FUNCTIONAL-PROPERTIES OF CARDIAC L-TYPE CALCIUM CHANNELS TRANSIENTLY EXPRESSED IN HEK293 CELLS - ROLE OF ALPHA-(1) AND BETA SUBUNITS

The cardiac dihydropyridine-sensitive calcium channel was transiently expressed in HEK293 cells by transfecting the rabbit cardiac calcium c hannel alpha 1 subunit (alpha(1C)) alone or in combination with the ra bbit calcium channel beta subunit cloned from skeletal muscle. Transfe ction with alpha(1C) alone leads to the expression of inward, voltage- activated, calcium or barium currents that exhibit dihydropyridine sen sitivity and voltage- as well as calcium-dependent inactivation. Coexp ression of the skeletal muscle beta subunit increases current density and the number of high-affinity dihyhropyridine binding sites and also affects the macroscopic kinetics of the current. Recombinant alpha(1C )beta channels exhibit a slowing of activation and a faster inactivati on rate when either calcium or barium carries the charge. Our data sug gest that both an increase in the number of channels as well as modula tory effects on gating underlie the modifications observed upon beta s ubunit coexpression.