Involvement of Energy Metabolism in Platelet Responses

Shape change, aggregation, arachidonate liberation and secretion of the contents of dense granules or α-granules and of acid hydrolases are distinct in vitro responses by platelets to physiological stimuli. They may participate in in vivo platelet functions and are abolished at a certain reduction of ATP availability in vitro which is specific for each response. The ATP level in platelets respond normally. Hence, with normal ATP turnover the responses are not dependent on the ATP level at the moment of induction When ATP turnover is shut off by addition of 2-deoxyglucose and glucono-δ-lactone to antimycin A-treated platelets, the ATP level falls rapidly and the initial rate of aggregation and the extent of dense granule secretion are proportional to the ATP level at the moment of induction. Thus, these responses do not depend on ATP generation during execution and available ATP appears to be preferentially utilized to drive the responses. Myosin light chain phosphorylation precedes secretion, indicating ATP usage in contractile processes. A large proportion of ATP may bEt used to maintain actin in a non-polymerized state in restiug platelets. Since actin filaments appear during platelet stimulation, ATP may also be used in the unstimulated platelet to Keep these cells responsive (prevent actin polymerization).