Effects of CyPB on Ca²⁺ flux and phosphorylation of myosin light chains (P-20) and pleckstrin (P-47) in platelets. Ca²⁺ mobilization, measured in Fluo-3–loaded platelets, was analyzed after the addition of CyPB (100 nmol/L normal (A) or Ca²⁺-depleted buffer (B). Changes in fluorescence, reflecting changes in cytosolic Ca²⁺ concentration, were monitored by flow cytofluorimetry. Tracings are representative of 3 distinct experiments conducted with platelets from separate individuals. The arrows indicate addition of the ligand. Platelet response to CyPB (100 nmol/L) was also analyzed in terms of variations of P-20 and P-47 protein phosphorylation (C). Reactions were stopped at the indicated times and the variations in the intensity of serine phosphorylation of P-20 (•) and P-47 (○) were analyzed. Zero time results were obtained without addition of the ligand. Data are calculated as the percentage of intensity at indicated times relative to that at time zero, and expressed as mean values ± SEM from 3 separate experiments conducted with platelets from different donors.