ADENINE-NUCLEOTIDE METABOLISM OF BLOOD-PLATELETS .9. TIME COURSE OF SECRETION AND CHANGES IN ENERGY-METABOLISM IN THROMBIN-TREATED PLATELETS

Changes in the energy metabolism of washed human platelets were compared with the kinetics of secretion induced by thrombin (5 units/ml). A 50% decrease in the level of metabolic ATP (3H-labeled), which was essentially complete in 30 s, was matched in rate by adenine nucleotide secretion from storage in dense granules. Incubation of platelets with antimycin before thrombin addition increased the rate of fall in metabolic ATP but did not affect the rate of adenine nucleotide secretion. .beta.-N-Acetylglucosaminidase secretion, which was slower than adenine nucleotide secretion in control platelets, was noticeably inhibited by antimycin, confirming previous reports that different regulatory mechanisms exist for dense and .alpha.-granule secretion. The rates of rephosphorylation of metabolic ADP to ATP via glycolysis and oxidative phosphorylation were estimated by measuring lactate production and O2 consumption in resting and thrombin-stimulated platelets and compared to the level of metabolic ATP (9-10 nmol/mg of platelet protein in the resting state). The rate of ATP production was stimulated at least 2-fold from 12 nmol-24 nmol/min per mg within seconds of thrombin addition. This increased rate was maintained over the observed period of 5 min although the level of metabolic ATP had decreased to 4-5 nmol/mg within 30 s; the turnover of the remaining metabolic ATP increased 4-fold over the resting state although the actual stimulation of energy production was only 2-fold.