Antibody localization studies of the M-line in striated muscle

Abstract

An investigation of species and organ specificity of M-protein was conducted with antibodies produced to M-protein extracted from porcine skeletal muscle with solutions containing 0.25 M sucrose. Light microscopic observations with fluorescein isothiocyanate (FITC) labeled antibody and electron microscopic observations with unlabeled antibody revealed that anti-M bound only to the M-line of both fresh and glycerinated porcine skeletal and cardiac muscle. Antibody binding was eliminated by extraction of KCl-washed myofibrils with sucrose solutions. Fluorescent staining with FITC-anti-M was eliminated by prior treatment with unlabeled anti-M serum but was not prevented by prior treatment with nonimmune rabbit serum. M-line-staining antibodies were removed from antiserum by absorption with M-protein but not by absorption with actin, tropomyosin, or α-actinin. Double diffusion of anti-M against M-protein resulted in a strong precipitin reaction, which did not occur with myosin, tropomyosin, α-actinin, actin, or phosphorylase. Antibody induced by porcine M-protein bound strongly to the M-line of mouse, rabbit, and human skeletal muscle and weakly to the M-line of frog skeletal muscle.