The involvement of Ca2+ and myosin light chain kinase in collagen-induced platelet activation.

In this study we have used several complementary biochemical and immunological techniques to examine the involvement of Ca2+ and myosin light chain kinase in collagen-induced platelet activation. Our results indicate that collagen stimulates a rapid influx of external Ca2+ (within the first 1-5 min of treatment) which is followed by phosphorylation of myosin light chains (within 10 min of treatment) and granule secretion (within 15 min of treatment). In addition, we have found that certain Ca2+ channel entry blockers (e.g. nifedipine and bepridil) or calmodulin antagonists (e.g. W-7) specifically inhibit collagen-induced Ca2+ influx, myosin light chain phosphorylation and subsequent granule secretion. These data suggest that Ca2+/calmodulin-dependent myosin light chain kinase-mediated myosin light chain phosphorylation is necessary for regulating the actomyosin-related contractility required for normal platelet function.