Exocytotic events unrelated to regulation of water permeability in amphibian tight epithelia: effects of oxytocin, PMA and insulin on membrane capacitance, water and Na+ transport.
We measured the effects of oxytocin on capacitance and hydroosmotic water flow in the urinary bladder of the toad Bufo marinus and the skins of Rana pipiens and Rana temporaria. Oxytocin increased capacitance in all these tissues but stimulated hydroosmotic water flow only in the urinary bladder. We also measured the effects of oxytocin and PMA on the capacitance and hydroosmotic water flow of the toad urinary bladder. Both agents produced increases in membrane capacitance that were additive, however, PMA produced a stimulation of water flow that was only a fraction of that caused by oxytocin. Comparison of the effects of PMA and insulin in toad urinary bladder showed that in contrast with PMA, insulin did not increase membrane capacitance in this tissue. Moreover, insulin stimulated Isc in the urinary bladder while PMA produced an inhibition of variable magnitude. These results suggest that: (1) oxytocin can promote the fusion with the apical membrane of cytoplasmic membranes with or without water channels; (2) oxytocin and PMA stimulate the fusion with the apical membrane of cytoplasmic membranes originating in different pools; membranes in each pool have different water permeabilities and their insertion is controlled by different signals; (3) PMA and insulin act through different mechanisms in the toad urinary bladder.
Erlij
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Department of Physiology, SUNY, Downstate Medical Center, Brooklyn 11203.
Aelvoet
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Van Driessche
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D000818:Animals; D001834:Body Water / Q000502:physiology; D002024:Bufo marinus; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D010121:Oxytocin / Q000494:pharmacology*; D010539:Permeability; D011894:Rana pipiens; D011896:Rana temporaria; D012867:Skin / Q000187:drug effects; D012879:Skin Physiological Phenomena; D012964:Sodium / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D007328:Insulin; D010121:Oxytocin; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate