Activation of K+ conductance in basolateral membrane of toad urinary bladder by oxytocin and cAMP.
We incubated toad urinary bladders with Na+-free, isotonic K+ solutions on the apical side and increased the cationic conductance of the apical membrane with nystatin (150 U/ml). Under these conditions, the short-circuit current is mostly carried by K+ flowing from mucosa to serosa. Impedance measurements showed that in nystatin-treated preparations, the electrical behavior of the tissue is dominated by the basolateral membrane properties. Oxytocin (0.1 U/ml) produced an increase of the current and the conductance of the basolateral membrane. Both the resting and the oxytocin-stimulated current were rapidly and reversibly blocked by serosal Ba2+. Addition of the adenosine 3',5'-cyclic monophosphate (cAMP) analogue [8-(4-chloropheylthio)-cAMP] to the basolateral solution mimicked the effects of oxytocin. These results show that oxytocin and cAMP stimulate a potassium conductance in the basolateral membrane and that the stimulation is not related to an increase in sodium entry through the apical membrane. Addition of ouabain (10(-3) M) to the serosal solution did not modify the stimulation by oxytocin, indicating that the activated pathway is not linked to the rate of turnover of the Na+ pump.
Van Driessche
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Laboratorium voor Fysiologie, Campus Gasthuisberg, Leuven, Belgium.
Erlij
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D
D000818:Animals; D002024:Bufo marinus; D000242:Cyclic AMP / Q000494:pharmacology*; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D009761:Nystatin / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects* / Q000378:metabolism
D009761:Nystatin; D010121:Oxytocin; D000242:Cyclic AMP; D011188:Potassium