Oxygen consumption of human blood platelets. I. Effect of thrombin

The effect of thrombin on the oxygen consumption of washed human platelets was measured polarographically with the Clark oxygen electrode. The average basal respiratory rate was 18 plus or minus 1.6 (mean plus or minus S.E.) natoms oxygen per min per 10-9 platelets. Thrombin (1.9 units/ml) caused a 4-13-fold increase in the rate of oxygen consumption (138 plus or minus 14 (mean plus or minus S.E.) natoms oxygen per min per 10-9 platelets). The thrombin-stimulated increase of oxygen consumption was transient, lasting from 1 to 1.5 min before returning to the respiratory rate observed before the thrombin addition. Release of platelet constituents appeared to precede the stimulation of oxygen consumption. These results may provide a basis for explaining the discrepancy in the literature concerning the effects of thrombin on platelet respiration.

Oxygen consumption of human blood platelets. II. Effect of inhibitors on thrombin-induced oxygen burst

The effect of selected inhibitors on the thrombin-stimulated burst and the basal oxygen consumption of washed human platelets were investigated and compared with inhibition of the release reaction. Cyanide (0.2 mM) caused complete inhibition of the basal respiration, but only 15% inhibition of the thrombin-stimulated burst of oxygen consumption. Similar differential inhibitory effects were observed with oligomycin, antimycin, rotenone and N-ethylmaleimide. Prostaglandin E1 (0.03 mM) and acetylsalicylic acid (0.8 mM) had little effect on basal respiration, but inhibited the thrombin-stimulated burst of oxygen consumption. N-Ethylmaleimide (0.4 mM) inhibited the release of calcium from platelets by 90%, while prostaglandin E1, acetylsalicylic acid and the above mitochondrial inhibitors caused no more than 30% inhibition of the release reaction. Our results provide evidence that basal respiration and a portion of the thrombin-stimulated burst of oxygen consumption are involved in respiratory chain phosphorylation, and that this component of the thrombin-stimulated burst may be coupled to the maintenance of the release reaction.