The primary structures of human neuronal α1, α2, and β subunits of a voltage-dependent Ca2+ channel were deduced by characterizing cDNAs. The α1 subunit (α1D) directs the recombinant expression of a dihydropyridine-sensitive L-type Ca2+ channel when coexpressed with the β (β2) and the α2 (α2b) subunits in Xenopus oocytes. The recombinant channel is also reversibly blocked by 10-15 μM ω-conotoxin. Expression of the α1D subunit alone, or coexpression with the α2b subunit, did not elicit functional Ca2+ channel activity. Thus, the β2 subunit appears to serve an obligatory function, whereas the α2b subunit appears to play an accessory role that potentiates expression of the channel. The primary transcripts encoding the α1D, α2, and β subunits are differentially processed. At least two forms of neuronal α1D were identified. Different forms of α2 and β transcripts were also identified in CNS, skeletal muscle, and aorta tissues.
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