Metabolic energy is required in human platelets at any stage during optical aggregation and secretion.

The relationship between metabolic energy and platelet aggregation and secretion was investigated by sudden exhaustion of the cell energy content after these platelet responses had been initiated. In normal platelets, optical aggregation was at any stage susceptible to energy exhaustion, whereas single platelet disappearance and secretion were hardly affected. Prelowering the platelet energy content, while preserving the adenylate energy charge, made both optical aggregation and the secretion from dense, alpha- and acid hydrolase-containing granules susceptible to energy exhaustion, but single platelet disappearance was not affected. Complete arrest of secretion occurred when the energy content had fallen below 3-3.5 mumol ATP equivalents (ATPeq)/10(11) platelets, while optical aggregation was interrupted below 2-2.5 mumol ATPeq/10(11) platelets. At any stage of optical aggregation and the three secretion responses, the dependence on energy remained the same, indicating a tight coupling between these functions and metabolic energy, which held during the entire responses.