Surface labeling studies of normal and dystrophic myogenic cells in culture

Surface protein topographies of cultured normal and genetically dystrophic embryonic chick breast muscle cells and fibroblasts were compared by external labeling and size distribution analysis by sodium dodecyl sulfate-polyacrylamide gradient slab gel electrophoresis. Four labeling techniques were evaluated and all were found to be specific for the cell surface. Using radioiodination of tyrosine residues and periodate-barotritide labeling of sialic acid residues, no reproducible abnormalities could be detected in any of the dystrophic cell types--fibroblasts, fusion-inhibited differentiated myoblasts, and multinucleated differentiated myotubes. However, comparison of 3-day-old cultures of normal fusion-inhibited differentiated myoblasts with fused myotubes revealed that increased iodination of protein classes with nominal molecular weights of 230,000 and 88,000 was evident in the myoblasts. In addition, large structural differences were detected between differentiated myoblasts and myogenic cells grown in the presence of phorbol 12-myristate 13-acetate, a potent tumor promoter and reversible inhibitor of myogenic differentiation.