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Institut für Pharmacokologie und Toxikologie, Technische Universität München, Germany.
1. The high-voltage-activated L-type calcium channel is a multi-protein complex of alpha 1, alpha 2/delta, beta and gamma subunits. The alpha 1 subunit contains the voltage-dependent calcium-conducting pore. Chinese hamster ovary (CHO) cells were stably transfected with the complementary DNA of the alpha 1, beta and alpha 2/delta subunits. These subunits were not detected in wild-type CHO cells. 2. The alpha 1 (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 alpha 1 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 (IBa) up to 3.5-fold from -13.3 microA/cm2 (alpha 1 subunit) to -46.7 microA/cm2 (alpha 1 and beta subunits). 4. Co-expression of the beta subunit did not change the sensitivity of IBa 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 alpha 2/delta subunit together with alpha 1 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 alpha 2/delta subunit interact with the alpha 1 subunit and modulate thereby the properties of the alpha 1 subunit-dependent inward current.
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