Cell surface changes accompanying myoblast differentiation

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Abstract
Myoblasts are mononucleated cells and associated with differentation undergo cell fusion and become multinucleated. The current studies have examined cell surface dynamic changes of Concanavalin A lectin receptor mobility and the role of hormones in modulating myoblast differentiation. A uniform distribution of Con-A receptors is observed in undifferentiated cells when reacted with Con-A at 37°C. Cells from differentiating cultures or fully differentiated myotubes reacted similarly at 37°C show a significant redistribution of Con-A into patches, “caps,” and endocytic vesicles containing Con-A. If undifferentiated and differentiated cells are first prefixed with glutaraldehyde then reacted with Con-A continuous distribution of Con-A is seen across the cell surface. This suggests redistribution of Con-A and its receptors occurs in differentiated cells reacted with lectin at 37°C. It is further shown that insulin (10 μg/ml) significantly enhances myoblast differentiation but that this occurs after an apparent stimulation of proliferation. In contrast to insulin, dexamethasone (10 μM and 100 μM) profoundly inhibits myoblast differentiation while having different effects on proliferation; 10 μM dex stimulates cell growth while 100 μM dex suppresses cell proliferation. Lastly, an extracellular filamentous matirix which binds Con-A is observed at the ultrastructural level in high density cultures. No significant redistribution of Con-A is observed on this matrix in distinction to the redistribution observed on the cell membrane in differentiated cells.