STABLE COEXPRESSION OF CALCIUM-CHANNEL ALPHA(1), BETA AND ALPHA(2/DELTA) SUBUNITS IN A SOMATIC-CELL LINE

1. The high-voltage-activated L-type calcium channel is a multi-protein complex of alpha1, alpha2/delta, beta and gamma subunits. The alpha1 subunit contains the voltage-dependent calcium-conducting pore. Chinese hamster ovary (CHO) cells were stably transfected with the complementary DNA of the alpha1, beta and alpha2/delta subunit. These subunits were not detected in wild-type CHO cells. 2. The alpha (CaCh2b) subunit itself directed the expression of functional calcium channels which bound calcium channel blockers and showed voltage-dependent activation and inactivation. 3. The co-expression of the alpha1 subunit with the beta subunit (CaB1 gene) enhanced the density of the dihydropyridine binding sites 2- to 3-fold and increased dihydropyridine-sensitive barium inward currents (I(Ba)) up to 3.5-fold from -13.3 muA/cm2 (alpha1 subunit) to -46.7 muA/cm2 (alpha1 and beta subunits). 4. Co-expression of the beta subunit did not change the sensitivity of I(Ba) towards dihydropyridines, but accelerated current activation and inactivation and shifted the half-maximal steady-state activation and inactivation to slightly more hyperpolarizing potentials. 5. The co-expression of the alpha1/delta subunit together with alpha and beta subunits accelerated the inactivation kinetics of the channel without a major effect on the other parameters. 6. These results indicate that the beta and alpha2/delta subunit interact with the alpha1 subunit and modulate thereby the properties of the alpha1 subunit-dependent inward current.