Functional properties of cardiac L-type calcium channels transiently expressed in HEK293 cells: Roles of α1 and β subunits

The cardiac dihydropyridine-sensitive calcium channel was transiently expressed in HEK293 cells by transfecting the rabbit cardiac calcium channel a, subunit (α_1C) alone or in combination with the rabbit calcium channel β subunit cloned from skeletal muscle. Transfection with α_1C alone leads to the expression of inward, voltage-activated, calcium or barium currents that exhibit dihydropyridine sensitivity and voltage- as well as calcium-dependent inactivation. Coexpression of the skeletal muscle β subunit increases current density and the number of high-affinity dihydropyridine binding sites and also affects the macroscopic kinetics of the current. Recombinant α_1Cβ channels exhibit a slowing of activation and a faster inactivation rate when either calcium or barium carries the charge. Our data suggest that both an increase in the number of channels as well as modulatory effects on gating underlie the modifications observed upon β subunit coexpression.