Muscle‐derived factors induce proliferation and astrocytic phenotypic expression in C‐6 glial cells

Previous studies from our laboratory have shown that C‐6 glial cells in culture express astrocytic phentoypes with increasing cell passage. Early passage glial cells have been shown to respond to various factors by expressing either astrocytic or oligodendrocytic phenotype. In view of the numerous reports on the trophic effects of muscle‐derived factors on spinal cord neurons, we examined the effect of muscle‐dervied factors on C‐6 glial cells from both early and late passages. Soluble factors were obtained from either leg (LME) or breast (BME) muscle from 15‐day‐old chick embryos by homogenization followed by high velocity centrifugation. Both LME‐ and BME‐derived factors triggered the proliferation and differentiation of early passage glial cells as assessed by cell number and glutamine synthetase activity, respectively. Late passage glial cells responded to muscle‐derved factors with enhanced proliferation and only with a slight increase in glutamine synthetase activity. These findings indicate that glial cells of both early and late passages respond to signals produced by muscle cells.