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) calcium channel subunit cDNAs were used in this study. During two-electric voltage clamp recording the oocyte was injected with 10-20 nl of a 100 mM BAPTA solution. Under these conditions, the endogenous Ca-activated Cl current was completely suppressed resulting in an alpha(1C) Ba current free from Cl current contamination. BAPTA injection also allowed alpha(1C) currents with different permeating ions, including Ca, to be examined. Compared to Ba and Sr, alpha(1C) whole cell Ca currents were smaller in magnitude and showed kinetic and voltage-dependent properties more similar to those for L-type Ca currents recorded in native cells. That Ca-dependent inactivation occurs in BAPTA-buffered cells suggests that the Ca-binding site involved in this type of inactivation is very close to the pore of the channel.