Properties of the Ca(2+)-activated Cl- current of Xenopus oocytes

Abstract

The properties of the Ca(2+)-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-lnsP3). Following 3-F-InsP3 injection, a transient phase of Ca(2+)-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 (ICRAC). Changes in external Cl- during the sustained phase produced the expected shifts in reversal potential (Erev), 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 Ca(2+)-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.