CALCIUM CURRENTS RECORDED FROM A NEURONAL ALPHA(1C) L-TYPE CALCIUM-CHANNEL IN XENOPUS-OOCYTES

Xenopus oocytes expressing neuronal alpha(1C), alpha(2) and beta(1b) c alcium channel subunit cDNAs were used in this study. During two-elect ric voltage clamp recording the oocyte was injected with 10-20 nl of a 100 mM BAPTA solution. Under these conditions, the endogenous Ca-acti vated Cl current was completely suppressed resulting in an alpha(1C) B a current free from Cl current contamination. BAPTA injection also all owed alpha(1C) currents with different permeating ions, including Ca, to be examined. Compared to Ba and Sr, alpha(1C) whole cell Ca current s were smaller in magnitude and showed kinetic and voltage-dependent p roperties more similar to those for L-type Ca currents recorded in nat ive cells. That Ca-dependent inactivation occurs in BAPTA-buffered cel ls suggests that the Ca-binding site involved in this type of inactiva tion is very close to the pore of the channel.