Citrate metabolism by human platelets

As part of a study on the utilization of substrates by platelets in defined media the metabolism of citrate was measured, since citrate is a common anticoagulant of nearly all such media, and is also an intermediate of oxidative metabolism. Human platelets transferred from plasma to an artificial medium by gel filtration, were incubated with [14C]citrate at 22 degrees C and labelled carbon dioxide produced was measured during short-term incubations of 2 h. Citrate (1 mM) was oxidized to carbon dioxide at low (0.3 nmol per 10(9) platelets h-1) but significant rates, and the oxidation was decreased by the presence of an alternative substrate (acetate) in the medium. There was, however, no significant conversion of citrate to glycogen. It was calculated that under normal storage conditions of platelet concentrates for transfusion purposes, the amount of citrate used cannot decrease citrate concentrations sufficiently to bring about platelet activation.