Two monoclonal antibodies raised against brain synaptic membranes immunoprecipitated significant fractions of the brain omega-conotoxin receptor (probable omega-conotoxin-sensitive calcium channels) solubilized with digitonin. These antibodies recognized different proteins of 36 kDa and 28 kDa, respectively. Immunoblot analysis of fractions obtained by sucrose gradient centrifugation suggested that these two proteins were not subunits of the omega-conotoxin receptor but were bound to it. These proteins were found to be conserved at least from an amphibian to mammals, and to be present in the nervous system and adrenal medulla among the tissues examined.
