POTENTIATION BY THE BETA-SUBUNIT OF THE RATIO OF THE IONIC CURRENT TOTHE CHARGE MOVEMENT IN THE CARDIAC CALCIUM-CHANNEL

The voltage-activated rabbit cardiac calcium channel alpha1 subunit wa s expressed in Xenopus oocytes. The charge movement of its voltage sen sor was measured and related to the opening of the ion-conducting pore . The half-activation potential for charge movement was 35 millivolts more negative than that for pore opening. Coexpression of the cardiac calcium channel beta subunit reduced this difference without affecting charge movement. Thus, intramolecular coupling between the voltage se nsor and the channel pore opening can be facilitated by a regulatory s ubunit.