AJP - Cell Physiology, Vol 254, Issue 6 C816-C821, Copyright © 1988 by American Physiological Society
Activation of K+ conductance in basolateral membrane of toad urinary bladder by oxytocin and cAMP
W. Van Driessche and D. Erlij
Laboratorium voor Fysiologie, Campus Gasthuisberg, Leuven, Belgium.
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.
