A calcium-dependent transient outward current in Xenopus laevis oocytes

Abstract

Membrane currents were investigated in Xenopus laevis oocytes under voltage clamp. Depolarizing pulses, given from a holding potential of about -- 100 mV, elicited a transient outward current when the membrane potential was made more positive than about -- 20 mV. As the potential was made increasingly positive the transient outward current first increased and then decreased. The amplitude of the transient current increased when the external Ca$^{2+}$ concentration was raised; and the current was abolished by Mn$^{2+}$. It appears that when the membrane is depolarized Ca$^{2+}$ ions enter the oocyte and trigger an outward current, possibly by opening Cl$^{-}$ channels.