Ultrastructural localization of alpha-, beta- and gamma-sarcoglycan and their mutual relation, and their relation to dystrophin, beta-dystroglycan and beta-spectrin in normal skeletal myofiber.

Ultrastructural localization of alpha-, beta- and gamma-sarcoglycan and their mutual relation, and their relation to dystrophin, beta-dystroglycan and beta-spectrin were investigated in normal skeletal myofibers. Single-immunogold labeling electron microscopy showed that the signals of rabbit and sheep polyclonal antibodies against the synthetic peptide of the cytoplasmic domain of alpha-, beta or gamma-sarcoglycan were present along the inside surface of muscle plasma membrane and at the sarcoplasmic side of plasma membrane invaginations and vesicular structures in subsarcolemmal areas. These localizations were similar to that of dystrophin, beta-dystroglycan and beta-spectrin. Double-immunogold labeling disclosed the close association of alpha-, beta- and gamma-sarcoglycan each other and alpha-, beta-, gamma-sarcoglycan with dystrophin or beta-dystroglycan, and this was confirmed by statistical analysis. Monoclonal antibody against the extracellular domain of alpha-sarcoglycan was used with above-mentioned polyclonal anti-beta- and -gamma-sarcoglycan antibodies for triple-immunogold labeling, in which signals of alpha-sarcoglycan localized at the outer surface of muscle plasmalemma and those of beta- and gamma-sarcoglycans were present at the inside surface of plasma membrane. The triple immunolabeling showed an occasional closely associated presence of the three signals for alpha-, beta-and gamma-sarcoglycans, and a more frequent association for two signals out of alpha-, beta- and gamma-sarcoglycans. This study demonstrated that alpha-, beta- and gamma-sarcoglycan are closely located to one another and to dystrophin and beta-dystroglycan at the muscle plasma membrane.