bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of atrial natriuretic peptide to acute saline loading in essential hypertension
Authors: Mimran A. , Nussberger J. , Ribstein J. , Waeber B. , Brunner H. R.
Published: December 2017

To further investigate the mechanism(s) of the exaggerated natriuretic response of hypertensives to volume expansion (VE; 1,800 ml iv isotonic saline over 3 h), the plasma levels of immunoreactive atrial natriuretic peptide (ANP) were measured in 11 normal subjects (NT) and 12 patients with mild essential hypertension (HT). NT and HT groups were similar with respect to age and basal levels of renin, aldosterone and ANP (34.5 +/- 5.5 in NT and 32.5 +/- 6.3 pg/ml in HT, mean +/- SE). In response to VE, ANP increased to the same extent in both groups (a change of 19.3 +/- 5.2 in NT and of 22.2 +/- 7.1 pg/ml in HT) despite the finding of an exaggerated natriuretic response to VE in essential hypertension (36 +/- 3.5 in NT and 54.9 +/- 6.3 nmol/3 h in HT, P less than 0.02). In addition, the fall in hematocrit and serum protein associated with saline infusion was less marked in HT than NT. The change in ANP induced by VE was inversely correlated with the percent fall in hematocrit and the increment in the fractional excretion of sodium in both groups. These observations suggest that ANPs may participate in the control of the renal response to isotonic VE; however they do not support an unequivocal influence of ANP in the exaggerated natriuretic response to VE of patients with essential hypertension.
To what extent is microtubular network involved in antidiuretic response?
Authors: Valenti G. , Hugon J. S. , Bourguet J.
Published: December 2017

Antimitotic drugs markedly interfere with antidiuretic response, strongly implying that cytoskeleton integrity is essential to this function. This role of the cytoskeleton in controlling the epithelial transport has been seen as a necessary step in the translocation of the water channel containing particle aggregates and in their delivery to the apical membrane. We have now reexamined the exact role of the microtubular network by appropriate time course determinations, by the use of microtubule disruptive agents that lack of the side effects of colchicine, and by trying to visualize the apparent modifications of the microtubular network that accompany water permeability alterations using immunocytochemical techniques. Our results fully confirm that after microtubular network disruption, antidiuretic hormone-induced water permeability variations undergo typical alterations consisting in both a reduction in peak net water flow and a slowing down of its onset. At the same time, the microtubular network disappears in all the epithelial cells. We also show that colchicine-induced inhibition can still be observed in the presence of a prostaglandin synthetase inhibitor and that this inhibition is most likely to occur at a post-adenosine 3',5'-cyclic monophosphate level. These data, as well as results from other series with nocodazole, indicate that the reduction of the net water flow directly results from microtubular network disruption and not from side effects of the disrupting drugs. They also show that the hydrosmotic response is only partially dependent on the microtubular network, which probably has only a guidance role in the translocation of particle aggregates and their exocytotic fusion to the apical membrane.
Renal tubular cells are potential targets for epidermal growth factor
Authors: Goodyer P. R. , Kachra Z. , Bell C. , Rozen R.
Published: December 2017

Epidermal growth factor (EGF) is a potent polypeptide mitogen with various receptor-mediated growth effects on cells from the skin, breast, and gastrointestinal tract. Recent studies indicate that EGF is produced in the kidney and is excreted in the urine, but the biological significance of renal EGF is uncertain. We demonstrate in vitro mitogenicity of EGF for LLC-PK1 cells, a tubular epithelial cell line derived from pig kidney cortex. Furthermore, when subconfluent monolayers of LLC-PK1 cells are exposed to EGF for 24 h, sodium-dependent phosphate transport is stimulated (209-410% of control). These cells possess EGF-specific high-affinity binding sites at their surface (Kd 300-700 pM) but cannot synthesize the growth factor. EGF binding sites are not a peculiarity of the LLC-PK1 cell line, since similar sites are present on MDCK cells (derived from dog kidney distal tubule or collecting duct), primary cultures of mouse proximal tubular cells, and freshly prepared membrane fractions from mouse kidney. Cortical basolateral membranes are highly enriched in EGF binding sites, whereas EGF binding by brush-border membrane fractions is minimal and is compatible with contamination.
Membrane recycling and epithelial cell function
Authors: Brown D.
Published: December 2017

The plasma membrane composition of virtually all eucaryotic cells is established, maintained, and modified by the process of membrane recycling. Specific plasma membrane components are inserted by exocytosis of transport vesicles, and are removed by endocytosis of segments of the membrane in which particular proteins are concentrated. In the kidney collecting duct, vasopressin induces the cycling of vesicles that are thought to carry water channels to and from the apical plasma membrane of principal cells, thus modulating the water permeability of this membrane. In the intercalated cells of the collecting duct, hydrogen ion secretion is controlled by the recycling of vesicles carrying proton pumps to and from the plasma membrane. In both cell types, "coated" carrier vesicles are involved, but whereas clathrin-coated vesicles participate in water channel recycling, the vesicles in intercalated cells are coated with the cytoplasmic domains of proton pumps. Following a brief outline of membrane recycling in general, this review summarizes previous data on membrane recycling in the collecting duct and related transporting epithelia and discusses some selected points relating to the role of membrane recycling and cell-specific function in the collecting duct.
Regulation of organic osmolyte concentrations in tubules from rat renal inner medulla
Authors: Wirthensohn G. , Lefrank S. , Schmolke M. , Guder W. G.
Published: December 2017

Glycerophosphorylcholine, inositol, and sorbitol were measured in rat kidney homogenates and tubules from inner medulla and papilla by enzymatic spectrophotometric techniques. Organic osmolytes exhibited their highest concentrations in the papillary tip. In contrast to glycerophosphorylcholine and sorbitol, inositol was of similar high concentrations in inner and outer medulla. Freshly prepared inner medullary tubules maintained tissue osmolyte concentrations under control, antidiuretic, and furosemide diuretic conditions. When tubules were incubated in vitro over 90 min, tubular organic osmolyte concentrations decreased as a function of extracellular NaCl, but not urea concentrations. Organic osmolyte disappearance from cells was quantitatively recovered from the medium. In contrast, medium lactate dehydrogenase activity did not rise in parallel and tubular ATP remained constant. Glucose up to a concentration of 200 mM increased tubule and medium sorbitol. The results obtained indicate that glycerophosphorylcholine, sorbitol, and inositol rapidly adapt their intracellular concentrations to extracellular NaCl osmolality by a change in tubular plasma membrane permeability. In addition sorbitol levels are regulated by the extracellular glucose concentration.
K activity of CCD principal cells from normal and DOCA-treated rabbits
Authors: Sansom S. C. , Agulian S. , Muto S. , Illig V. , Giebisch G.
Published: December 2017

We used liquid ion exchanger and conventional microelectrodes to evaluate the effects of mineralocorticoids on the intracellular K activity (aiK) and K transport properties of principal cells (PC) of isolated cortical collecting ducts (CCDs). Hoffman modulation optics and electrophysiological methods were used to identify PC. K activity was measured with two single-barreled electrodes. We found that aiK of PC from deoxycorticosterone acetate (DOCA)-treated rabbits (97.6 mM) was not different from controls (94.8 mM). The driving forces for K transport across the basolateral membrane favored cell to bath (reabsorption) in PCs from controls and bath to cell (secretion) in PCs from DOCA-treated rabbits. However, the driving force for K secretion across the apical membrane was not significantly different between the two groups. We used the intracellular aiKs and bath ion substitutions (gluconate for Cl and K for Na) to evaluate the effects of DOCA on the ion-selective properties of the basolateral membrane of PC. DOCA increased PK/PCl from 0.33 to 0.89. Our conclusion was as follows: in PC of control rabbits K is above electrochemical equilibrium across the basolateral membrane. However, the basolateral K conductance is probably too small for significant K recycling. In PC of DOCA-treated rabbits the aiK is below electrochemical equilibrium across the basolateral membrane and the K conductance is increased. These effects enhance K secretion across this border while maintaining cell K constant.
Low-conductance K channels in apical membrane of rat cortical collecting tubule
Authors: Frindt G. , Palmer L. G.
Published: December 2017

Low-conductance, K-selective channels were identified in the apical membrane of the rat cortical collecting tubule (CCT) by use of the patch-clamp technique. Isolated, split tubules were bathed in K gluconate medium to depolarize the cell while keeping the intracellular K concentration high. With the patch-clamp pipette containing predominantly either Na+ or Li+ but no K, outward currents were observed through channels that had a single-channel conductance (g) of 9 pS and a probability of being open (Po) of greater than 0.9, independent of the voltage (+/- 40 mV) applied to the pipette (Vp). Similarly, only outward currents were observed when the patch was excised into high-K solution, implying a high selectivity of the channel for K+. When 1 mM BaCl2 was added to the pipette, Po decreased to 0.36 at Vp = 0; however, g was not changed but the channels flickered rapidly between open and blocked states; Po decreased as Vp was made positive, and increased as Vp was made negative. With the pipette filled with KCl + 1 mM Ba, the channels conducted K+ in both directions. The inward currents (at positive Vp were larger than the outward currents (at negative Vp) and g near Vp = 0 increased to 25 pS. When the pipette was filled with RbCl + 1 mM Ba the inward and outward currents were similar in magnitude, suggesting that the channels can conduct Rb, although not as well as K. With the tubules bathed in NaCl Ringer solution and the pipette containing KCl, inward currents were observed that could be attributed to the same pathway for K.(ABSTRACT TRUNCATED AT 250 WORDS)
Intrarenal vasoconstriction during hyperchloremia: role of thromboxane
Authors: Bullivant E. M. , Wilcox C. S. , Welch W. J.
Published: December 2017

The role of thromboxane (Tx) in chloride-induced renal vasoconstriction was studied in Munich-Wistar rats. Hyperchloremia (induced by changing an intra-aortic, super-renal infusion of 1.2 M Na acetate to 1.2 M NaCl) reduced the glomerular filtration rate (GFR) by 31 +/- 3% (P less than 0.001; n = 27), and the clearance of p-aminohippurate (CPAH) by 36 +/- 4% (P less than 0.01). The Tx synthetase antagonists (25 mg/kg) UK-38,485 or OKY-046 prevented these changes. Pretreatment with indomethacin (5 mg/kg) also prevented Cl-induced changes in GFR and CPAH and blunted (P less than 0.05) the Cl-induced increase in renal vascular resistance (RVR, vehicle +55 +/- 11%, n = 8, indomethacin +27 +/- 7%, n = 6). Hyperchloremia reduced the hydraulic pressures (mmHg) in the outer cortical efferent arteriolar star vessels (PEA, 23.9 +/- 1.6 vs. 17.9 +/- 0.9; P less than 0.01) and proximal tubules (PT, 21.1 +/- 1.5 vs. 15.8 +/- 1.4; P less than 0.01) but not in the glomerular capillaries (PGC, 47.0 +/- 2.5 vs. 49.5 +/- 2.2; NS). Therefore the hydraulic pressure drop across the glomerular capillaries (PGC - PT) increased (24.9 +/- 2.8 vs. 34.6 +/- 2.9; P less than 0.02). UK-38,485 prevented significant Cl-induced changes in these pressures. The calculated resistances of the afferent and efferent arterioles both increased during hyperchloremia (+56 +/- 19%; P less than 0.05 and +195 +/- 66%; P less than 0.01, respectively) but were blunted after UK-38,485 (+23 +/- 8 and +21 +/- 10%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Differential permeabilities of rat renal brush-border and basolateral membrane vesicles
Authors: Lipkowitz M. S. , Abramson R. G.
Published: December 2017

Potassium chloride permeability and relative ionic conductances of rat renal cortical brush-border (BBMV) and basolateral (BLMV) membrane vesicles were examined using the fluorescent probe 3,3'-dipropylthiadicarbocyanine iodide [diS-C3-(5)]. Vesicles were simultaneously isolated and separated by free-flow electrophoresis. These studies demonstrated that neither BBMV nor BLMV equilibrated in 100 mM KCl despite prolonged incubation. In both, an inwardly directed KCl gradient was sustained for 3 h. The low intravesicular KCl concentration of BLMV was confirmed utilizing the response of electrogenic Na+-dependent [3H]glutamine transport to variations in the membrane potential. Chloride conductance was significantly less than potassium conductance in BBMV and BLMV. Consequently, an inside-positive potential was maintained across both membranes. BLMV were significantly more fluid, less permeable, had a lower relative chloride conductance, and maintained a greater inside-positive potential than BBMV. The KCl permeabilities of BBMV and BLMV were inversely related to endogenous membrane copper content and were significantly reduced by exogenous copper. Permeability did not correlate with membrane magnesium content, nor was it affected by exogenous magnesium. These studies suggest that endogenous copper as well as intracellular factors may regulate the permeabilities of the brush-border and basolateral membranes of proximal tubule cells in vivo.
Mechanism of the antiproteinuric effect of indomethacin in nephrotic humans
Authors: Golbetz H. , Black V. , Shemesh O. , Myers B. D.
Published: December 2017

To elucidate the mechanisms by which indomethacin lowers proteinuria, we studied 20 patients with the nephrotic syndrome. We performed differential macromolecule clearances before and after 3 days of therapy (150 mg/24 h). The fractional clearances of albumin and immunoglobulin G (IgG) decreased by 42 +/- 7 and 44 +/- 10%, respectively (P less than 0.05). Separation of IgG into fractions by preparative electrofocusing in eight selected individuals revealed a proportionate reduction of fractional clearances among anionic (pI = 5.0), neutral (pI = 7.5), and cationic species (pI = 8.5) of IgG. Indomethacin elevated the fractional clearance of uncharged dextrans of radius 28-44 A, while depressing those of dextrans of radius 50-60 A. A heteroporous model that depicts the major portion of the glomerular capillary wall as an isoporous membrane (pore radius = 56 A) and the minor portion as a nondiscriminatory shunt, revealed the former to be unchanged and the latter to be less prominent following indomethacin. A lower fraction of total filtrate volume permeating the shunt, together with a concomitant lowering of overall glomerular filtration rate by 24%, reduced the absolute rate of flux of macromolecule-rich fluid through the shunt pathway from 0.40 to 0.25 ml.min-1.73(-2) (P less than 0.01). We conclude that indomethacin lowered the filtered protein load by restoring barrier size-selectivity while reducing the rate of glomerular ultrafiltration.
Response to atrial natriuretic peptide in dogs with hypovolemic acute pancreatitis
Authors: Levy M. , Cernacek P.
Published: December 2017

The ability of atrial natriuretic peptide (ANP) to preserve renal function in dogs with hypovolemic acute renal insufficiency was tested in anesthetized dogs 4 h after the induction of acute pancreatitis. Plasma volume had decreased by 21.5% and glomerular filtration rate (GFR) by 43.2%. Blood pressure had declined by 30 mmHg. ANP was given intravenously at 50 and 150 ng.kg-1.min-1. With the lower dose, blood pressure (BP), GFR, and clearance of p-aminohippuric acid (CPAH) did not change but urine flow (V) and sodium excretion (UNaV) increased. With the higher dose, BP declined by 25 mmHg, GFR declined, but V and UNaV still increased. When plasma volume was maintained with 4% colloid during the progression of pancreatitis and ANP 50 ng.kg-1.min-1 given, BP declined, GFR did not change, and there was a magnified increment in V and UNaV. The administration of glucagon (5 micrograms/min iv) to dogs with hypovolemic pancreatitis caused BP to decline by 17 mmHg. Despite a major increment in GFR, fractional excretion of sodium increased only slightly, compared with that obtained with ANP. We conclude that glucagon preserves GFR more effectively than ANP in hypovolemia, but ANP is more effective in protecting urinary water and sodium excretion.
Na+-K+-ATPase activities in renal tubule segments of rat inner medulla
Authors: Terada Y. , Knepper M. A.
Published: December 2017

Recent studies have revealed that both the thin segment of the long loop of Henle and the inner medullary collecting duct (IMCD) are morphologically and functionally nonuniform along their lengths. In the present study, we have carried out measurements of Na+-K+-ATPase activity in thin limb and IMCD segments microdissected from different positions along the axis of the rat inner medulla. Among collecting duct segments, in control rats, Na+-K+-ATPase activity was highest in the initial quarter of the IMCD. The Na+-K+-ATPase activity was lower and relatively uniform along the remaining three quarters of the IMCD. Na+-K+-ATPase activities in cortical and outer medullary collecting duct segments were similar to previously reported values. The Na+-K+-ATPase activity in the initial quarter of the IMCD was increased following in vivo deoxycorticosterone administration (by 140%) and following dietary NaCl restriction (by 100%). These procedures increased Na+-K+-ATPase activity by smaller degrees or not at all in the remaining three-quarters of the IMCD. Thin descending limbs and thin ascending limbs from all regions of the inner medulla had low but readily measurable values. Based on these results, we conclude that all inner medullary renal tubule segments have measurable Na+-K+-ATPase activities that could potentially drive solute active transport.
Impaired preservation of GFR during hypotension in preexistent renal hypoperfusion
Authors: Yoshioka T. , Yared A. , Kon V. , Ichikawa I.
Published: December 2017

Autoregulation of renal blood flow and filtration rate was studied using micropuncture technique in Munich-Wistar rats with acute water deprivation (AWD) or congestive heart failure (CHF). In the first set of experiments, reduction of renal perfusion pressure to approximately to 70% of its initial value resulted in uncoupling of glomerular plasma flow rate and single-nephron glomerular filtration rate (GFR) (i.e., disproportionally profound fall in the latter) in AWD and CHF rats, whereas both indices changed little in normal control (NC) rats. The profound decrease in single-nephron GFR in AWD and CHF rats was primarily due to a reduction in glomerular capillary pressure (change from base-line value was -29 +/- 2% in AWD, -27 +/- 1% in CHF, and -8 +/- 2% in NC). This profound fall in glomerular capillary pressure in AWD and CHF rats was associated with a reduction in efferent arteriolar resistance, which contrastingly increased in NC. To investigate the mechanism underlying this unique efferent arteriolar responsiveness in AWD and CHF, the response of renal arterioles to exogenous angiotensin II was examined in separate groups of AWD, CHF, and NC. There was a markedly attenuated efferent arteriolar vasoconstrictive response in AWD and CHF (the change of efferent arteriolar resistance in both groups was some 5% of that in NC). Thus impairment in the ability to preserve GFR in these two conditions is attributed, at least in part, to altered efferent arteriolar response in the face of reduced renal perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Na-HCO3 cotransport and Na-H antiporter in chronic respiratory acidosis and alkalosis
Authors: Ruiz O. S. , Arruda J. A. , Talor Z.
Published: December 2017

Renal acidification in renal proximal tubule is thought to be mediated by luminal Na-H antiporter and the HCO3- generated by this antiporter is removed from the cell by a basolateral Na-HCO3 cotransporter. To study the effect of respiratory acid-base disorders on these transport systems, we have measured the Na-HCO3 cotransport in basolateral membranes and Na-H antiporter in luminal membranes in control rabbits, rabbits exposed to 10% CO2 (chronic hypercapnia), and rabbits exposed to 10% O2-90% N2 (chronic hypocapnia). The Vmax of HCO3(-)-dependent 22Na uptake was significantly higher in chronic hypercapnia than controls (2.54 +/- 0.03 vs. 1.18 +/- 0.21 nmol.mg protein-1.3 s-1, P less than 0.001). Likewise, the Vmax of the Na-H antiporter was also increased compared with controls (924.9 +/- 42.1 vs. 549.1 +/- 62.8 fluorescence units (FU).300 micrograms protein-1.min-1). In chronic hypocapnia, the Vmax of Na-HCO3 cotransport was lower than controls (0.72 +/- 0.11 vs. 1.18 +/- 0.21 nmol.mg protein-1.3 s-1, P less than 0.05). There was no difference, however, in the Vmax of the Na-H antiporter between hypocapnia and control (524.2 +/- 24.3 vs. 549.1 +/- 62.8, FU.300 micrograms protein-1.min-1). The Vmaxs of the Na-HCO3 cotransport and of the Na-H antiporter in hypocapnic, control, and hypercapnic rabbits were linearly related (r = 0.81), suggesting a simultaneous adaptation of the two systems in respiratory acid-base disorders.(ABSTRACT TRUNCATED AT 250 WORDS)
Facilitation by serum albumin of renal tubular secretion of organic anions
Authors: Besseghir K. , Mosig D. , Roch-Ramel F.
Published: December 2017

The role of albumin in tubular secretion of the organic anions p-aminohippurate (PAH, 21% albumin-bound at 1 microM) and methotrexate (MTX, 55% bound at 1 microM), and of the organic cation N1-methylnicotinamide (NMN, not bound), was investigated in isolated rabbit S2 proximal tubules. PAH or MTX secretory rates were low in the absence of colloids or in the presence of 1 g/dl dextran 40, and were reversibly two- to sevenfold stimulated by either 1 g/dl bovine (BSA, either regular, defatted, and/or dialyzed) or rabbit serum albumin, or by dialyzed native rabbit plasma. NMN secretion was not stimulated by either dextran or albumin. Luminal BSA had no effect, but stimulation of PAH secretion was observed when albumin was present in both lumen and bath. This secretion was BSA concentration-dependent up to a 1 g/dl BSA. Saturation experiments suggested that 1 g/dl BSA may increase PAH apparent affinity for secretion, with no change in its maximum velocity. Albumin appears therefore to facilitate organic anion proximal secretion by an effect unrelated to oncotic pressure or to the extent of organic anion binding.
Multiple transport systems for organic cations in renal brush-border membrane vesicles
Authors: Miyamoto Y. , Tiruppathi C. , Ganapathy V. , Leibach F. H.
Published: December 2017

The characteristics of guanidine uptake in brush-border membrane vesicles isolated from rabbit renal cortex were investigated. Guanidine uptake was markedly stimulated by an outwardly directed H+ gradient, resulting in a transient uphill transport. This stimulation was not due to an inside-negative, H+-diffusion potential because an ionophore-induced H+-diffusion potential and a K+-diffusion potential (both inside-negative) failed to enhance guanidine uptake. The H+ gradient itself appeared to be the driving force for the uptake. These data suggest that guanidine-H+ antiport (or guanidine-OH- symport) is the mechanism of guanidine uptake in these membrane vesicles. Guanidine uptake was only minimally inhibited by organic cations such as tetraethylammonium, N1-methylnicotinamide, and choline, but many other organic cations such as amiloride, clonidine, imipramine, and harmaline caused considerable inhibition. Uptake of radiolabeled guanidine was inhibited more effectively by guanidine than by tetraethylammonium, whereas uptake of radiolabeled tetraethylammonium was inhibited more effectively by tetraethylammonium than by guanidine. beta-Lactam antibiotics did not inhibit guanidine uptake but did inhibit tetraethylammonium uptake. Kinetic analysis showed that there were at least two kinetically distinct carrier systems for guanidine uptake, whereas tetraethylammonium uptake occurred via a single carrier system. These data provide evidence that renal brush-border membranes possess multiple carrier systems for organic cations.
Effect of epidermal growth factor on sodium transport in the cortical collecting tubule
Authors: Vehaskari V. M. , Hering-Smith K. S. , Moskowitz D. W. , Weiner I. D. , Hamm L. L.
Published: December 2017

Receptors for epidermal growth factor (EGF) have been demonstrated in the distal tubule. To determine whether there are acute functional correlates, we studied the effect of EGF on cortical collecting tubule (CCT) transepithelial voltage and transport of sodium and bicarbonate. Rabbit CCT were perfused in vitro and EGF was added to either the bathing medium or the luminal perfusate after base-line measurements of transport. Peritubular EGF in concentrations of 0.1 to 100 ng/ml (1.7 X 10(-11) to 1.7 X 10(-8) M) decreased sodium reabsorption, measured as 22Na absorption from the lumen, by 44-59%. There was a corresponding fall in the lumen-negative transepithelial voltage. Lower doses of EGF were without effect on transepithelial voltage or sodium transport. Pretreatment of the tubules with ouabain eliminated the effect of EGF on sodium transport. In contrast to peritubular EGF, luminal EGF (100 ng/ml) did not affect sodium transport. Peritubular EGF had no effect on either bicarbonate secretion or net bicarbonate transport in the CCT and no effect on net bicarbonate reabsorption in the medullary collecting tubule. Using the pH sensitive, fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, no change in principal cell intracellular pH was found after peritubular EGF. Two other growth factors, insulin and insulin-like growth factor I were without effect on sodium transport. We conclude that EGF inhibits active sodium absorption in CCT via receptors located at the basolateral membrane.
Bradykinin receptors localized by quantitative autoradiography in kidney, ureter, and bladder
Authors: Manning D. C. , Snyder S. H.
Published: December 2017

We have localized high affinity [3H]bradykinin receptor binding sites by in vitro autoradiography in kidney, ureter, and bladder of the guinea pig. The peptide pharmacology of the binding sites corresponds to that of high affinity physiological bradykinin receptors previously described (Manning, D. C., R. Vavrek, J. M. Stewart, and S. H. Snyder. J. Pharmacol. Exp. Ther. 237:504-512, 1986). In the kidney, receptors are concentrated in the medulla with negligible binding in the cortex. Medullary receptors are localized to the interstitium just beneath the basal membrane of collecting tubule cells and between tubules. In the ureter and bladder, receptors are confined to the lamina propria just beneath the epithelial layer. Localizations in the kidney may relate to the diuretic and natriuretic actions of bradykinin. Ureteral and bladder receptors may be associated with a role of bradykinin in pain and inflammation.
Primary sequence of Xenopus laevis Na+-K+-ATPase and its localization in A6 kidney cells
Authors: Verrey F. , Kairouz P. , Schaerer E. , Fuentes P. , Geering K. , Rossier B. C. , Kraehenbuhl J. P.
Published: December 2017

Polyclonal antibodies raised against the alpha- and beta-subunits of amphibian kidney Na+-K+-ATPase were used to screen an expression library from Xenopus laevis kidney epithelial cells (A6 cell line). cDNAs coding for each Na+-K+-ATPase subunit were identified and used to isolate near full-length cDNAs. The complete nucleotide sequence and the deduced amino acid sequence were determined. The alpha-subunit is an alpha (alpha I)-isoform. The alpha- and beta-subunits are more closely related to the mammalian and avian than the fish sequences. Antibodies raised against the fusion proteins produced by the two clones served to immunoprecipitate proteins from biosynthetically labeled or selectively surface-radioiodinated A6 cells grown on a porous substrate. The alpha- and the beta-subunits of Na+-K+-ATPase were found associated early in the course of biosynthesis and were restricted to the basolateral plasma membrane.
Brain ion and volume regulation during acute hypernatremia in Brattleboro rats
Authors: DePasquale M. , Patlak C. S. , Cserr H. F.
Published: December 2017

Regulation of brain ions and volume in response to 30 min of hypernatremia has been studied in two strains of anesthetized rats, the vasopressin-deficient Brattleboro and its vasopressin-competent parent strain, the Long-Evans. Plasma [Na] was increased by intraperitoneal injection of hyperosmolal NaCl. Brain volume was regulated during hypernatremia associated with tissue uptake of Na and Cl in both strains, but osmotically stimulated uptake of Na was 61% less in the Brattleboro. Blood-to-brain transfer constants for 22Na, measured as a function of plasma osmolality, were similar in the two strains. In contrast, bulk flow of cerebrospinal fluid (CSF) into brain, induced by osmotic dehydration of brain, was 55% less in the Brattleboro. CSF secretion in unstressed animals was also reduced, by 34%, in the Brattleboro compared with the Long-Evans. Reduced Na uptake by the brain of the Brattleboro rat during hypernatremia can be explained on the basis of a three-compartment model of brain volume regulation. Results support a function for vasopressin in brain ion homeostasis.
Galactose feeding causes glomerular hyperperfusion: prevention by aldose reductase inhibition
Authors: Bank N. , Coco M. , Aynedjian H. S.
Published: December 2017

Experimental dietary galactosemia is known to result in accumulation of the polyol, galactitol, via the aldose reductase metabolic pathway in a variety of tissues, including renal glomeruli. Because increased polyol accumulation also occurs in insulin-dependent diabetes mellitus (IDDM), in which marked renal glomerular hyperperfusion occurs, we have studied glomerular hemodynamics in rats with experimental galactosemia. Insulin deficiency and its accompanying metabolic disorders are not present in this experimental model. In additional groups of animals, aldose reductase inhibitors, either sorbinil or tolrestat, were added to the galactose diet. In all, five groups of rats were studied: regular diet, 50% galactose diet, regular diet plus sorbinil, 50% galactose diet plus sorbinil, and 50% galactose plus tolrestat. The diets were comparable in protein and salt, and the rats were pair fed. Micropuncture and whole kidney clearance measurements were carried out after 10-14 days on these diets. Compared with rats fed the regular diet, those fed with 50% galactose diet had significantly higher glomerular filtration rates, renal plasma flow, single-nephron glomerular filtration rates, and plasma flow (QA), whereas afferent vascular resistance (RA) was decreased. Addition of sorbinil or tolrestat to the high-galactose diet not only prevented renal hyperperfusion but RA and single-nephron filtration fraction (SNFF) were higher than in normal rats, and QA was lower. In addition, sorbinil administration to rats on the control diet caused significant decreases in single-nephron blood flow and the ultrafiltration coefficient and a rise in SNFF.(ABSTRACT TRUNCATED AT 250 WORDS)
Chloride and osmotic water permeabilities of isolated rabbit renal papillary surface epithelium
Authors: Packer R. K. , Sands J. M. , Knepper M. A.
Published: December 2017

The papillary surface epithelium (PSE) covers the mammalian renal papilla. It has been proposed that water or solute fluxes across the PSE might result in changes in urine or medullary interstitial fluid composition. To study osmotic water and chloride permeabilities, the PSE was dissected from underlying medullary tissue and mounted in a small Ussing chamber. Osmotic water permeability was low (14.2 +/- 3.0 microns/s) and was unaffected by 100 nM vasopressin added to the basolateral surface. In contrast, the PSE showed a substantial chloride permeability of 3.1 +/- 0.4 x 10(-5) cm/s that decreased reversibly to 2.2 +/- 0.3 x 10(-5) cm/s (P less than 0.01) with vasopressin. Vasopressin also reversibly increased the transepithelial resistance of the PSE from 87 +/- 9 to 106 +/- 13 omega.cm2 (P less than 0.02). Apical bumetanide (10(-6) M) had no significant effect on PSE chloride permeability. The apparent Na-Cl permeability ratio (0.75 +/- 0.01) calculated from dilution potential measurements was not affected significantly by vasopressin or apical bumetanide. We conclude that it is unlikely that physiologically significant osmotic water fluxes occur across the papillary surface epithelium. However, the NaCl permeability is sufficiently high that physiologically significant transepithelial NaCl fluxes could occur under conditions associated with reflux of urine backward from the papillary tip.
Dual regulation of insulin-like growth factor I expression during renal hypertrophy
Authors: Lajara R. , Rotwein P. , Bortz J. D. , Hansen V. A. , Sadow J. L. , Betts C. R. , Rogers S. A. , Hammerman M. R.
Published: December 2017

We examined the regulation of insulin-like growth factor I (IGF-I) in kidney during the renal hypertrophy produced by two different experimental models: growth hormone treatment of hypophysectomized rats and compensatory hypertrophy subsequent to unilateral nephrectomy. Immunostaining for IGF-I in collecting ducts was enhanced in kidneys from growth hormone-repleted hypophysectomized rats, and the levels of IGF-I mRNAs were increased. In compensatory hypertrophy, no enhancement of the intensity of immunostaining was observed in kidneys of nephrectomized rats until 5 days postnephrectomy, at which time immunostainable IGF-I was increased markedly in medullary collecting ducts of hypertrophied kidneys compared with kidneys from sham-operated animals. No difference in steady-state levels of any IGF-I mRNA species was detected in whole kidneys or in collecting ducts from nephrectomized or sham-operated rats at any time postnephrectomy. Our findings demonstrate an increase in both IGF-I mRNA and in immunostainable IGF-I in collecting duct in the setting of growth hormone-induced renal hypertrophy but suggest that other, possibly translational, mechanisms underlie the induction of IGF-I synthesis during compensatory hypertrophy.
Leukotriene D4 binding and signal transduction in rat glomerular mesangial cells
Authors: Badr K. F. , Mong S. , Hoover R. L. , Schwartzberg M. , Ebert J. , Jacobson H. R. , Harris R. C.
Published: December 2017

We examined the characteristics of [3H]leukotriene D4 (LTD4) binding to mesangial cells in culture. Binding is stereoselective, specific, saturable, and rapidly reversible. Two binding sites are recognized with dissociation constants and binding site densities at equilibrium of 2.2 and 16.8 nM and 1.1 x 10(4) and 3 x 10(4) binding sites per cell. LTD4, LTE4, (5R,6S)LTD4, LTB4, and the LTD4-receptor antagonist, SKF 104353, competitively inhibit radioligand binding in the following rank order of potency: LTD4 greater than LTE4 = SKF 104353 greater than (5R,6S)LTD4 greater than LTB4. LTD4 also induces time- and concentration-dependent phosphoinositide hydrolysis in mesangial cells. Formation of inositol 1,4,5-trisphosphate (IP3) is maximal at 5 s, followed by a time-dependent increase in inositol monophosphate generation, and inhibited by 100-fold excess concentration of SKF 104353. Addition of LTD4 to mesangial cells is associated with an increase in intracellular pH and dose-dependent stimulation of [3H]thymidine incorporation and mitogenesis. Thus rat mesangial cells possess specific binding sites for LTD4, the activation of which stimulates IP3 formation and induces cellular alkalinization and mitogenic responses. These studies provide insight into the cellular basis for LTD4-mesangial cell interactions, which are of potential pathophysiological relevance during acute glomerular inflammatory injury.
Autoradiographic localization of dopamine DA1 receptors in rat kidney with [3H]Sch 23390
Authors: Huo T. , Healy D. P.
Published: December 2017

Dopamine receptors in the rat kidney were characterized by homogenate binding and in vitro autoradiography using the dopamine 1 (DA1)-selective antagonist [3H]Sch 23390. [3H]Sch 23390 binding in cortical membrane preparations was saturable, stereoselective, and competed for by DA agonists and antagonists with a rank order of potency consistent with the labeling of the DA1 receptor. [3H]Sch 22390 binding was best fit to a two-site model: a high affinity-low density site (KD1 4.9 +/- 1.4 nM, Bmax 1 31.4 +/- 13.8 fmol/mg protein) and a low affinity-high density site (KD2 86.4 +/- 23.9 nM, Bmax 2 848.0 +/- 227.4 fmol/mg protein). In vitro autoradiography indicated that [3H]Sch 22390 binding sites were restricted to the cortex. High-resolution autoradiography further indicated that [3H]Sch 22390 binding sites were localized primarily on proximal tubules. Glomeruli and other vascular elements were devoid of [3H]Sch 23390 binding sites. These results suggest that DA and DA1 agonists may affect sodium excretion by a direct action on proximal tubule sodium reabsorption.
Effects of alpha-adrenergic agonists on intracellular and intramitochondrial pH in rat proximal nephrons
Authors: Gesek F. A. , Schoolwerth A. C.
Published: December 2017

Rat proximal tubular segments were used to examine alpha-adrenoceptor alterations in Na+-H+ exchange by monitoring intracellular pH (pHi) and mitochondrial matrix pH (pHm). To obtain pHi, tubules were incubated with the cell-permeant fluorescent probe, 2',7'-bis(2-carboxyethyl)-5(6) carboxyfluorescein acetoxymethyl ester in a HCO3--free Na+ buffer. The intracellular distribution of the weak acid [2-14C] 5,5-dimethyloxazolidine-2,4-dione was used to calculate pHm, using values of medium pH, pHi, cell volume, and matrix content. Several selective alpha 1- and alpha 2-adrenoceptor agonists and the endogenous mixed agonist, norepinephrine, all produced dose-related increases in pHi. With each of the agonists tested, a maximum increase in pHi was observed at 1 microM final concentrations, with peak effects occurring in less than 1 min. Pretreatment with ethylisopropyl amiloride (EIPA, 10 microM), a specific inhibitor of proximal Na+-H+ exchange, blocked receptor-stimulated increases in pHi, as well as stimulation of Na+-H+ exchange by phorbol ester (PMA, 0.1 microM). Similarly, selective alpha 1- (prazosin, 0.1 microM) and alpha 2-(idazoxan, 0.1 microM) adrenoceptor antagonists inhibited alterations in agonist-induced pHi changes, whereas PMA-stimulated increases in pHi remained unaffected. Neither alpha 1- nor alpha 2-adrenoceptor agonists produced differences in pHm. Adrenoceptor agonist-induced pHi changes were also assessed at various concentrations of external Na+ (0-135 mM). It was observed that 0 and 10 mM external Na+ concentrations significantly reduced alpha 1- and alpha 2-adrenoceptor-stimulated pHi changes; Km values for the alpha 1-agonist phenylephrine and the alpha 2-agonist B-HT 933 were 18.0 +/- 2.1 and 22.7 +/- 2.6, respectively. In summary, stimulation by alpha-adrenergic agonists may be blocked at the receptor level with specific alpha-antagonists or at the exchanger with EIPA. The increase in cellular pH induced by these agonists is sensitive to external Na+ and reflects alpha-adrenoceptor activation of the Na+-H+ exchanger.
Decrease in ureagenesis by partial hepatectomy does not influence acid-base balance
Authors: Almdal T. , Vilstrup H. , Bjerrum K. , Kristensen L. O.
Published: December 2017

It has been suggested that urea synthesis participates directly in body pH homeostasis by removal of bicarbonate. To elucidate this hypothesis sodium bicarbonate or sodium chloride was infused (11.5 mumol/min) for 90 min into control rats and into rats that had undergone an 85% hepatectomy immediately before starting the infusion. Urea synthesis rate was 2.6 +/- 0.3 mumol/min (mean +/- SE) in controls, and was significantly (P less than 0.01) reduced to 1.0 +/- 0.2 mumol/min in partially hepatectomized rats. At the start of bicarbonate infusion, pH was 7.38 and 7.34 in control and partially hepatectomized rats, respectively, and at the end of infusion, pH was 7.56 and 7.51. Standard bicarbonate at start of bicarbonate infusion was 21.9 and 21.3 mM in controls and partially hepatectomized, respectively, and it increased to 32.7 and 29.9 mM at end of infusion. In saline-infused rats a slight decrease of approximately 0.05 pH units was observed during the experiment, but again no difference emerged between control and partially hepatectomized rats. It is concluded that a major role of the liver in the regulation of acid-base balance is unlikely.
Essential fatty acid deficiency during acute puromycin nephrosis ameliorates late renal injury
Authors: Diamond J. R. , Pesek I. , Ruggieri S. , Karnovsky M. J.
Published: December 2017

Puromycin aminonucleoside (PA) nephrosis is associated with a significant increase in the glomerular macrophage number during peak proteinuria. The significance of this observation remains uncertain. An essential fatty acid-deficient (EFAD) diet depletes normal rat glomeruli of resident macrophages and alters glomerular eicosanoid metabolism. In this study, we found that an EFAD diet, administered only for the duration of the acute nephrotic phase, significantly ameliorated the recurrent albuminuria, renal dysfunction, and morphological injury characteristic of the late, recurrent phase of chronic aminonucleoside nephrosis. Glomerular macrophage number, isolated glomerular thromboxane B2 production, and circulating leukocyte and monocyte counts were significantly reduced in nephrotic rats on the EFAD diet 2 wk after PA injection, which temporally corresponds to peak albuminuria. The exact mechanism(s) by which the EFAD diet conferred protection in the late phase of chronic aminonucleoside nephrosis and lowered glomerular macrophage number during the acute nephrotic phase remain to be elucidated.
Transport-coupling hypothesis of tubuloglomerular feedback signal transmission
Authors: Rich A. , Moore L. C.
Published: December 2017

A mathematical model was used to explore the transport-coupling hypothesis of tubuloglomerular feedback (TGF) signal transmission from the macula densa (MD) to the extraglomerular mesangium (EGM) within the juxtaglomerular apparatus (JGA). The transport-coupling hypothesis supposes that changes in MD transport alter the ionic composition of the EGM interstitium, thereby stimulating the Goormaghtigh cells. This hypothesis is based on the avascularity of the EGM and the presence of a narrow cleft (JGA cleft) between the MD and Goormaghtigh cells. The model describes NaCl and water transport by MD cells and mass conservation in the JGA cleft. It calculates cleft water flow and NaCl concentration [( NaCl]). If the cleft is narrow, the model predicts that cleft [NaCl] will vary directly with luminal [NaCl] and net MD NaCl transport. With strong active NaCl transport, the MD cell plaque may act as an ionic amplifier, in that small changes in luminal [NaCl] might elicit much larger concentration changes within the cleft. Even without active NaCl transport, cleft [NaCl] could remain coupled to luminal [NaCl] if the MD cells passively secrete NaCl. With high hydraulic conductivity, cleft [NaCl] also varies with luminal osmolarity. With a wide cleft, a low diffusional resistance of the EGM interstitium, or swollen MD lateral intercellular spaces, the transport coupling between cleft and luminal [NaCl] is markedly attenuated. The predictions of our model of large changes in JGA interstitial composition agree well with published measurements made in Amphiuma. However, the low Na+-K+-ATPase content and high water permeability of mammalian MD suggest that the transport-coupling effects in mammals may be significantly less pronounced than in Amphiuma.
Characterization of the major brain osmolytes that accumulate in salt-loaded rats
Authors: Heilig C. W. , Stromski M. E. , Blumenfeld J. D. , Lee J. P. , Gullans S. R.
Published: December 2017

Previous studies demonstrated an accumulation of “idiogenic osmoles” in the brain with chronic salt loading. Amino acids are known to constitute a portion of these solutes, but the balance of the solutes has yet to be fully characterized. In the present study, 1H-nuclear magnetic resonance (NMR) spectroscopy and biochemical assays of rat brain were used to identify and quantify changes in organic solutes in two different animal models of hypernatremia: hypertonic salt loading and water deprivation. Five days of salt loading increased plasma sodium concentration (PNa) to 165 meq/l and 3 days of water deprivation increased PNa to 151 meq/l, compared with 141 meq/l in controls. Amino acids, methylamines, and polyols were all significantly higher in salt-loaded animals compared with controls. Specifically, higher contents of glutamine (+65%), glutamate (+27%), myo-inositol (+36%), phosphocreatine + creatine (PCr + Cr) (32%), glycerophosphorylcholine (GPC) (+75%), and choline (+114%) were observed. Sorbitol and betaine, osmolytes known to accumulate in the hypertonic inner medulla, were present in low amounts in the brain and were unchanged with salt loading. In contrast to the results with salt loading, no accumulation of brain organic solutes was detected after 3 days of water deprivation. Based on these findings, we propose that amino acids, methylamines, and polyols function as osmoregulatory solutes in the brains of salt-loaded rats in a manner similar to that observed in other biological systems, whereas 3 days of water deprivation is an insufficient stimulus for their accumulation.
Methylamine and polyol responses to salt loading in renal inner medulla
Authors: Heilig C. W. , Stromski M. E. , Gullans S. R.
Published: December 2017

Methylamines and polyhydric alcohols (polyols) are major organic osmolytes of the mammalian renal inner medulla and have generally been noted to change in parallel with urine osmolality. In the present study, responses of inner medullary methylamines and polyols to 5 days of salt loading were investigated. Salt loading increased plasma sodium concentration and induced a saline diuresis that resulted in a significantly lower urine osmolality (Uosmol) in salt-loaded rats (1,246 mosmol) compared with controls (2,147 mosmol). Analysis of inner medullary organic osmolytes using 1H-NMR spectroscopy and biochemical assays indicated no significant change in total methylamines, total polyols, or total osmolytes with salt loading. However, there were marked changes in individual organic osmolytes. Renal inner medullary glycerophosphorylcholine (GPC) was 41% lower in salt-loaded rats, and was the only organic osmolyte that changed in parallel with Uosmol, which was 42% lower in this group. In contrast, glycine betaine (betaine) and sorbitol contents were elevated by 286% and 33%, respectively, with salt loading, and myo-inositol (inositol) was unchanged. These findings indicate selective renal inner medullary osmolyte responses to salt loading with only GPC varying directly with changes in urine osmolality.