title: Drugs activating G proteins disturb cycling of ADH-dependent water channels in toad urinary bladder.
abstract: 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%. 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.
authors.affiliation: Laboratoire de Physiologie et de Physiopathologie, Université Libre de Bruxelles, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Boom
authors.forename: B
authors.initials: B
authors.lastname: Flamion
authors.forename: M
authors.initials: M
authors.lastname: Abramow
authors.forename: R
authors.initials: R
authors.lastname: Beauwens
mesh_terms: D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002024:Bufo marinus; D017097:Electric Impedance; D004705:Endocytosis; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D009995:Osmosis; D010455:Peptides; D001743:Urinary Bladder / Q000378:metabolism* / Q000502:physiology; D014667:Vasopressins / Q000502:physiology*; D014862:Wasp Venoms / Q000494:pharmacology; D014867:Water / Q000378:metabolism*; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology
chemical_list: D017607:Aluminum Compounds; D036341:Intercellular Signaling Peptides and Proteins; D007473:Ion Channels; D010455:Peptides; D014862:Wasp Venoms; D014867:Water; D014667:Vasopressins; D003189:p-Methoxy-N-methylphenethylamine; C037500:mastoparan; D019204:GTP-Binding Proteins; D005459:Fluorides; C032311:aluminum fluoride