Calcium channel subtypes in rat brain: biochemical characterization of the high-affinity receptors for ω-conopeptides SNX-230 (synthetic MVIIC), SNX-183 (SVIB), and SNX-111 (MVIIA)

Abstract

High-threshold voltage-sensitive calcium channels of the N-type, L-type, and P-type have been distinguished in the mammalian CNS predominantly on the basis of their sensitivity to selective antagonists. Matching them with genes identified by molecular cloning is an ongoing undertaking. Whereas L-type channels are characterize by their sensitivity to dihydropyridines and P-type channels by sensitivity to the funnel-web spider toxin AgaIVA, the N-type channel has been shown to be recognized by the ω-conopeptides GVIA and MVIIA. Recently, two new members of the family of ω-conopeptides-MVIIC from the marine snail Conus magus and SVIB from Conus strains-have been described. Binding and electrophysiological data suggest that these two peptides, in addition to interacting with N-type calcium channels, interact with a widely distributed receptor in neuronal membranes that is distinct from N-type channels. In this report we demonstrate through biochemical and pharmacological differentiation at individual receptor pelypeptide resolution, by affinity cross-linking, SDS-PAGE, and autoradiography, that SNX-230 (synthetic MVIIC) binds with high affinity to a calcium channel α₁ subunit distinct from the high-affinity α₁ target of SNX-111 (synthetic MVIIA). SNX-183 (synthetic SVIB) interacts with both α₁ subunits with lower affinity. Whereas the α₁ subunit recognized with high affinity by MVIIA corresponds to the N-type channel, the other represents a novel calcium channel distinct from N-, L-, and perhaps P-type channels.