Summary
1. The respiratory activity of human blood platelets has been investigated quantitatively. It is not affected by the normal procedures for isolating washed platelets from plasma, nor by the absence of plasma proteins. Optimal synthetic media for platelet respiration are described; they contain EDTA in a suitable buffered system. The addition of thrombin always causes a depression of oxygen uptake. No direct relationship exists between respiratory activity and clot retraction. Respiration may even be inhibited without affecting clot retraction.
2. Under the conditions of clot retraction and with glucose present, a remarkable stimulation of the glycolytic activity is observed. This increase in the production of lactic acid and of glucose consumption is of short duration and is followed by a total breakdown of glycolysis. The maximum of glycolytic activity coincides with the onset of clot retraction initiated by the addition thrombin. Inhibition of glycolysis leads to a total suppression of glucose utilisation and to impaired retraction activity.
3. In glucose containing systems and with thrombin the ATP-level in platelets closely follows the pattern of glycolytic activity, i.e. a sharp initial rise, followed by a rapid decay of the triphosphate. Without glucose the addition of thrombin to suitably buffered platelets causes a rapid decrease of ATP.
4. The retraction activity of the blood platelets is found to be directly dependent on their ATP-level. The synthesis of ATP during the process of clot retraction is effected by the glycolytic system, provided glucose is present as a substrate
5. Most probably the major part of the ATP consumed during the retraction period is active in the contraction of an actomyosin-like protein contained in the platelets.
