Chloride current induced by injection of calcium into Xenopus oocytes.

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Abstract
Membrane currents of Xenopus oocytes were studied with the membrane under voltage clamp. Intracellular injection of the Ca-chelating agent, EGTA [ethyleneglycol-bis(.beta.-aminoethyl)-N,N''-tetraacetic acid], reduced, or abolished, the transient outward Cl current normally activated by membrane depolarization. Intracellular injection of Ca ions evoked largely membrane currents, which inverted direction close to the Cl equilibrium potential. Injections of Sr, or Ba, were less effective than Ca, while Mg was ineffective. Large Cl currents could be evoked by Ca injections in oocytes which showed only small or no transient outward currents. The current activated by Ca injection increased with increasing depolarization, up to high (+60 mV) positive potentials, even though the transient outward current was suppressed by strong depolarization. The transient outward current evidently depends upon entry of Ca through voltage-gated Ca ion channels. The oocyte membrane contains numerous Cl channels which are activated by intracellular Ca. Only a few of these Cl channels are activated by depolarization.