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

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-InsP(3)). Following 3-F-InsP(3) 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-InsP, injection elicited membrane currents exhibiting a single exponential rise. During the sustained subsequent phase, the current elicited by depolarizations showed an early pe:tk 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, ill 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.