CALCIUM-CHANNEL SUBTYPES IN RAT-BRAIN - BIOCHEMICAL-CHARACTERIZATION OF THE HIGH-AFFINITY RECEPTORS FOR OMEGA-CONOPEPTIDES SNX-230 (SYNTHETIC MVIIC), SNX-183 (SVIB), AND SNX-111 (MVIIA)

High-threshold voltage-sensitive calcium channels of the N-type, L-typ e, and P-type have been distinguished in the mammalian CNS predominant ly on the basis of their sensitivity to selective antagonists. Matchin g them with genes identified by molecular cloning is an ongoing undert aking. Whereas L-type channels are characterized by their sensitivity to dihydropyridines and P-type channels by sensitivity to the funnel-w eb spider toxin AgaIVA, the N-type channel has been shown to be recogn ized by the omega-conopeptides GVIA and MVIIA. Recently, two new membe rs of the family of omega-conopeptides-MVIIC from the marine snail Con us magus and SVIB from Conus striatus-have been described. Binding and electrophysiological data suggest that these two peptides, in additio n to interacting with N-type calcium channels, interact with a widely distributed receptor in neuronal membranes that is distinct from N-typ e channels. In this report we demonstrate through biochemical and phar macological differentiation at individual receptor polypeptide resolut ion, by affinity cross-linking, SDS-PAGE, and autoradiography, that SN X-230 (synthetic MVIIC) binds with high affinity to a calcium channel al subunit distinct from the high-affinity alpha1 target of SNX-111 (s ynthetic MVIIA). SNX- 183 (synthetic SVIB) interacts with both alpha1 subunits with lower affinity. Whereas the alpha1 subunit recognized wi th 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. (C) 1994 Academic Press, Inc.