Nucleotide leakage from platelets in artificial media: prevention by albumin and other macromolecules and relation to ADP-induced platelet aggregation.

Leakage of ATP and ADP from gel filtered rabbit platelets has been investigated. It was found that upon suspending the platelets in a non-protein medium, accumulation of ADP and ATP externally to the platelets took place. Addition of albumin to the suspending medium resulted in rapid disappearance of extra-platelet nucleotides. It could also be demonstrated that the leakage of adenine nucleotides from the platelets was due specifically to the change of media and not to mechanical damage of the platelets during the isolation procedure. Several other macromolecules like fibrinogen, β- and γ-globulins, and dextran sulphate had a moderately protective effect on the platelets, but not to the same extent as albumin. The raised extra-platelet concentrations of ATP and ADP found in non-protein media was shown to be related to the decrease of the reactivity of the platelets to ADP. Fibrinogen potentiated ADP-induced aggregation of gel filtered platelets, but only when the platelets were suspended in a medium containing albumin.