Levels of enzymes of energy metabolism are controlled by activity of cultured rat myotubes.

We have investigated the effects of inhibiting the spontaneous activity of cultured rat myotubes on several representative enzymes of glycolytic and oxidative metabolism. The results presented demonstrate that contractile activity in the absence of nerves can regulate the amounts of these enzymes and indicate that muscle activity may partially control development of the metabolic types of muscle fibers. Control muscle cells have relatively high levels of glycolytic enzymes and low oxidative enzymes and metabolically most closely resemble fast glycolytic fibers. The divalent cation ionophore A23187 caused enzyme levels of the cultured cells to change towards those found in tonically contracting skeletal muscle fibers in vivo. The evidence presented suggests that calcium may mediate certain of the effects associated with muscle contraction on enzymes of energy metabolism.