Drugs activating g-proteins disturb cycling of adh-dependent water channels in the toad urinary bladder. Boom, Alain, Bruno Flamion, Maurice Abramow, and Renaud Beauwens. Laboratoire de Physiologie et de Physiopathologie, Campus Erasme, Universit[acute]e Libre de Bruxelles, 1070 Brussels, Belgium.
APStracts 2:0096C, 1995.
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. Since 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 hydroosmotic response to ADH and the ADH-regulated formation of endosomes as assessed by lumenal incorporation of a fluid phase marker (FITC-dextran 70kD). Mastoparan (4[mu]M) and compound 48/80 (50[mu]g/ml), added to the lumenal side of the toad urinary bladder, as well as aluminium fluoride (AlF3) added to the serosal side (400[mu]M), inhibited ADH- and 8-br-cAMP-induced transepithelial water flow by more than 50% and simultaneously enhanced cellular incorporation of FITC-dextran by more than 200%. The pattern of FITC -dextran uptake observed using fluorescence microscopy both in scraped cells and in the intact bladder was granular, suggesting fluid phase endocytosis. Mastoparan and AlF3, which are both probes of G -proteins, increased FITC-dextran uptake only in the presence of ADH and a transepithelial osmotic gradient, i.e., under conditions where water channel-carrying endosomes presumably cycle. Therefore, we suggest that the ADH-dependent cycling of water channels could be controlled by one or more G-proteins associated with the apical membrane and/or the water channel-carrying vesicles. 

Received 6 June 1994; accepted in final form 26 January 1995.
APS Manuscript Number C309-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.