Platelet adhesion, shape change, and aggregation: rapid initiation and signal transduction events.

Blood platelets are essential for hemostasis, and knowledge of their function is important for understanding both normal and pathologic situations. A number of approaches have been used to evaluate platelet adhesion, aggregation, and secretion, and within the last 10 years much interest has been directed to the biochemical mechanisms and signal transduction events occurring during these various phases of function. New information has come from development of technologies to evaluate the changes occurring immediately after platelet activation and consistent with the speed needed for hemostasis in the arterial circulation. Use of rapid flow and mixing technologies as seen in quenched-flow, continuous-flow, and stopped-flow devices has revealed that platelet aggregation, shape change, adhesion, and secretion begin within 1 s and may be nearly complete by 5 s. Biochemical changes such as in protein phosphorylation, calcium release, and phospholipid hydrolysis are clearly evident in hundreds of milliseconds. Therefore, it is necessary to understand these early events in signal transduction and to assess alterations that may occur in diseases such as diabetes.