PROPERTIES OF THE CA2-ACTIVATED CL- CURRENT OF XENOPUS OOCYTES()

The properties of the Ca2+-activated Cl- current of Xenopus oocytes ha ve been investigated by voltage-clamp and injections of D-3-deoxy-3-fl uoro-myo-inositol 1,4,5-trisphosphate (3-F-InsP(3)). Following 3-F-Ins P(3) injection, a transient phase of Ca2+-activated Cl- current occurr ed, caused by Ca2+ release from internal stores. subsequently, a secon dary, long-lasting, current was recorded, signaling Ca2+ influx from t he exterior (I-CRAC). Changes in external Cl- during the sustained pha se produced the expected shifts in reversal potential (E-rev), while t he conductance varied opposite to the predictions of simple electrodif fusional theory. Application of depolarizing pulses soon (10 s after 3 -F-InsP, injection elicited membrane currents exhibiting a single expo nential rise. During the sustained subsequent phase, the current elici ted by depolarizations showed an early pe:tk followed by a prominent d ecline. During the sustained phase, removal of calcium from the extern al solution, or its substitution with Ba2+. abolished voltage- and tim e-dependent components of the depolarization-induced current. Slope co nductance analysis of the inactivating records revealed, ill addition to the decline of the Ca2+-activated Cl- current, the presence of a se cond, inwardly directed current. This could be identified as a slowly inducible Na+ current already described in Xenopus oocytes.