A Calcium Channel from the Presynaptic Nerve Terminal of the Narke japonica Electric Organ Contains a Non-N-Type α2δ Subunit

Abstract

A monoclonal antibody (MCC-1) that recognizes the alpha 2 delta subunit complex of L-type calcium channels from rabbit skeletal muscle membranes partially inhibited the evoked release of acetylcholine from synaptosomes isolated from the electric organ of the marine electric ray, Narke japonica. Digitonin extracts of synaptosomal plasma membranes were subjected to immunoaffinity column chromatography on MCC-1-Sepharose. The purified fraction contained a 170-kDa protein that reacts with MCC-1 and dissociates into smaller polypeptides under reducing conditions. In addition, immunoblotting analysis revealed the existence of syntaxin in the purified fraction, suggesting that the calcium channel forms a complex with syntaxin. However, MCC-1 did not immunoprecipitate an omega-conotoxin GVIA-binding protein. These findings indicate that the 170-kDa protein may be the alpha 2 delta subunit of a calcium channel that is distinct from the omega-conotoxin GVIA-sensitive N-type calcium channel and partially responsible for the calcium influx that triggers the evoked release of acetylcholine.