The modulatory role of myosin light chain phosphorylation in human platelet activation.

Myosin 20 K-Da light chain phosphorylation in human platelets was found to be catalyzed by MLCK in the early phase during collagen activation. The effect of newly synthesized selective inhibitor of MLCK, ML-9, on collagen induced platelet activation was investigated. ML-9 delayed the time course of the myosin 20 K-Da light chain phosphorylation, sequentially led to a delay in aggregation, secretion and phosphorylation of the 40K-Da peptide, in a dose-dependent fashion. It is proposed that the MLCK catalyzed phosphorylation of myosin 20 K-Da light chain may be an initial response and if so may influence the sequent reactions in the activation of platelets with collagen.