Effects of antimycin and 2 deoxyglucose on adenine nucleotides in human platelets. Role of metabolic adenosine triphosphate in primary aggregation, secondary aggregation and shape change of platelets

Abstract

Human platelet rich plasma prelabelled with [3H]adenine was incubated at 37°C with antimycin A and 2 deoxy D glucose. Variations in the amounts of ATP, ADP and P(i) and in the radioactivity of ATP, ADP, AMP, IMP, hypoxanthine + inosine and adenine were determined during incubation. Adrenaline and ADP induced platelet aggregation and the ADP induced shape change of the platelets were determined concurrently. 2 Deoxyglucose caused conversion of [3H]ATP to [3H]hypoxanthine + inosine. The rate of this conversion by addition of antimycin, which had no effect alone. At maximal ATP hypoxanthine converion rates, the IMP radioactivity remained at values tenfold higher than control, whereas [3H]ADP and [3H]AMP radioactivity gave cariation typical for product/substrates in consecutive reactions. The specific radioactivity of ethanol soluble platelet ATP decreased during incubation to less than one tenth of its original value. The amounts and radioactivity of ethanol insoluble ADP did not vary during incubation with the metabolic inhibitors. The rate of ADP and adrenaline induced primary aggregation decreased as the amount of radioactive ATP declined, and complete inhibition of aggregation was obtained at a certain ATP concentration (metabolic ATP threshold). This threshold decreased with increasing concentration of inducer ADP. Secondary platelet aggregation (release reaction) had a metabolic ATP threshold markedly higher than that of primary aggregation. Shape change was gradually inhibited as the ATP radioactivity decreased, and had a metabolic ATP threshold distinctly lower than that of primary aggregation, and which decreased with increasing concentration of ADP. A small but distinct fraction of [3H]ATP disappeared rapidly during the combined shape change aggregation process induced in ADP in platelets incubated with metabolic inhibitors, whereas no ATP disappearance occurred during aggregation in their absence.