Properties of the Ca2+-activated Cl− current of Xenopus oocytes

Abstract.

The properties of the Ca²⁺-activated Cl⁻ current of Xenopus oocytes have been investigated by voltage-clamp and injections of D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-InsP₃). Following 3-F-InsP₃ injection, a transient phase of Ca²⁺-activated Cl⁻ current occurred, caused by Ca²⁺ release from internal stores; subsequently, a secondary, long-lasting, current was recorded, signaling Ca²⁺ influx from the exterior (I_CRAC). Changes in external Cl⁻ during the sustained phase produced the expected shifts in reversal potential (E_rev), while the conductance varied opposite to the predictions of simple electrodiffusional theory. Application of depolarizing pulses soon (10 s) after 3-F-InsP₃ injection elicited membrane currents exhibiting a single exponential rise. During the sustained subsequent phase, the current elicited by depolarizations showed an early peak followed by a prominent decline. During the sustained phase, removal of calcium from the external solution, or its substitution with Ba²⁺, abolished voltage- and time-dependent components of the depolarization-induced current. Slope conductance analysis of the inactivating records revealed, in addition to the decline of the Ca²⁺-activated Cl⁻ current, the presence of a second, inwardly directed current. This could be identified as a slowly inducible Na⁺ current already described in Xenopus oocytes.