A Calcium-Dependent Transient Outward Current in Xenopus laevis Oocytes

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 Ca2+ concentration was raised; and the current was abolished by Mn2+. It appears that when the membrane is depolarized Ca2+ ions enter the oocyte and trigger an outward current, possibly by opening Cl– channels.