bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of vasoactive peptides on cytosolic calcium in cultured mesangial cells
Authors: Hassid A. , Pidikiti N. , Gamero D.
Published: December 2017

We have used the “second generation” Ca indicator, fura-2, to measure cytosolic free Ca concentrations in superfused cultures of adherent primary renal mesangial cells. The basal cytosolic free Ca concentration in these cells was found to be 93 +/- 5 nM (n = 35). The Ca ionophore ionomycin (0.1 microM) increased cytosolic Ca levels to a peak value of fourfold above basal, followed by a decline to a steadily maintained concentration of twofold above basal. Two vasoactive peptide hormones, arginine vasopressin and angiotensin II, at maximally effective concentrations, transiently increased cytosolic free Ca levels to peak values of three- and sixfold, respectively, above basal levels. The angiotensin II-evoked increase declined to near basal values before rising again to a value of 1.5- to 2-fold above basal. Cells treated with vasopressin did not have a significant secondary increase of Ca above a small, time-dependent, spontaneous increase. Mesangial cells demonstrated tachyphylaxis to both peptides. However, cross-tachyphylaxis was not observed. Treatment of cells with angiotensin II in ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid-supplemented Ca-deficient medium, or with the Ca channel blockers nifedipine or verapamil, did not eliminate the transient phase of cytosolic Ca metabolism. In contrast, the Ca channel blockers completely inhibited the second sustained Ca response to angiotensin II. These results indicate that angiotensin II and vasopressin mobilize intracellular Ca in cultured adherent mesangial cells. Angiotensin II, but not vasopressin, also appears to increase cytosolic Ca by influx of extracellular Ca through specific channels.
Electrical properties of sodium bicarbonate symport in kidney epithelial cells (BSC-1)
Authors: Jentsch T. J. , Matthes H. , Keller S. K. , Wiederholt M.
Published: December 2017

Intracellular potentials of BSC-1 kidney epithelial cells known to express a Na+-HCO3- symport ranged between -40 and -70 mV, mean value Vm = -55.1 +/- 10.1 mV. Lowering HCO3- at constant partial pressure of CO2 (PCO2) or complete removal of HCO3-/CO2, rapidly depolarized, whereas readding HCO3- hyperpolarized Vm (40 +/- 8 mV/decade HCO3- at constant PCO2). This response was largely reduced by 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (which depolarized Vm to about -20 mV) and in Na+-free medium, but Ba2+ had no effect. In HCO3(-)-Ringer, Na+ removal rapidly depolarized Vm (by 32 +/- 7 mV), and readdition hyperpolarized Vm. This was reduced in HCO3(-)-free medium or by 1 mM DIDS, but not by amiloride (10(-5) and 10(-3) M) or ouabain (10(-4) M). In the absence of HCO3- and/or Na+, steady-state Vm was reduced to -12 +/- 5 mV. Cl- removal had no effect on the responses to Na+ and/or HCO3- and led to a slow steady-state depolarization. Both in the presence and absence of HCO3-, raising pHi (changed by NH4Cl or butyrate) depolarized, whereas lowering pHi hyperpolarized Vm. Lowering pHo in HCO3(-)-free Ringer depolarized Vm (23 +/- 4 mV/decade H+). The slope conductance for K+ is only 6 +/- 2 mV/decade. Thus BSC-1 cells display typical electrical characteristics of Na+-HCO3- symport. In contrast to other systems, the data are compatible with a net electrogenic inward transport of Na+ and HCO3-. There might be an additional H+-(OH-) conductance operating also under nominally bicarbonate-free conditions.
Flow of water between aqueous and vitreous compartments in the rabbit eye
Authors: Maurice D. M.
Published: December 2017

When fluoresceinated dextran (FD) is injected into the vitreous body of the rabbit, it diffuses out of the eye through the anterior chamber so that the ratio of its concentration in the aqueous to that in the vitreous humor remains constant. The rate of loss of the substance from the eye suggests that the vitreous body is stagnant. After penetrating the vitreous body with a 25-gauge needle through the sclera, the FD fluorescence in the aqueous humor is reduced by a factor of three times on the average. This appears to be because the loss of fluid out of the scleral hole sets up a backward seepage of fluid through the anterior vitreous body, which opposes the diffusion of dextran into the anterior chamber. In contrast, making a needle hole has little effect on the level of sulforhodamine B, a more rapidly diffusing molecule, when it has been injected into the vitreous body, and none at all when it has been introduced into the cornea. The changes in the flow across the aqueous-vitreous interface, as well as the changes in aqueous outflow after an experimental intervention to the eye, may be estimated from a comparison of the changes in fluorescence in the anterior chamber of large and small molecular weight compounds injected into the vitreous body.
Calcium modulates vasopressin effect in rabbit cortical collecting tubule
Authors: Dillingham M. A. , Dixon B. S. , Anderson R. J.
Published: December 2017

The calcium ion has been proposed to be an important mediator of the hydroosmotic response to arginine vasopressin (AVP). We examined the effect of reducing basolateral calcium activity on hydraulic conductivity (Lp) in response to AVP in rabbit cortical collecting tubules (CCT) perfused in vitro. Each tubule served as its own control. Reducing bathing fluid calcium from 0.94 mM to 4.6 microM reduced Lp in each tubule (mean decrease from 146 +/- 13 to 106 +/- 7 cm X s-1 X atm X 10(-7), n = 11, P less than 0.025). To determine whether this inhibitory effect was due to a decrease in cellular calcium uptake, we measured the effect of adding 10(-4) M lanthanum to bathing fluid on AVP-stimulated Lp. Lanthanum decreased Lp (from 109 +/- 13 to 80 +/- 10 cm X s-1 X atm X 10(-7), P less than 0.05) in each tubule. To examine the site at which low peritubular calcium activity regulates AVP action, we measured the effect of decreasing bathing fluid calcium on 8-[p-chlorophenylthio]-adenosine 3',5'-cyclic monophosphate (ClPheS-cAMP)-stimulated Lp (n = 5). Decreasing bathing fluid calcium significantly decreases (P less than 0.025) Lp response to ClPheS-cAMP. Since these results suggest that cellular calcium uptake can exert a post-cAMP effect to modulate AVP action, we examined the effect of the calcium ionophore A23187 (10(-7) M) on AVP- and ClPheS-cAMP-stimulated Lp A23187 reversibly potentiates (25-30%, P less than 0.025) the Lp response to both AVP and ClPheS-cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Factors affecting proximal tubular reabsorption during development
Authors: Kaskel F. J. , Kumar A. M. , Lockhart E. A. , Evan A. , Spitzer A.
Published: December 2017

Studies performed in several animal species have demonstrated that glomerulotubular balance is maintained throughout development despite the many changes that occur in the factors known to control it. In an attempt to understand the nature of this phenomenon we quantified the magnitude and described the profile of these changes in guinea pigs. The changes in physical forces were assessed from measurements of hydrostatic and oncotic pressures, whereas those in the permeability characteristics of the proximal tubule epithelium were estimated from permeance to macromolecules of graded radii, histologic measurements of the intercellular channels, and measurements of end-proximal ratio of tubular fluid-to-plasma osmolality (TF/Posm). Between 1 and 50 days of age the net pressure for reabsorption increased from 15.0 to 30.9 mmHg (P less than 0.01, n = 15) with the major change occurring during the first 2-3 wk of postnatal life. The urinary recovery of inulin, sucrose, and creatinine, injected in the early segment of proximal tubules did not vary with age. The urinary recovery of mannitol (MW 180 daltons, Stokes-Einstein radius 4.0 X 10(-10) m) increased from 92% at birth to 100% at 49 days of age (P less than 0.001, n = 24), consistent with a decrease of approximately 0.5 X 10(-10) m in the luminal openings of the paracellular channels. The length of the zonulae occludens and the width of the intercellular channels did not change during this period; however, the length of the channels increased from 5.0 +/- 0.17 to 8.9 +/- 0.48 micron (P less than 0.01, n = 16). These changes should result in an increase in resistance across the intercellular channels. Consistent with this assertion is the observation that the mean TF/Posm of the fluid collected toward the end of the proximal convoluted tubule decreased as a function of age from 1.05 at day 2 to 0.98 at day 80 (P less than 0.001, n = 24). The findings support the hypothesis that during early postnatal life glomerulotubular balance is made possible by a high permeability of the proximal tubule, which compensates for the low net reabsorptive pressure. As the animal matures and the proximal tubule epithelium becomes tighter, for glomerulotubular balance to be maintained, an increase in the number of intercellular channels and in the active transport of sodium need to be postulated.
Calcium-activated phospholipase C associated with canine renal basolateral membranes
Authors: Rogers S. A. , Hammerman M. R.
Published: December 2017

To determine whether calcium-activated phospholipase C effects breakdown of phospholipids present in the basolateral membrane of the renal proximal tubular cell we incubated proximal tubular basolateral membranes isolated from dog kidney in the absence and presence of deoxycholate, and varied free calcium from 0 to 300 microM. Following incubations, lipids were extracted from membranes and separated using thin-layer chromatography. In the absence of deoxycholate, neither phosphatidylinositol nor diglyceride extractable from basolateral membranes changed significantly as calcium was increased. In the presence of deoxycholate, extractable phosphatidylinositol and diglyceride did not change significantly as free calcium was elevated from 0 to 0.03 microM, but phosphatidylinositol decreased and diglyceride increased progressively as 0.03-300 microM free calcium was included in incubations. Most of the increased extractable diglyceride could be accounted for by hydrolysis of phosphatidylinositol as reflected by decreased extractable phosphatidylinositol. Our findings suggest that calcium-activated phospholipase C effects breakdown of phospholipids present in the basolateral portion of the plasma membrane of the renal proximal tubular cell. It is possible that this enzyme plays a role in stimulating protein kinase c at this site.
Two renal alpha 2-adrenergic receptor sites revealed by p-aminoclonidine binding
Authors: Sripanidkulchai B. , Dawson R. , Oparil S. , Wyss J. M.
Published: December 2017

[3H]p-aminoclonidine [3H]PAC, a specific alpha 2-adrenergic agonist, was used to characterize alpha 2-adrenoceptor binding in rat renal membranes. Rosenthal plots demonstrated two binding sites with Kds of approximately 1.7 and 14.2 nM and Bmaxs (maximum binding) of 47.3 and 218.8 fmol/mg protein for the high- and low-affinity sites, respectively. These characteristics were confirmed by estimate of Kd parameters based on association and dissociation experiments. Pseudo-Hill coefficients generated from drug inhibition experiments were all less than unity, suggesting differential binding at two alpha 2-adrenoceptor binding sites. Specific alpha 2-adrenergic agonists exhibited greater binding affinity to both sites than did nonspecific drugs, and all drugs displayed greater affinity for the high- than the low-affinity binding site. Both guanyl nucleotides and sodium chloride inhibited [3H]PAC binding more at the high-affinity than at the low-affinity site. Renal denervation resulted in significant upregulation of receptor density only at the high-affinity sites with no change in receptor affinity at either site, suggesting that a majority of the alpha 2-adrenoceptors in the kidney are postsynaptic. Thus all lines of evidence in this study indicate that two alpha 2-adrenoceptor binding sites exist in the rat kidney.
HCO3 accumulation in proximal tubule: roles of carbonic anhydrase, luminal buffers, and pH
Authors: Bomsztyk K. , Swenson E. R. , Calalb M. B.
Published: December 2017

Most of filtered bicarbonate is reabsorbed in the early proximal tubule, and the high blood-to-lumen HCO3 concentration gradient generated is then maintained in the distal proximal tubule. To determine the factor(s) that prevent reaccumulation of HCO3 in the lumen, surface proximal tubules of the rat kidney were perfused in vivo. All perfusion solutions were similar in ionic composition to late proximal tubule fluid but, instead of HCO3, contained sulfate (SO4) or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES). Bicarbonate concentration ([HCO3]L) was measured by microcalorimetry, while collected fluid PCO2 was maintained in vitro at either renal cortical or atmospheric levels. A new single microelectrode was used to simultaneously measure PCO2 and luminal pH (pHL). With SO4 solution, pHL was 6.84 +/- 0.06, PCO2 was 50.8 +/- 5.0 mmHg, and [HCO3]L was 8.7 +/- 0.9 mM. When 10(-3) M acetazolamide (ATZ) was added to the perfusate, pHL was 7.00 +/- 0.08, PCO2 remained unchanged, [HCO3]L was 12.1 +/- 1.3 mM, and the rate of HCO3 accumulation increased by approximately 50%. When SO4 was replaced with HEPES, pHL increased to 7.18 +/- 0.05, PCO2 was unchanged, [HCO3]L was 16.5 +/- 1.4 mM, and the rate of HCO3 accumulation doubled. Because measured [HCO3]L and that calculated from pHL and PCO2 were approximately the same, the net gain of HCO3 occurred in vivo, a result of either HCO3 backflux and/or intraluminal generation from CO2. By allowing the collected fluid PCO2 to fall to near zero prior to [HCO3]L measurement, we estimate that approximately 50% of the total gain of HCO3 with all solutions was due to backflux.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced urinary kallikrein activity in rats developing spontaneous hypertension
Authors: Ader J. L. , Tran-Van T. , Praddaude F.
Published: December 2017

Urinary kallikrein activity, intake, and excretion of sodium and water were measured in metabolic balance studies on spontaneously hypertensive rats (SHR) of the Okamoto-Aoki strain and normotensive Wistar-Kyoto rats (WKY) on a normal sodium diet from 4 through 15 wk of age. Urinary excretion of active and total kallikrein was significantly lower in SHR at all ages examined and represented a stable percentage of the values in age-matched WKY throughout development, on the average 69.5 and 67.4%, respectively. SHR exhibited a lower urinary excretion of sodium and water than WKY, a higher cumulative sodium balance at all ages studied, and a higher cumulative water balance only at ages 7 and 8 wk. The slopes of the regression lines correlating urinary kallikrein to systolic arterial pressure and to urinary excretion and cumulative balance of sodium and water were always significantly less in SHR than in WKY. The results of the present study indicate that SHR developing hypertension exhibit a precocious and stable abnormality in renal excretion of kallikrein activity.
Cimetidine transport in isolated luminal membrane vesicles from rabbit kidney
Authors: Gisclon L. , Wong F. M. , Giacomini K. M.
Published: December 2017

Experiments were conducted to study the transport of the histamine H2-receptor antagonist, cimetidine, in luminal membrane vesicles prepared from rabbit renal cortex. Cimetidine accumulated in the vesicles with time. Cimetidine uptake was sensitive to changes in vesicle size, suggesting that the compound is transported into an osmotically reactive intravesicular space. Its rate of uptake could be described by both a saturable and a nonsaturable process. The Km was 4.6 +/- 4.0 microM and the Vmax was 6.8 +/- 2.3 pmol X s-1 X mg protein-1 (mean +/- SD, n = 4). N1-methylnicotinamide (NMN), cimetidine, cimetidine sulfoxide, and ranitidine inhibited the uptake of cimetidine. Cimetidine uptake in the presence of an outwardly directed proton gradient was enhanced in vesicles preloaded with a higher concentration of unlabeled cimetidine (2.4 X 10(-4) M). An outwardly directed proton gradient enhanced the uptake of cimetidine to values exceeding its equilibrium accumulation. Uptake stimulated in this way could be inhibited by the cation, NMN, the bases, ranitidine, and cimetidine sulfoxide, and interestingly, by the anion, probenecid. The effect of probenecid did not appear to be due to nonspecific effects on membrane binding, membrane potential, or vesicle size. These data are consistent with data obtained in isolated perfused proximal tubules, demonstrating that probenecid inhibits cimetidine transport. The data in this study suggest that the effect of probenecid on cimetidine transport specifically involves the transporter in the luminal membrane.
Evidence for a high-affinity sodium-dependent D-glucose transport system in the kidney
Authors: Quamme G. A. , Freeman H. J.
Published: December 2017

Renal brush-border membrane D-glucose transport was studied in vesicles prepared from early proximal tubules (outer cortical tissue) and late proximal tubules (outer medullary tissue). Kinetics of sodium-dependent D-glucose uptake, determined with zero trans sodium gradient of 200 mM at 21 degrees C demonstrated a curvilinear Woolf-Augustinsson-Hofstee plot in both cortical and medullary vesicles. Three sodium-dependent systems were discerned in the cortex, possessing Km values of 12.35 +/- 2.2 mM, 520 +/- 39 microM, and 12 +/- 1 microM, respectively. In contrast, only the high-affinity, low-capacity systems were present in the medullary tissue; with respective Km values of 484 +/- 95 microM and 11 +/- 1 microM and mean Vmax values of 2.4 +/- 0.1 and 0.44 +/- 0.08 nmol X mg protein-1 X min-1. The high-affinity systems were more abundant in the medulla than in the cortex. These studies support the notion of multiple transport processes for sodium-dependent D-glucose transport in the pig kidney. Further, they provide evidence for a third, high-affinity system located principally in the medullary tissue, perhaps the late proximal tubule.
Renal effects of cyclooxygenase inhibition in the pregnant rat
Authors: Baylis C.
Published: December 2017

Experiments were performed to investigate the effects of acute cyclooxygenase inhibition on renal hemodynamics in mid and late pregnant rats. In micropuncture studies in the control state, midterm pregnant rats exhibited increased single-nephron glomerular rate (SNGFR) and no change in glomerular or arterial blood pressures. In late pregnancy, SNGFR was no longer significantly elevated, glomerular pressure was similar, and arterial pressure was depressed compared with the virgin. Cyclooxygenase inhibition led to significant increases in single-nephron and whole-kidney filtration and flow in mid and late pregnant rats. This effect was also seen in the virgin control group, and all groups involved a selective renal vasodilation without change in blood pressure. In the absence of anesthesia and surgical stress, cyclooxygenase inhibition had little effect in virgin or pregnant chronically catheterized rats. These studies indicate that the cyclooxygenase-dependent arachidonic acid metabolites are not the agents directly responsible for the gestational rise in the glomerular filtration rate.
Insulin-stimulated protein metabolism in chronic azotemia and exercise
Authors: Davis T. A. , Klahr S. , Karl I. E.
Published: December 2017

To determine whether training reduces the acute catabolic stress of an exercise bout, control and azotemic rats, either exercise trained or untrained, were subjected to a bout of exercise or allowed to rest. Protein turnover was measured immediately following exercise in isolated muscles. Azotemia (no exercise) increased protein degradation; acute exercise (no azotemia) decreased protein synthesis. Protein catabolism was greatest in acutely exercised azotemic rats. Training reduced azotemia-induced and acute exercise-stimulated increase in protein degradation. To determine whether this improvement in protein metabolism by training was due to increased insulin sensitivity, the dose-response to insulin was determined. Resistance of protein synthesis or degradation to insulin was not observed in azotemic rats. Either acute exercise or training increased sensitivities of protein degradation and synthesis to insulin; training also increased responsiveness of protein degradation to insulin. Thus exercise training reduced the elevated muscle protein catabolism due to azotemia and/or acute exercise and enhanced the action of insulin on muscle.
Functional characteristics of peritubular capillary membrane in rat kidney
Authors: Larson M. , Nygren K. , Sjoquist M. , Wolgast M.
Published: December 2017

The permeability characteristics of the peritubular capillary membrane in the rat kidney were investigated on the basis of the transport of hippuran, inulin, myoglobin, horseradish peroxidase, albumin, and gamma-globulin from peritubular capillary blood to renal hilar lymph. Data obtained in a previous investigation on single-nephron plasma flow, filtration fraction, net driving force, and fluid reabsorption along the peritubular capillary were also used. The data were analyzed in a computer-based model taking into account the transport both by diffusion and by convection. The results show that the membrane contains a few large pores through which the plasma proteins leak out into the renal interstitium and a system of several smaller pores responsible for the fluid reabsorption. The mean equivalent radius of the large pores was estimated from the larger molecular probes to be approximately 180 A (range 150-225 A), and the corresponding total pore area over pore length was estimated at 3 X 10(-4) cm (range 6 X 10(-4) to 1 X 10(-4) cm). The small-pore system was analyzed from the transport of hippuran, inulin, and myoglobin and from fluid reabsorption and showed a pore radius of somewhat below 20 A and pore areas over pore length of 50 cm. Here, the fluid reabsorption and the transport of hippuran turned out to be a sensitive marker of the pore area and the transport of inulin and myoglobin of the pore radius.
Basolateral potassium channels in renal proximal tubule
Authors: Sackin H. , Palmer L. G.
Published: December 2017

Potassium (K+) channels in the basolateral membrane of unperfused Necturus proximal tubules were studied in both cell-attached and excised patches, after removal of the tubule basement membrane by manual dissection without collagenase. Two different K+ channels were identified on the basis of their kinetics: a short open-time K+ channel, with a mean open time less than 1 ms, and a long open-time K+ channel with a mean open time greater than 20 ms. The short open-time channel occurred more frequently than the longer channel, especially in excised patches. For inside-out excised patches with Cl- replaced by gluconate, the current-voltage relation of the short open-time K+ channel was linear over +/- 60 mV, with a K+-Na+ selectivity of 12 +/- 2 (n = 12), as calculated from the reversal potential with oppositely directed Na+ and K+ gradients. With K-Ringer in the patch pipette and Na-Ringer in the bath, the conductance of the short open-time channel was 47 +/- 2 pS (n = 15) for cell-attached patches, 26 +/- 2 pS (n = 15) for patches excised (inside out) into Na-Ringer, and 36 +/- 6 pS (n = 3) for excised patches with K-Ringer on both sides. These different conductances can be partially explained by a dependence of single-channel conductance on the K+ concentration on the interior side of the membrane. In experiments with a constant K+ gradient across excised patches, large changes in Na+ at the interior side of the membrane produced no change in single-channel conductance, arguing against a direct block of the K+ channel by Na+. Finally, the activity of the short open-time channel was voltage gated, where the mean number of open channels decreased as a linear function of basolateral membrane depolarization for potentials between -60 and 0 mV. Depolarization from -60 to -40 mV decreased the mean number of open K+ channels by 28 +/- 8% (n = 6).
O2 metabolite-mediated injury in perfused kidneys is reflected by consumption of DMTU and glutathione
Authors: Linas S. L. , Shanley P. F. , White C. W. , Parker N. P. , Repine J. E.
Published: December 2017

The contribution of toxic oxygen (O2) metabolites to ischemic renal injury is unclear because they have not been added directly to the kidney and few ways exist to effectively measure and assess the effect of these highly reactive products in biological systems. Our goal was to determine the effect of hydrogen peroxide (H2O2) or H2O2-derived products on renal function and to determine whether H2O2-mediated renal injury was reflected by consumption of dimethylthiourea (DMTU) (an exogenous O2 metabolic scavenger), depletion of renal cortical total glutathione (an endogenous O2 metabolite scavenger), and/or adenosine triphosphate (ATP). We found that addition of glucose oxidase (GO) or H2O2 to isolated perfused rat kidneys caused injury that was manifested by decreases in glomerular filtration rate, perfusion flow rate, and sodium reabsorption and that was prevented by addition of catalase (CAT) (but not inactivated CAT) or large doses of DMTU (15 mM), but not urea (15 mM). To further ascertain if the protective effect of DMTU was due to reacting with a scavenging H2O2, we conducted parallel experiments in which we measured the consumption of smaller doses of DMTU (1 mM) in kidneys perfused with GO or H2O2. We found that addition of increasing concentrations of H2O2 decreased DMTU concentration. Renal cortical total glutathione and ATP levels were also decreased by addition of GO or H2O2. In contrast to perfusion with GO or H2O2, perfusion with elastase or collagenase also caused renal injury and decreases in ATP but did not decrease DMTU concentration or tissue total glutathione. We conclude that H2O2 or H2O2-derived products are acutely toxic to the kidney and that decreases in perfusate DMTU concentration and tissue total glutathione, but not tissue ATP, may be useful for specifically assessing the presence and/or toxicity of H2O2 in renal and other biological systems.
Degradation and transport of AVP by proximal tubule
Authors: Carone F. A. , Christensen E. I. , Flouret G.
Published: December 2017

High-performance liquid chromatography (HPLC) analysis revealed that [3,4,5-3H-Phe3,Arg8]vasopressin ([3H]AVP) was not degraded by isolated renal brush-border membranes or by a cortical lysosomal fraction in vitro; however, in the presence of 1 mM reduced glutathione, [3H]AVP was degraded by both preparations. Renal cortical homogenates in vitro and luminal peptidases of proximal tubule in vivo degraded [3H]AVP and in both instances yielded phenylalanine, hexapeptide AVP 1-6, heptapeptide AVP 1-7, octapeptide AVP 1-8, and two uncharacterized products X and Y. These data suggest that filtered AVP is reduced in the proximal tubule by a reduced glutathione-dependent transhydrogenase and subsequently cleaved to [3H]Phe by tubular aminopeptidases. Following microinfusion of [3H]AVP into proximal tubules, 15.7% of the label was absorbed. Five and fifteen minutes after infusion of [3H]AVP, sequestration of total label in proximal tubules was 4.5 and 2.1%, respectively, and quantitative electron microscope autoradiography revealed accumulation of grains over apical endocytic vacuoles and lysosomes consistent with endocytic uptake and rapid lysosomal degradation of AVP and/or a large metabolite. Thus, enzymatic cleavage of AVP by luminal and lysosomal peptidases in proximal tubules could involve disulfide bond, C-terminal, and N-terminal loci.
Glomerular hemodynamic adaptations in remnant nephrons: effects of verapamil
Authors: Pelayo J. C. , Harris D. C. , Shanley P. F. , Miller G. J. , Schrier R. W.
Published: December 2017

Chronic verapamil administration has been shown to reduce the renal dysfunction, glomerular sclerosis, and mortality in partially nephrectomized rats; the mechanism is unknown. Therefore, the present micropuncture study examines the effect of verapamil on glomerular hemodynamics of Munich-Wistar rats 4 wk after five-sixths nephrectomy. Whole-kidney function was similar in nephrectomized rats treated with verapamil (Nx-VER) and saline (Nx-SAL), and glomerular filtration rate (GFR) was one-third of control. Both Nx-VER and Nx-SAL rats exhibited a similar degree of glomerular hyperperfusion and hyperfiltration. However, mean glomerular capillary hydrostatic pressure difference (delta P) was lower in Nx-VER than Nx-SAL rats (42.4 +/- 1.2 vs. 47.2 +/- 1.0 mmHg, P less than 0.005) because of an increase in Bowman's space hydrostatic pressure (PBS) in Nx-VER rats (15.5 +/- 0.8 vs. Nx-SAL 11.9 +/- 0.7 mmHg, P less than 0.005). Glomerular ultrafiltration coefficient (LpA) was significantly lower in Nx-SAL (P less than 0.005) than in Nx-VER or control rats. Urinary protein excretion and the magnitude of glomerular sclerosis in Nx-SAL and Nx-VER rats were not different. In conclusion, chronic VER administration normalizes LpA and reduces delta P, by increasing PBS, in Nx rats, alterations that neutralize each other, leading to the constancy of single-nephron GFR.
Angiotensin II-stimulated prostaglandin production by canine renal afferent arterioles
Authors: Hura C. E. , Kunau R. T.
Published: December 2017

Production of prostaglandin E2 (PGE2) and prostacyclin (PGI2) as 6-ketoprostaglandin F1 alpha (PGF1 alpha) in isolated canine superficial and juxtamedullary afferent arterioles was measured in the basal state and after administration of angiotensin II and bradykinin. Individual afferent arterioles were obtained by microdissection, and pooled collections were incubated at 37 degrees C for two consecutive 30-min periods. Prostaglandin content of the incubation media was measured by radioimmunoassay and expressed as picograms prostaglandin per incubation vial per 30-min period. Bradykinin (10(-7) M) produced significant stimulation of both PGE2 and 6-keto-PGF1 alpha production in superficial (PGE2 from 0.44 +/- 0.32 to 5.46 +/- 3.77 pg/period and 6-keto-PGF1 alpha from 6.5 +/- 5.0 to 104.5 +/- 25.5 pg/period) and juxtamedullary afferent arterioles (PGE2 from 0.31 +/- 0.06 to 7.47 +/- 1.55 pg/period and 6-keto-PGF1 alpha from 12.0 +/- 0.01 to 184.4 +/- 14.8 pg/period). Angiotensin II in concentrations of 10(-12) M to 10(-7) M produced no stimulation of prostaglandin production. Angiotensin II (10(-6) M) produced significant stimulation of 6-keto-PGF1 alpha production only in superficial afferent arterioles (from 4.4 +/- 0.8 to 17.3 +/- 3.1 pg/period). Angiotensin II-stimulated 6-keto-PGF1 alpha production was blocked by saralasin (2 X 10(-6) M). A heterogeneous renal vascular response to angiotensin II is demonstrated, since the latter stimulated PGI2 production in superficial afferent arterioles only. PGI2 could potentially antagonize the vasoactive effect of angiotensin II in superficial afferent arterioles.
TEA transport by snake renal tubules: choline effects, countertransport, H+-TEA exchange
Authors: Dantzler W. H. , Brokl O. H.
Published: December 2017

Tetraethylammonium (TEA) transport by isolated perfused snake (Thamnophis spp.) proximal renal tubules was examined for effects of choline and evidence of countertransport of organic cations and H+-TEA exchange. Choline in perfusate significantly inhibited unidirectional lumen-to-bath flux of TEA and accumulation of labeled TEA by tubule cells, and choline in bath significantly inhibited unidirectional bath-to-lumen flux of TEA and accumulation of labeled TEA by tubule cells. These data indicate that choline inhibits transport of TEA into the cells across both the luminal and peritubular membranes and suggest that it may share the TEA transporter. To examine transport at single membranes in intact tubules, we examined the efflux of labeled TEA across the luminal membrane of tubules covered with oil and across the peritubular membrane of tubules with oil-filled lumens. Unlabeled TEA, choline, and low pH in the perfusate stimulated efflux of labeled TEA across the luminal membrane. These data suggest that TEA transport across the luminal membrane can involve countertransport of organic cations and H+-TEA exchange. Unlabeled TEA, choline, and, to a small extent, low pH in the bath stimulated the efflux of labeled TEA across the peritubular membrane. These data suggest that TEA transport across the peritubular membrane can involve countertransport of organic cations and, possibly, H+-TEA exchange. The efflux data across both membranes further support the idea that choline may share the TEA transporter.
Developmental changes in the tubular capacity for phosphate reabsorption in the rat
Authors: Haramati A. , Mulroney S. E. , Webster S. K.
Published: December 2017

The need for young, immature animals to maintain positive phosphate balance for growth is well known. However, whether this process involves changes in the intrinsic capacity of the kidney to reabsorb phosphate is not clear. In the present study, the maximum capacity of phosphate reabsorption [Max RPi/glomerular filtration rate (GFR)] was measured in four groups of rats at different stages of development, from weanling to adulthood (3–4, 5–6, 10–14, and 52 wk of age). Clearance experiments were performed in acutely thyroparathyroidectomized (TPTX) rats in the presence and absence of fixed levels of parathyroid hormone (synthetic PTH-(1–34), 1 U.kg-1.min-1). Max RPi/GFR was determined with progressive infusions of phosphate (0–6 mumol Pi/min) that raised the filtered load of phosphate. Max RPi/GFR in TPTX 3- to 4- and 5- to 6-wk-old rats (5.55 +/- 0.36 and 4.28 +/- 0.18 mumol/ml, respectively) was significantly greater than in the corresponding 52-wk-old rats (3.51 +/- 0.13 mumol/ml, P less than 0.05). PTH decreased the Max RPi/GFR in all age groups. However, the developmental pattern was maintained, with the highest levels present in the youngest rats (2.79 +/- 0.25 mumol/ml, P less than 0.05) compared with the other age groups (1.92 +/- 0.23, 1.35 +/- 0.11, and 1.15 +/- 0.13 mumol/ml for 5- to 6-, 10- to 14-, and 52-wk-old rats, respectively). These results demonstrate that the tubular capacity for phosphate reabsorption per milliliter GFR is enhanced in immature rats and progressively decreases with age. This PTH-independent adaptation in young rats may contribute to the renal retention of phosphate during growth.
Direct vasodilatory action of atrial natriuretic factor on canine glomerular afferent arterioles
Authors: Ohishi K. , Hishida A. , Honda N.
Published: December 2017

Studies were performed to examine whether atrial natriuretic peptide (ANP) has a direct action on glomerular afferent arterioles, and if so, whether the action is mediated by guanosine 5'-cyclic monophosphate (cGMP). A single superficial afferent arteriole was dissected from the canine kidney and perfused with the single glomerular perfusion technique described by Osgood et al. [Am. J. Physiol. 244 (Renal Fluid Electrolyte Physiol. 13): F349–F354, 1983]. Norepinephrine (NE, 1 x 10(-6) M) significantly increased arteriolar resistance, calculated from the perfusion rate and arteriolar pressure. Synthetic human ANP (hANP) provoked afferent arteriolar dilation and attenuated the NE-induced increase in arteriolar resistance with 1 x 10(-10) to 1 x 10(-6) M concentrations. This vasodilatory effect was significantly potentiated by 2-o-propoxyphenyl-8-azapurin-6-one (M&B 22,948, 4 x 10(-12) M), a cGMP phosphodiesterase inhibitor, probably due to a sequential interaction of synergistic drugs. Also, the 1 x 10(-4) M concentration of 8-bromoguanosine 5'-cyclic monophosphate or dibutyryl guanosine, 5'-cyclic monophosphate (DBcGMP) lessened NE-induced arteriolar constriction, but DBcAMP did not. We conclude from these observations that ANP has a direct vasodilatory action on canine glomerular afferent arterioles, and that this ANP-induced vasodilation is mediated by enhanced cGMP synthesis.
Atrial natriuretic factor does not inhibit basal or angiotensin II-stimulated proximal transport
Authors: Liu F. Y. , Cogan M. G.
Published: December 2017

Atrial natriuretic factor (ANF) can functionally overcome the effects of angiotensin II in several tissues. Since ANF and angiotensin II in physiological concentrations have opposite effects on renal sodium excretion, we evaluated whether functional antagonism of the two hormones occurs in the proximal convoluted tubule, as has been recently reported with use of the shrinking split-droplet technique. We used the more conventional technique of in vivo microperfusion to measure the response to systemic ANF (0.5 micrograms.kg-1.min-1) when the endogenous angiotensin II level and proximal transport were normal or when transport was first stimulated by systemic angiotensin II administration (20 ng.kg-1.min-1). In both cases, ANF did not significantly alter bicarbonate, chloride, or water transport in either the early or late proximal convoluted tubule. This inability by ANF to directly affect proximal transport is consonant with the known lack of high-affinity receptors and appropriate second messenger system for ANF in the proximal convoluted tubule.
Evidence suggesting a role for hydroxyl radical in glycerol-induced acute renal failure
Authors: Shah S. V. , Walker P. D.
Published: December 2017

Reactive oxygen metabolites, in particular hydroxyl radical, have been shown to be important mediators of tissue injury in several models of acute renal failure. The aim of the present study was to examine the role of hydroxyl radical in glycerol-induced acute renal failure, a model for myoglobinuric renal injury. Rats injected with glycerol alone (8 mg/kg im following dehydration for 24 h) developed significant renal failure compared with dehydrated controls. Rats treated with glycerol and a hydroxyl radical scavenger, dimethylthiourea (DMTU), had significantly lower blood urea nitrogen (BUN) and creatinine. In contrast, urea, which is chemically similar to DMTU but is not a hydroxyl radical scavenger, provided no protection. In addition, DMTU prevented the glycerol-induced rise in renal cortical malondialdehyde content (a measure of lipid peroxidation that serves as a marker of free radical-mediated tissue injury). A second hydroxyl radical scavenger, sodium benzoate, had a similar protective effect on renal function (as measured by both BUN and creatinine). Because the generation of hydroxyl radical in biological systems requires the presence of a trace metal such as iron, we also examined the effect of the iron chelator, deferoxamine on glycerol-induced renal failure. Deferoxamine was also protective. The interventional agents were also associated with a marked reduction in histological evidence of renal damage. The protective effects of two hydroxyl radical scavengers as well as an iron chelator implicate a role for hydroxyl radical in glycerol-induced acute renal failure.
Effects of plasma amino acid and hormone levels on renal hemodynamics in humans
Authors: Castellino P. , Giordano C. , Perna A. , DeFronzo R. A.
Published: December 2017

The effect of plasma amino acid and hormone (insulin, glucagon, and growth hormone) levels on renal hemodynamics was studied in 18 healthy subjects. The following four protocols were employed: study 1, a balanced amino acid solution was infused for 3 h to increase plasma amino acid concentrations two to three times base line; study 2, the same amino acid solution was infused with somatostatin (SRIF) and infusions of insulin, glucagon, and growth hormone were concomitantly administered to replace the time sequence of increase in peripheral concentrations of these hormones as observed during study 1; study 3, the same amino acid infusion was administered with SRIF plus infusions of insulin, glucagon, and growth hormone to maintain plasma hormone concentrations constant at the basal level; study 4, SRIF was infused with insulin, glucagon, and growth hormone to reproduce the time sequence of increase of these hormones as observed in study 1; amino acids were not infused in this study. During study 1, glomerular filtration rate (GFR) and renal plasma flow (RPF) rose by 19 and 21%, respectively. During study 2 both the time sequence of and magnitude of rise in GFR and in RPF were similar to the changes observed during study 1. In studies 3 and 4 neither RPF nor GFR changed significantly from base line. These results indicate that 1) hyperaminoacidemia stimulates insulin/glucagon/growth hormone secretion and causes a modest rise in GFR and RPF; and 2) if hyperaminoacidemia is created while maintaining basal hormone levels constant or if plasma insulin/glucagon/growth hormone levels are increased while maintaining the plasma amino acid concentration at basal levels, neither RPF nor GFR rise.(ABSTRACT TRUNCATED AT 250 WORDS)
Molecular biology of the renin-angiotensin system
Authors: Dzau V. J. , Burt D. W. , Pratt R. E.
Published: December 2017

This paper reviews the molecular biology of the renin-angiotensin system. The renin gene structure is analyzed in detail, including an examination of the putative regulatory regions. The combined action of these regulatory sequences would result in the complex, tissue-specific expression and regulation observed in vivo. The expression of the tissue renin-angiotensin systems, which may have important physiological functions, is also described. In addition, the pathway of renin biosynthesis and secretion is reviewed. This includes speculation on the fate of circulating prorenin and the physiological role of multiple renin forms and secretory pathways. The molecular approaches described in this paper have greatly advanced our knowledge of the biology of the renin-angiotensin system. Future studies using these and other approaches should provide further insight into this complex system.
Effects of respiratory acidosis on HCO3- transport by rabbit collecting tubules
Authors: McKinney T. D. , Davidson K. K.
Published: December 2017

These studies were performed to determine whether in vitro elevation of bath PCO2 with associated reduction in pH (acute respiratory acidosis) affected bicarbonate transport by isolated perfused rabbit cortical collecting tubules (CCT) and collecting tubules from the outer (OMCTos) and inner (OMCTis) stripes of the outer medulla. When the PCO2 was elevated and pH reduced from approximately 7.4 to 7.0 the rate of total CO2 absorption increased to 252% of that observed at pH 7.4 in CCT, 146% in OMCTos, and 150% in OMCTis. In OMCTis, pretreatment with colchicine inhibited the stimulation of total CO2 absorption associated with respiratory acidosis, whereas lumicolchicine did not. Similar inhibition was observed in the presence of maptam and a low calcium concentration and in the presence of a calmodulin inhibitor. No differences were observed in apical or basolateral membrane morphometry of principal or intercalated cells between control tubules and those subjected to respiratory acidosis. The results indicate that acute respiratory acidosis stimulates acidification by the rabbit distal nephron in vitro through a process(es) that, at least in OMCTis, evidently involves the cell cytoskeleton and changes in cell calcium and calmodulin activities.
Kinetics of a novel cytosolic protein during the onset of renal epithelial cell growth
Authors: Aithal H. N. , Walsh-Reitz M. M. , Kartha S. , Gluck S. L. , Franklin W. A. , Knigge K. M. , Toback F. G.
Published: December 2017

Exposure of monkey kidney epithelial cells (BSC-1 line) to medium with a reduced K concentration (3.2 mM) stimulated growth and transiently activated glyceraldehyde-3-phosphate dehydrogenase (G3PD). The increase in enzyme activity was mediated by a cytosolic modifier protein that was purified using affinity and size-exclusion chromatography, and anion-exchange high-performance liquid chromatography. The apparent molecular mass of the protein was 62 kDa. A monospecific antibody to the protein was prepared from rabbit antiserum and used as an immunoprobe. Immunocytochemical staining and Western blotting revealed that the protein was a normal constituent of the cytosol and that it accumulated in cells exposed to low-K medium. A quantitative enzyme-linked immunosorbent assay showed that the amount of modifier protein increased progressively for up to 2 h in cells exposed to low-K medium, and then returned to the control value, a kinetic profile similar to that observed for G3PD activity. These results indicate that the modifier protein is a constituent of renal epithelial cells and accumulates transiently in the cytosol where it could regulate G3PD activity during the onset of growth induced by the low-K mitogenic signal.
Resistance to blockade by saralasin of effect of ACE inhibitors in conscious sodium-restricted dog
Authors: Zimmerman B. G. , Goering J. L. , Raich P. C.
Published: December 2017

Comparison of the effect of captopril and enalaprilat was made on mean systemic arterial blood pressure (BP), renal blood flow (RBF), and renal vascular resistance (RVR) of conscious sodium-replete and sodium-restricted dogs (plasma renin activity = 6.66 ng angiotensin I.ml-1.h-1). BP was decreased by -8 +/- 2 mmHg and RBF was increased by 34 +/- 12 ml/min with captopril given intravenously and by -5 +/- 2 mmHg and 28 +/- 7 ml/min with enalaprilat in sodium-replete dogs. The respective changes in BP and RBF in sodium-restricted dogs were -29 +/- 2 mmHg and 62 +/- 12 ml/min with captopril and -25 +/- 6 mmHg and 53 +/- 18 ml/min with enalaprilat. Saralasin infused intra-arterially to the kidney significantly blocked the increase in RBF seen after angiotensin-converting enzyme (ACE) inhibition in sodium-replete dogs, and reduced the increase in RBF in sodium-restricted dogs, but the latter effect was not statistically significant. A more moderate increase in plasma renin activity was established in another group of sodium-restricted dogs, and saralasin was administered intravenously instead of intra-arterially. Enalaprilat increased RBF in these dogs in the presence of a saralasin blockade (42 +/- 7 ml/min), and this effect was not significantly changed by prior administration of indomethacin (28 +/- 6 ml/min). The results suggest that blockade of the influence of the renin-angiotensin system and possibly another vasodilator mechanism, such as kinin potentiation, account for the increase in RBF after ACE inhibition in the low-sodium state.
Hypotonic cell volume regulation in mouse medullary thick ascending limb: effects of ADH
Authors: Hebert S. C. , Sun A.
Published: December 2017

Differential interference contrast microscopy was used in combination with standard electrophysiological techniques in the in vitro perfused mouse medullary thick ascending limb of Henle's loop (MAL) to evaluate the cell volume responses of this nephron segment during and following exposure to hypotonic media and to assess the role of antidiuretic hormone (ADH) and net salt absorption on the associated volume regulatory processes. Reductions in extracellular osmolality by 50 mosmol resulted in rapid increases in cell volume of approximately 20% with or without exposure to ADH. Cell volume recovery (volume-regulatory decrease, VRD) was much slower in the presence, than in the absence, of ADH. This hormone-mediated impairment of the VRD response could be overcome by the abolishment of net salt absorption with luminal 10(-4) M furosemide. An inverse linear relationship was observed between the rates of net salt absorption and VRD, indicating a finite ability of this nephron segment to enhance solute exit mechanisms whether induced by increases in transcellular traffic or by hypotonic cell swelling. Finally, returning to the isotonic media resulted in cell shrinkage under all conditions [+/- ADH and +(ADH and furosemide)] consistent with cell solute loss mediating VRD. However, recovery of cell volume back to the initial isotonic control value [post-VRD volume regulatory increase (VRI)] was only observed in ADH-treated tubules and was independent of net salt absorption. The post-VRD VRI response could be abolished by isohydric CO2-HCO3- removal or by addition of 10(-4) M amiloride to the peritubular medium. The latter results suggest that parallel Na+-H+ and Cl- -HCO3- exchangers located in basolateral membranes mediate the post-VRD VRI response.