindt G.
Published: December 2017

The patch-clamp technique was used to identify individual Na channels in the apical membrane of the rat cortical collecting tubule and to evaluate the effects of cytoplasmic Ca2+ and pH on channel activity. In excised, inside-out patches, the probability of a channels's being open (P0) increased with alkalinization of the solution bathing the cytoplasmic side of the patch. Estimates of P0 were 0.05 at pH 6.4, 0.19 at pH 6.9, and 0.41 at pH 7.4. Varying the free Ca2+ concentration of the solution bathing the cytoplasmic side of the patch had no measurable effect on P0. In cell-attached patches, addition of the Ca2+ ionophore ionomycin to the solution bathing the tubules to a final concentration of either 1 or 10 microM decreased channel activity measured as the mean number of open channels (no. open) = n X P0 where n is the number of channels in the membrane. (no. open) was significantly decreased at 3 min after addition of ionomycin and fell to less than 10% of control values after 10 min incubation. There was no fall in (no. open) either in time controls or in tubules exposed to ionomycin in the presence of low bath Ca2+ concentrations [no added Ca2+ with 1 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA)]. The results suggest that cytoplasmic pH can directly influence channel activity. Cytoplasmic Ca2+ does not interact directly with the channels, but increased cytoplasmic Ca2+ produces a fall in channel activity through an indirect process.
Renal substrate utilization in normal and acidotic rats
Authors: Goldstein L.
Published: December 2017

Renal arteriovenous (A-V) concentration differences of the major potential respiratory substrates were measured in whole blood of control, NH4Cl-acidotic and diabetic ketoacidotic (DKA) rats. Net renal substrate extractions were calculated from A-V differences and renal blood flows. In fed control rats lactate accounted for 78% of the total substrate extracted. Small amounts (10-12%) of citrate and the ketone bodies 3-hydroxybutyrate and acetoacetate were also extracted. There was no significant extraction of either free fatty acids, glucose, glutamine, or pyruvate. In NH4Cl-acidotic rats lactate extraction was lower (40%) than in controls, but glutamine extraction increased (28%). The amount of extra glutamine extracted approximated the fall in lactate extraction. In DKA rats, ketone bodies accounted for the major portion of the extracted substrates (56%) but a significant part of the net extraction was due to urinary excretion of these compounds. Glutamine extraction represented 23% of the total. Lactate extraction was low (14%) in DKA rats, probably as a result of the low arterial lactate concentration. In vitro studies done on renal cortical slices suggest that each of the three major substrates extracted by the kidneys of normal, NH4Cl, and DKA rats could serve as major respiratory fuels.
Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct
Authors: Star Robert A. , Burg Maurice B. , Knepper Mark A.
Published: December 2017

Pages F1148–F1157: Robert A. Star, Maurice B. Burg, and Mark A. Knepper. We regret that an error was made in the title of this article. The correct title and the article are reprinted here.
Production and degradation of calcitriol in renal failure rats
Authors: Hsu C. H. , Patel S. , Young E. W. , Simpson R. U.
Published: December 2017

We studied the metabolism of calcitriol in renal failure achieved by nephrectomy in three groups of rats. Group 1 (n = 7) had sham operation of nephrectomy. Group 2 (n = 8) had unilateral nephrectomy. Group 3 (n = 7) had 5/6 nephrectomy. Metabolic clearance rate (MCR) and production rate (PR) of calcitriol were studied 3 wk after the surgery. Serum creatinine concentrations were increased after nephrectomy for groups 2 and 3. Endogenous plasma levels of calcitriol were not different between the rats with renal failure and the controls. MCR of calcitriol were decreased in renal failure rats compared with controls (group 1, 0.24 +/- 0.01; group 2, 0.20 +/- 0.01, P less than 0.01; group 3, 0.16 +/- 0.01 ml.min-1.kg-1, P less than 0.001). The MCR of calcitriol was correlated with the endogenous creatinine clearance by linear regression analysis (r = 0.72, P less than 0.001). The PR of calcitriol were also decreased in renal failure; however, the decreases were much less than the amount of renal tissue removed. We concluded that production of calcitriol is decreased in the remnant kidney. The decreased synthesis is associated with decreased degradation of calcitriol resulting in normal concentrations of calcitriol in mild to moderately severe renal failure.
Adrenal medullary regulation of rat renal cortical adrenergic receptors
Authors: Sundaresan P. R. , Guarnaccia M. M. , Izzo J. L.
Published: December 2017

The role of the adrenal medulla in the regulation of renal cortical adrenergic receptors was investigated in renal cortical particulate fractions from control rats and rats 6 wk after adrenal demedullation. The specific binding of [3H]prazosin, [3H]rauwolscine, and [125I]iodocyanopindolol were used to quantitate alpha 1-, alpha 2-, and beta-adrenergic receptors, respectively. Adrenal demedullation increased the concentration of all three groups of renal adrenergic receptors; maximal number of binding sites (Bmax, per milligram membrane protein) for alpha 1-, and alpha 2-, and beta-adrenergic receptors were increased by 22, 18.5, and 25%, respectively (P less than 0.05 for each). No differences were found in the equilibrium dissociation constants (KD) for any of the radioligands. Plasma corticosterone and plasma and renal norepinephrine levels were unchanged, whereas plasma epinephrine was decreased 72% by adrenal demedullation (P less than 0.01); renal cortical epinephrine was not detectable in control or demedullated animals. Our results suggest that, in the physiological state, the adrenal medulla modulates the number of renal cortical adrenergic receptors, presumably through the actions of a circulating factor such as epinephrine.
Flow-dependent potassium secretion by rabbit cortical collecting tubule in vitro
Authors: Engbretson B. G. , Stoner L. C.
Published: December 2017

Cortical collecting tubules (CCT) dissected from rabbits fed a diet designed to stimulate potassium transport secreted potassium in direct proportion to the flow rate in the range of 0.4-3 nl/min (r = 0.79). This relationship was also evident in tubules from rabbits maintained on standard laboratory chow (r = 0.80). The slope of the line relating the two parameters was almost six times greater in tubules from animals fed the special diet. When the range of flow rates was expanded, potassium secretion in nine CCTs appeared to peak at 5-6 nl/min and then failed to increase despite further elevation of flow to nearly 15 nl/min. We investigated the effects of the electrical and chemical gradients on flow-dependent potassium secretion. Because transepithelial voltage was unaffected by changes in axial flow, we conclude that the flow-dependent fraction of potassium secretion is not explained by the electrical gradient. To evaluate the role of luminal potassium concentration on flow-dependent potassium secretion, 11 CCTs were perfused with both 5 and 50 mM potassium solutions at two flow rates (approximately 1.5 and 4.0 nl/min). Increases in both potassium secretion (15.6 +/- 3.9 peq.mm-1.min-1) and sodium reabsorption (11.9 +/- 5.2 peq.mm-1.min-1) were evident in the tubules perfused with 5 mM potassium. Potassium secretion was not reduced by 50 mM luminal potassium at the low flow rate when the largest chemical gradients opposing net secretion were generated. When 50 mM potassium was present in the lumen, increasing flow did not stimulate potassium secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Na+-H+ exchanger in proximal cells isolated from rabbit kidney. I. Functional characteristics
Authors: Bidet M. , Tauc M. , Merot J. , Vandewalle A. , Poujeol P.
Published: December 2017

The purpose of this study was to investigate the characteristics of the Na+-H+ exchange in isolated proximal cells from rabbit kidney cortex. The cells were prepared by mechanical dissociation and sequential passages through nylon meshes. The intracellular pH (pHi) was measured in a bicarbonate-free medium [extracellular pH (pHe) = 7.30], using the fluorescent dye 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). Resting pHi was 7.13 +/- 0.04 (n = 11) at 20-22 degrees C. Cells were acid loaded with nigericin in choline solution and H+ efflux, induced by extracellular Na+ (Nae), was calculated using a buffering power of 23.6 +/- 0.6 mmol.1-1.pH unit-1 (n = 19) estimated by NH4Cl exposure. In isolated proximal cells, the Na+-H+ antiporter had an apparent Km for Nae of 86.7 +/- 1.5 mM (n = 4) and was competitively inhibited by amiloride with a Ki of 33.3 +/- 6.4 X 10(-6) M (n = 3). Lowering pHe, inhibited the Na+-H+ exchanger. This inhibition was not purely competitive and the Ki was 40.4 +/- 12.7 nM (n = 3). The Na+-H+ exchange was greatly activated when the cytoplasm was acidified. The intracellular H+ concentration dependence did not follow simple Michaelis-Menten kinetics. Of the different cations tested on pHi recovery, such as Li+, choline+, K+, and tetramethylammonium, only Li+ induced an alkalinization of acidified cells similar to that of Na+. 22Na influx measurements indicated that cellular depletion of Na+ stimulated Na+-H+ exchange. The results permit the conclusion that the isolation procedures did not impair the main features of the Na+-H+ antiporter, at least as compared with those previously described in renal brush-border membrane vesicles or in other cellular systems. The integrity of the transporter in isolated proximal cells would permit the direct study of its hormonal and metabolic control.
Glomerular and hormonal responses to dietary protein intake in human renal disease
Authors: Rosenberg M. E. , Swanson J. E. , Thomas B. L. , Hostetter T. H.
Published: December 2017

The effects of dietary protein on glomerular and hormonal function were studied in twelve adults with a variety of glomerular diseases. They were randomly assigned, using a crossover design, to two 11-day periods, one on a high-protein diet (2 g.kg-1.day-1) and the other on a low-protein diet (0.55 g.kg-1.day-1). Improvement in glomerular permselectivity on the low-protein diet was manifested by a decreased 24-h urinary excretion of total protein, albumin, and IgG by 33, 40, and 25%, respectively (all P less than 0.02); a fall in the fractional clearance of albumin (10.1 +/- 6.3 X 10(-3) to 5.8 +/- 3.3 X 10(-3)), and IgG (6.9 +/- 5.1 X 10(-3) to 3.5 +/- 2.3 X 10(-3)) (both P less than 0.02); and a decreased fractional clearance of neutral dextrans of molecular radii 48-56 A (P less than 0.05), when measured on the final day of each dietary period. The high-protein diet was accompanied by a higher plasma renin activity (6.9 +/- 1.6 vs. 3.5 +/- 0.8 ng angiotensin I.ml-1.h-1) (P less than 0.02), and increased excretion of prostaglandin E and 6-ketoprostaglandin F1 alpha. We conclude that a low-protein diet rapidly improves the size-selective defect in glomerular permselectivity.
Effects of aortic constriction and renal denervation in DOCA-hypertensive swine
Authors: Zambraski E. J. , Ciccone C. D.
Published: December 2017

The autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR) was examined in normal and deoxycorticosterone acetate (DOCA)-hypertensive Yucatan miniature swine (YMS). Aortic constriction (AC) was used to vary renal perfusion pressure (RPP) from 158 to 90 mmHg for DOCA-YMS and 124 to 50 mmHg for normals. DOCA animals had calculated RBF autoregulatory indexes demonstrating less effective autoregulation compared with controls. Over the pressure range of RBF autoregulation, control animals also autoregulated their GFR, whereas most DOCA animals did not. When renal function in DOCA-YMS was evaluated at the normotensive RPP of 115 mmHg, GFR, urine volume, and sodium excretion were decreased by approximately 60, 70, and 80%, respectively. In DOCA-YMS, after the normalization of RPP to 115 mmHg, renal denervation significantly increased RBF. In DOCA animals the relative decrease in sodium and water excretion in relation to decreased RPP was not altered by renal denervation. In this hypertensive model the excretion of water and sodium are closely linked to RPP. At a normotensive RPP the sodium retention in the DOCA animals may be even further exaggerated by their inability to autoregulate GFR.
Effect of angiotensin II on Ca2+ kinetics and contraction in cultured rat glomerular mesangial cells
Authors: Takeda K. , Meyer-Lehnert H. , Kim J. K. , Schrier R. W.
Published: December 2017

This in vitro study was undertaken to determine the changes in Ca2+ kinetics and cell shape of cultured putative glomerular mesangial cells in the rat in response to angiotensin II (ANG II). Intracellular Ca2+ ([Ca2+]i) was measured using quin 2. ANG II-stimulated Ca2+ efflux was also determined. ANG II induced rapid concentration-dependent increases in [Ca2+]i and Ca2+ efflux. ANG II also induced contraction of mesangial cells as assessed by alterations in cell shape. Even in Ca2+-free medium, ANG II increased [Ca2+]i and Ca2+ efflux, but to a lesser extent. Under this condition, contraction of mesangial cells induced by ANG II was also observed. Readdition of extracellular Ca2+ after the ANG II-induced increase in [Ca2+]i caused a second and slower [Ca2+]i increase. High potassium (50 mM) induced a change of [Ca2+]i, but to a lesser extent compared with the ANG II-induced change. The Ca2+ channel blocker verapamil (5 x 10(-5) M) partially inhibited ANG II-induced Ca2+ influx but totally blocked the increase in [Ca2+]i induced by high potassium. Verapamil did not inhibit ANG II-stimulated Ca2+ efflux or the change in cell shape. Dantrolene (10(-4) M), a blocker of Ca2+ release from endoplasmic reticulum, inhibited ANG II-stimulated Ca2+ efflux and change in cell shape. These results indicate that ANG II rapidly increases [Ca2+]i in cultured rat mesangial cells, in part by mobilizing Ca2+ from dantrolene-sensitive intracellular pools and in part through activation of receptor-operated and voltage-dependent Ca2+ channels. The [Ca2+]i mobilization, however, seems to be the primary modulator of initial glomerular mesangial cell contraction.
Effect of amino acid infusion as an index of renal vasodilatory capacity in pregnant rats
Authors: Baylis C.
Published: December 2017

Experiments were performed in midterm pregnant and virgin Munich-Wistar rats to investigate how the chronically vasodilated kidney of a gravid animal would respond to a further acute vasodilatory stimulus, in the form of a 90-min intravenous infusion of the amino acid glycine (at 0.167 mmol.kg-1.min-1). In young adult midterm pregnant rats studied in the base-line state, glomerular filtration rate (GFR), single-nephron GFR, renal plasma flow (RPF), and glomerular plasma flow were significantly greater (by approximately 30%) than in virgins due to a gestational renal vasodilation. Despite the underlying chronic renal vasodilation of pregnancy, the kidney of the gravid rat displays a marked further renal vasodilation (with consequent further increases in GFR and RPF) in response to acute glycine loading; the percent increase in GFR and RPF was similar to that seen in the relatively vasoconstricted virgin. This ability to further acutely increase the GFR in the pregnant rat was not limited to animals maintained on a normal protein diet but was also seen in older pregnant rats subjected to the additional chronic vasodilatory stimulus of long-term high-protein feeding, although in these older animals the gestational vasodilation was blunted.
Progressive glomerular injury after limited renal infarction in the rat
Authors: Meyer T. W. , Rennke H. G.
Published: December 2017

Wistar Munich rats subjected to partial renal ablation were compared with intact rats. Group 1 rats were subjected to bilateral segmental infarction of 40% of their total renal mass. Group 2 rats underwent uninephrectomy. Group 3 rats underwent sham operation. Micropuncture and morphological studies were performed in each group at 28 wk after operation. In group 1, glomerular capillary pressure was elevated by 7 mmHg and systemic blood pressure was elevated by 31 mmHg despite reduction of nephron number by only 40% and reduction of glomerular filtration rate (GFR) by only 10%. Progressive albuminuria and segmental glomerular sclerosis were associated with elevation of glomerular capillary pressure in this group. In group 2, single-nephron glomerular filtration rate (SNGFR) was higher than in group 1, but systemic and glomerular capillary pressure remained normal. Group 2 rats developed markedly less albuminuria and glomerular sclerosis than group 1 rats despite more pronounced remnant nephron hyperfiltration. These studies support the view that glomerular hypertension is the major hemodynamic derangement contributing to remnant glomerular injury and show that capillary hypertension can initiate remnant glomerular injury even when the majority of the renal mass remains intact.
Intracellular pH in frog skin: effects of Na+, volume, and cAMP
Authors: Civan M. M. , Cragoe E. J. , Peterson-Yantorno K.
Published: December 2017

Single skins were analyzed by 31P-nuclear magnetic resonance (NMR) spectroscopy during alternate perfusion with control and experimental solutions. Intracellular (pHc) and extracellular (pHo) pH were monitored by measuring the spectral frequencies of intracellular Pi and external methylphosphonate, respectively. Base-line pHc was 7.20 +/- 0.02 (SE) when pHo was 6.99 +/- 0.02. A 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS)-inhibitable, HCO3--dependent alkaline shift in pHc can be elicited by replacing external Cl- by gluconate or sulfate. We now report that this effect is observed even in sodium-free media. The substitution of gluconate for external Cl- has also been reported to shrink cell volume. This shrinkage can be minimized by replacing Cl- with gluconate during perfusion with hypotonic, rather than isotonic, media. Conducted in this manner, the anionic substitution produces a much smaller alkaline shift in pHc. Replacement of external NaCl with N-methyl-D-glucamine chloride acidified the cells reversibly by 0.22 +/- 0.02. In the presence of the Na-H antiport blocker 5-(N-methyl-N-isobutyl)amiloride (MIA), restoration of external Na+ did not increase pHc. Separate addition of MIA acidified the cells by 0.18 +/- 0.03. Adenosine 3',5'-cyclic monophosphate (cAMP) also alters pHc. Addition of 1 mM 8(4-chlorophenylthio)cAMP or 100 mU/ml vasopressin acidified the cells by 0.22 +/- 0.03 and by 0.14 +/- 0.04, respectively. The data suggest that frog skin regulates pHc by the parallel operation of Na-H and Na+-independent Cl-HCO3 antiports. Cell volume and cAMP may play regulating roles in this epithelium.
Intracellular chloride activity of rabbit proximal straight tubule perfused in vitro
Authors: Ishibashi K. , Sasaki S. , Yoshiyama N.
Published: December 2017

To examine the cellular mechanism of Cl- transport in the proximal tubule, cell Cl- activity (aiCl) was measured with double-barreled Cl(-)-selective microelectrodes in the rabbit proximal straight tubules (PST) perfused in vitro. When tubules were perfused and bathed with ultrafiltrate-like solution, aiCl (corrected for the interference from undetermined intracellular anions, 4.2 mM) was 17.8 +/- 0.5 mM (n = 90), and this value was 1.3 times higher than that predicted from passive distribution (basolateral membrane potential, Vbl = -51.9 +/- 0.8 mV). Reducing either luminal or bath Cl- indicated that the basolateral membrane plays a more important role as a determinant of aiCl. aiCl reduction rates induced by luminal Cl- removal was inhibited by 75% by 1 mM SITS added to the lumen but was not inhibited by furosemide (0.1 mM). Application of SITS in the lumen in the control condition, however, did not change aiCl appreciably. Reducing the luminal HCO3- from 25 to 5 mM did not significantly change aiCl or Vbl. Replacing luminal Na+ with choline decreased aiCl but these effects were still present when luminal Cl- was absent. We conclude that in the rabbit PST: 1) Cl- is taken up into the cell against the electrochemical gradient, 2) the basolateral membrane plays a more important role in the regulation of aiCl, and 3) luminal Cl- transport is SITS sensitive and Na+ independent.
Effect of feeding on glomerular filtration rate and proteinuria in conscious aging rats
Authors: Corman B. , Chami-Khazraji S. , Schaeverbeke J. , Michel J. B.
Published: December 2017

Food intake increases glomerular filtration and proteinuria in adult rats. That this postprandial hyperfiltration could be age dependent was investigated in 3-, 10-, 20-, and 30-mo-old rats. Glomerular filtration rate and protein excretion were measured in fed or 24 h fasted conscious animals. In the 3-mo-old rats food ingestion increased renal filtration by 45% from 1.17 +/- 0.08 to 1.73 +/- 0.11 ml.min-1.g kidney wt-1 (n = 6). As the animals became older, the differences between fed and fasted periods became smaller: in 30-mo-old rats glomerular filtration rate was 0.85 +/- 0.03 and 1.01 +/- 0.06 ml.min-1.g kidney wt-1 (n = 6) in fasted and fed conditions, respectively. Proteinuria, which was mainly albuminuria, increased slightly with age and was more markedly reduced by acute food restriction in the 30-mo-old than in the 3-mo-old rats. Because the renin-angiotensin system activity decreases with age, its role in postprandial hyperfiltration was assessed by measuring glomerular filtration in 3-mo-old animals whose angiotensin II converting-enzyme activity was chronically inhibited by daily administration of perindopril. In such experimental conditions there was no longer a difference in renal filtration between fed and fasted rats. These data indicate that 1) postprandial increase in glomerular filtration is to some extent related to the renin-angiotensin system activity; 2) short-term reduction of food intake reduces proteinuria even in senescent rats, although the feeding dependence of the glomerular filtration is blunted with age.
Effect of pH on citrate reabsorption in the proximal convoluted tubule
Authors: Brennan S. , Hering-Smith K. , Hamm L. L.
Published: December 2017

Urinary citrate is an important endogenous inhibitor of calcium nephrolithiasis. Systemic acidosis increases renal citrate reabsorption (decreases urinary excretion) and hence is associated with nephrolithiasis; systemic alkali administration increases citrate excretion. We studied the mechanism by which acidosis and alkalosis alter citrate reabsorption in the proximal convoluted tubule, the predominant nephron segment reabsorbing citrate. Tubules were perfused in vitro and citrate reabsorption was measured by use of luminal [14C]citrate. Changes in solution pH were accomplished by changes in bicarbonate concentration with constant PCO2. Decreasing peritubular pH acutely from 7.4 to 7.2 caused an increase in citrate reabsorption. However, the change seen with an acid peritubular pH was abolished by additional buffering of the luminal solution. Increasing peritubular pH from 7.4 to 7.6 resulted in a fall in citrate reabsorption that was not significantly greater than a time-dependent fall in citrate reabsorption in this preparation. The effect of luminal pH on proximal citrate reabsorption was also examined directly. Decreasing perfusate (luminal) pH from 7.4 to 7.2 with constant peritubular pH increased citrate reabsorption. Increasing perfusate pH to 7.6 decreased citrate reabsorption insignificantly (0.1 less than P less than 0.2). These data suggest that luminal pH in the proximal tubule is an important determinant of alterations in citrate reabsorption with acid-base disorders. The effect of luminal pH on citrate reabsorption is probably due to a change in concentration of the transported ionic species, citrate2-.
Tubular site(s) of action of atrial natriuretic peptide in the rat
Authors: Fried T. A. , Osgood R. W. , Stein J. H.
Published: December 2017

With micropuncture techniques, the present study examined the delivery of chloride to the superficial late distal tubule and the base and tip of the papillary collecting duct in rats treated with either Wy 47663, a synthetic analogue of atrial natriuretic peptide (ANP), or vehicle alone. Whole kidney glomerular filtration rate (GFR) and single-nephron glomerular filtration rate were not significantly different between the two groups. Late distal tubule chloride delivery was also not different between ANP- (5.71 +/- 1.15%) and vehicle- (6.28 +/- 1.12%) treated animals. However, fractional delivery to the base of the papillary collecting duct was significantly greater in the ANP-treated rats (14.37 +/- 1.98%) compared with vehicle-treated rats (7.32 +/- 1.47%). Tip papillary collecting duct delivery was also significantly greater in the ANP-treated rats (1.97 +/- 1.96 vs. 3.09 +/- 0.60%). In addition, the percent of chloride delivered that was reabsorbed along the papillary collecting duct was significantly less in the ANP-treated rats. In conclusion, ANP inhibits reabsorption in some tubular segments between the superficial late distal tubule and papillary collecting duct base as well as in the accessible portion of the papillary collecting duct.
Ion concentrations in subcutaneous interstitial fluid: measured versus expected values
Authors: Gilanyi M. , Ikrenyi C. , Fekete J. , Ikrenyi K. , Kovach A. G.
Published: December 2017

Electrolyte concentration values in interstitial fluid samples that have been reported by a number of authors were markedly different from those of a hypothetical ultrafiltrate of plasma. Because no adequate explanation has been provided for the discrepancy, we attempted to study the question 1) by measuring ion and protein concentration in the plasma and in the interstitial fluid samples, and 2) by constructing a theoretical model for ion distribution. Subcutaneous interstitial fluid samples were collected in rats by the implanted capsule and by the liquid paraffin cavity techniques. The samples were analyzed for sodium, potassium, calcium, chloride, total protein, and protein fractions. The ion distribution between vascular and interstitial compartments was found to correspond to the Donnan equilibrium. On theoretical ground it was concluded: the Donnan distribution is valid, if the size of ,free-fluid spaces- is relatively large (r greater than 0.03 micron) compared with the rather short range of electrostatic interactions (approximately 0.8 nm). Due to the relatively small difference in protein concentrations between blood plasma and interstitial fluid and to the short range of electrostatic interactions, the influence of proteins on the distribution of small ions is negligible.
Glomerular atrial natriuretic factor receptors during rehydration: plasma NH2- and COOH-terminal levels
Authors: Gauquelin G. , Thibault G. , Cantin M. , Schiffrin E. L. , Garcia R.
Published: December 2017

Atrial natriuretic factor (ANF) concentration in atria and plasma was investigated in relation to the density and affinity of renal glomerular ANF receptors during water deprivation and rehydration in the rat. Immunoreactive (IR) ANF-(99-126) was lower during water deprivation (4.2 +/- 0.5 fmol/ml) than in normally hydrated animals (10 +/- 1.5 fmol/ml); NH2-terminal IR ANF-(1-98) was also lower in water-deprived rats (75 +/- 2.4 fmol/ml) than in the controls (708 +/- 105 fmol/ml). These decreased plasma COOH- and NH2-terminal ANF concentrations were accompanied by significantly higher hematocrit, serum osmolality, and Na+ values. The renal glomerular ANF receptor population was greater in water-deprived animals than a control animals. After rehydration, IR ANF was elevated within 1 h and reached control values after 6 h. Hematocrit, serum osmolality, and Na+ did not normalize until 48, 6, and 24 h, respectively. The renal glomerular ANF receptor population, which was markedly higher in water-deprived rats, gradually declined after rehydration, so that no difference was observed with the control group 24 h later.
Locally formed dopamine inhibits Na+-K+-ATPase activity in rat renal cortical tubule cells
Authors: Seri I. , Kone B. C. , Gullans S. R. , Aperia A. , Brenner B. M. , Ballermann B. J.
Published: December 2017

Dopamine, generated locally from L-dopa, inhibits Na+-K+-ATPase in permeabilized rat proximal tubules under maximum transport rate conditions for sodium. To determine whether locally formed dopamine inhibits Na+-K+-ATPase activity in intact cortical tubule cells we studied the effect of L-dopa on ouabain-sensitive oxygen consumption rate (QO2) and 86Rb uptake in renal cortical tubule cell suspensions. L-Dopa (10(-4) M) did not affect ouabain-insensitive QO2 or mitochondrial respiration. However, L-dopa inhibited ouabain-sensitive QO2 in a concentration-dependent manner, with half-maximal inhibition (K0.5) of 5 x 10(-7) M and a maximal inhibition of 14.1 +/- 1.5% at 10(-4) M (P less than 0.05). L-Dopa also blunted the nystatin-stimulated QO2 in a concentration-dependent manner, with a K0.5 of 5 x 10(-8) M and a maximal inhibition of 21.8 +/- 1.2% at 10(-5) M (P less than 0.05), indicating that L-dopa directly inhibits Na+-K+-ATPase activity and not sodium entry. Ouabain-sensitive 86Rb uptake was also inhibited by L-dopa (16.0 +/- 2.4%, P less than 0.05). Carbidopa (10(-4) M), an inhibitor of the conversion of L-dopa to dopamine, eliminated the effect of L-dopa on ouabain-sensitive QO2 and 86Rb uptake, indicating that dopamine rather than L-dopa was the active agent. The finding that the L-dopa concentration-response curve was shifted to the left by one order of magnitude in the presence of nystatin suggests that the inhibitory effect is enhanced when the intracellular sodium concentration is increased.(ABSTRACT TRUNCATED AT 250 WORDS)