Oxytocin stimulates the apical K+ conductance in frog skin

We measured the effects of oxytocin (0.1 U/ml) on the current (Isc) recorded through skins of Rana temporaria incubated with an isotonic K+ solution on the apical side while the transepithelial potential was clamped to zero. Under these conditions, Isc is carried by inward K+ movements. Oxytocin markedly stimulated this inward K+ current. When the spontaneous fluctuations were analyzed we found that oxytocin increased the plateau (S(1)o) of the spontaneous Lorentzian component without modifying the corner frequency (f(1)c). Addition of Ba2+ to the mucosal solution blocked Isc both in the presence and absence of oxytocin. Moreover, with mucosal Ba2+ a characteristic blocker-induced Lorentzian component appeared in the power spectrum. Analysis of this blocker-induced noise showed that oxytocin increased the number of active K+ channels in the apical membrane, while the changes in single channel current were in agreement with the expected alterations of the electrochemical driving force.