Protein Components of the Purified Sodium Channel from Rat Skeletal Muscle Sarcolemma

Abstract

Sensitive detection systems were used to study the protein components of the Na channel purified from rat skeletal muscle sarcolemma. This functional, purified Na channel contains at least 3 subunits on 7-20% gradient sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis: a large glycoprotein which migrates anomalously in the high-MW range, a 45,000 MW polypeptide and a 3rd protein often seen as a doublet at 38,000. The large glycoprotein runs as a diffuse band and stains very poorly with Coomassie blue, but is adequately visualized the silver staining or iodination followed by autoradiography. This glycoprotein exhibits anomalous electrophoretic behavior in SDS-polyacrylamide gels. The apparent MW of the center of the band varies from .apprx. 230,000 on 13% acrylamide gels to .apprx. 130,000 on 5% gels; on 7-20% gradient gels a value of 160,000 is found. Plots of relative migration vs. gel concentration suggest an unusually high apparent free solution mobility. Lectin binding to purified channel peptides separated by gel electrophoresis indicates that the large glycoprotein is the only subunit that binds either concanavalin A or wheat germ agglutinin, and this component has high binding capacity for both lectins. The smaller channel components run consistently at 45,000 and 38,000 MW in a variety of gel systems and do not appear to be glycosylated.