ANION-INDUCED DYNAMIC BEHAVIOR OF APICAL WATER CHANNELS IN VASOPRESSIN-SENSITIVE EPITHELIA EXPOSED TO MERCURY

We showed recently that, in toad skins preexposed to Hg, water permeab ility is high in SO4-Ringer and low in Cl-Ringer. This anion effect wa s further investigated in Hg-treated skins and bladders of toads (Bufo marinus) in a variety of experimental conditions, including glutarald ehyde fixation and stimulation by vasopressin (VP) or isoproterenol (I P). In fixed bladders either unstimulated or stimulated with VP, net w ater flow (J(w)) in SO4-Ringer [J(w) (SO4)] was always significantly h igher than J(w) in Cl [J(w) (Cl)]; the same applies to fixed toad skin s, either unstimulated or stimulated with IP. In unfixed isolated toad epidermis challenged with IP before Hg exposure, J(w)(SO4)/J(w)(Cl) > > 1 approaching the ratio J(w) (maximally stimulated)/J(w) (basal). Th erefore, anion-induced J(w) changes were present whether Hg acted on e pithelial water channels exocytosed by Hg itself or by hydrosmotic age nts and suggest a switching between open and closed configurations of the channel protein. This anion effect was not abolished by glutaralde hyde and might be correlated with changes in intracellular chloride.