Drugs activating G proteins disturb cycling of ADH-dependent water channels in toad urinary bladder.

In the toad urinary bladder, antidiuretic hormone (ADH)-mediated changes in water permeability depend on exocytic insertion and endocytic retrieval of water channels into and from the apical membrane, respectively. Because GTP-binding proteins (G proteins) are well-recognized regulators of vesicular trafficking throughout the cell, we tested the hypothesis that drugs interfering with G protein would modify the hydrosmotic response to ADH and the ADH-regulated formation of endosomes, as assessed by luminal incorporation of a fluid-phase marker [fluorescein isothiocyanate (FITC)-dextran, 70 kDa]. Mastoparan (4 microM) and compound 48/80 (poly-p-methoxyphenylethylmethylamine; 50 micrograms/ml), added to the luminal side of the toad urinary bladder, as well as AlF3 added to the serosal side (400 microM), inhibited ADH- and 8-bromoadenosine 3',5'-cyclic monophosphate-induced transepithelial water flow by > 50% and simultaneously enhanced cellular incorporation of FITC-dextran by > 200%.

Aldosterone stimulation of GTP hydrolysis in membranes from renal epithelia.

Specific hydrolysis of GTP catalyzed by membranes prepared from A6 epithelial cells grown on porous supports was measured. Aldosterone treatment of the cells for 4 h increased Na+ transport and stimulated GTP hydrolysis by apical membranes in vitro more than twofold over basal levels. This stimulation was attributed to an increase in maximum velocity with little change in Michaelis-Menten constant values.

Adaptation of inner medullary collecting duct to dehydration involves a paracellular pathway.

Prolonged fluid restriction in rats is accompanied by functional modifications of the terminal part of the inner medullary collecting duct (IMCD) revealed by a sustained increase in arginine vasopressin (AVP)-independent transepithelial osmotic water permeability (PTE) in vitro. The cellular basis of this adaptation was explored in isolated and perfused terminal IMCDs of Sprague-Dawley rats using video and fluorescence microscopy. Basolateral membrane osmotic water permeability (Posm), transcellular Posm, and PTE were measured in quick sequence in every tubule.

Subtypes of Madin-Darby canine kidney (MDCK) cells defined by immunocytochemistry: further evidence for properties of renal collecting duct cells.

The Madin-Darby canine kidney (MDCK) cell line has been proposed as a model for studying intercalated (IC) cells of the renal cortical collecting duct. The IC cells are characterized by peanut lectin (PNA) binding capacity, carbonic anhydrase (CA) activity and Cl(-)-HCO3- exchange mediated by a band 3-related protein. It has been suggested that these properties are also expressed in MDCK cells.

Aldosterone-induced and GTP-stimulated methylation of a 90-kDa polypeptide in the apical membrane of A6 epithelia.

Aldosterone treatment of A6 cultured renal epithelial cells methylates the apical membrane, and we examined the aldosterone-induced carboxymethylation of the apical membrane of these cells to determine the targeted polypeptides. Methionine-deprived A6 cells were incubated with aldosterone and [3H]methionine. Homogenates and apical membranes were solubilized and analyzed by SDS-polyacrylamide gel electrophoresis.

Single-channel behavior of a purified epithelial Na+ channel subunit that binds amiloride.

The apical membrane of high electrical resistance epithelia, which is selectively permeable to Na+, plays an essential role in the maintenance of salt balance. Na+ entry from the apical fluid into the cells is mediated by amiloride-blockable Na(+)-specific channels. The channel protein, purified from both amphibian and mammalian sources, is composed of several subunits, only one of which the 150-kDa polypeptide, specifically binds the Na+ transport inhibitor amiloride.

The iodide channel of the thyroid: a plasma membrane vesicle study.

The uptake of radioactive iodide or chloride by plasma membrane vesicles of bovine thyroid was studied by a rapid filtration technique. A Na(+)-I- cotransport was demonstrated. When this Na(+)-I- cotransport is inactive (i.

Impaired hydroosmotic response to vasopressin of cortical collecting tubules from lithium-treated rabbits.

The hydroosmotic action of [arginine]vasopressin (vasopressin, 25 microU/ml) and of 8-Br-cAMP (10(-4)M) was studied in vitro in perfused cortical collecting tubules (CCT) isolated from rabbits fed with lithium chloride for 3 weeks. Vasopressin-dependent water reabsorption was significantly inhibited by 65% although no lithium was used in the in vitro experiments. The hydroosmotic action of 8-Br-cAMP was also inhibited by previous Li treatment, but the effect was smaller in magnitude.

Atrial natriuretic peptides in canine hypoxic pulmonary vasoconstriction.

Study Objective: The aim of the study was to investigate whether atrial natriuretic peptides have a physiological role in regulation of the pulmonary circulation.

Design: Plasma concentrations of immunoreactive atrial natriuretic peptide and guanosine-3',5'-cyclic monophosphate (cGMP) were measured during evaluation of pulmonary vascular tone by multipoint pulmonary arterial pressure-cardiac index (Ppa/Q) relationships.

Subjects: Experimental animals were 17 mongrel dogs of either sex, 21-35 kg weight, anaesthetised with pentobarbitone.

Pharmacological doses of atrial natriuretic factor do not inhibit canine hypoxic pulmonary vasoconstriction.

It has been recently suggested that atrial natriuretic factor (ANF) might be involved in the physiological regulation of pulmonary circulation. Therefore, we investigated the pulmonary hemodynamic response to 20-min infusions of 0.05, 0.

Natriuresis and atrial natriuretic factor secretion during inappropriate antidiuresis.

The mechanisms responsible for the natriuresis encountered in the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are not fully understood. The present study explores the role of atrial natriuretic factor (ANF). Eight subjects unable to excrete ingested free water normally (three patients with SIADH and five healthy humans after intranasal administration of desmopressin) underwent a standard oral water loading test.

Mechanisms of lithium-vasopressin interaction in rabbit cortical collecting tubule.

In single cortical collecting tubules (CCT) of the rabbit, guanosine 5'-triphosphate (GTP) increased the arginine vasopressin (AVP)-stimulated adenylate cyclase (AC) by 60% (P less than 0.05). In contrast, guanosine 5' O-(2-thio)-diphosphate (GDP-beta S), a competitive inhibitor of GTP action on the stimulatory guanine regulatory protein (Ns), reduced the AVP-stimulated AC activity by 72% (P less than 0.

Inhibition by lithium of the hydroosmotic action of vasopressin in the isolated perfused cortical collecting tubule of the rabbit.

Because treatment with lithium salts may impair renal concentrating ability, we investigated the possibility of a direct effect of lithium ions on the permeability to water of the collecting duct epithelium. The coefficient of hydraulic conductivity (Lp) of isolated perfused rabbit cortical collecting tubules (CCT) was measured in the presence and absence of arginine-8-vasopressin (AVP), or 8-bromo (Br) cyclic AMP (cAMP) and/or lithium chloride (Li 10 mM). In the absence of AVP, Li in the lumen for 30 min failed to affect basal water permeability; however, in tubules preincubated with Li in the lumen for 80 min, basal water permeability was reduced to 30% of the value found in control tubules (P less than 0.

Transient hyperthyroxinemia in symptomatic hyponatremic patients.

Twenty-two patients with severe hyponatremia were divided into 12 patients with and ten without associated neurologic manifestations (groups 1 and 2, respectively). Marked hyperthyroxinemia was demonstrated in seven patients in group 1 but in none in group 2. The triiodothyronine concentration was also higher than normal in two patients in group 1.