The dual effects of Ca2+ on binding of the glycolytic enzymes, phosphofructokinase and aldolase, to muscle cytoskeleton.

We show here that in rat diaphragm muscle, a short time of incubation with the Ca(2+)-ionophore A23187 induced an increase in cytoskeleton-bound phosphofructokinase (EC 2.7.1.11) and aldolase (EC 4.1.2.13), whereas a longer period of incubation, which causes a pathological rise in intracellular Ca2+, induced a decrease in bound enzymes. Lactate concentration correlated with both phases of Ca2+ action on the binding of the enzymes. The increase in cytoskeleton-bound enzymes could be prevented by treatment with the calmodulin antagonists trifluoperazine or CGS 9343B (a novel, potent, and selective inhibitor of calmodulin activity). These results suggest that calmodulin is involved in the Ca(2+)-induced binding of the enzymes to muscle cytoskeleton.