A monoclonal antibody to the β subunit of the skeletal muscle dihydropyridine receptor immunoprecipitates the brain ω-conotoxin GVIA receptor

Abstract

Antibodies against the subunits of the dihydropyridine-sensitive L-type calcium channel of skeletal muscle were tested for their ability to immunoprecipitate the high affinity (Kd = 0.13 nM) 125I-ω-conotoxin GVIA receptor from rabbit brain membranes. Monoclonal antibody VD21 against the β subunit of the dihydropyridine receptor from skeletal muscle specifically immunoprecipitated up to 86% of the 125I-ω-conotoxin receptor solubilized from brain membranes whereas specific antibodies against the α1, α2, and γ subunits did not precipitate the brain receptor. Purified skeletal muscle dihydropyridine receptor inhibited the immunoprecipitation of the brain ω-conotoxin receptor by monoclonal antibody VD21. The dihydropyridine receptor from rabbit brain membranes was also precipitated by monoclonal antibody VD21. However, neither the neuronal ryanodine receptor nor the sodium channel was precipitated by monoclonal antibody VD21. The ω-conotoxin receptor immunoprecipitated by monoclonal antibody VD21 showed high affinity 125I-ω-conotoxin binding, which was inhibited by unlabeled ω-conotoxin and by CaCl2 but not by nitrendipine or by diltiazem. An antibody against the β subunit of the skeletal muscle dihydropyridine receptor stained 58- and 78-kDa proteins on immunoblot of the ω-conotoxin receptor, partially purified through heparin-agarose chromatography and VD21-Sepharose chromatography. These results suggest that the brain ω-conotoxin-sensitive calcium channel contains a component homologous to the β subunit of the dihydropyridine-sensitive calcium channel of skeletal muscle and brain.