CA2+-DRIVEN [H-3] ARACHIDONATE RELEASE IN ELECTROPERMEABILIZED HUMAN PLATELETS SHOWS AN ABSOLUTE REQUIREMENT FOR MGATP2-

Addition of micromolar Ca2+ to electropermeabilized human platelets which had been pre-labelled with [H-3]arachidonate causes release of H-3 only when millimolar concentrations of a nucleoside triphosphate, e.g. ATP, are present in the incubation medium. Addition of millimolar Ca2+ in the absence of ATP, or preincubation with ATP before addition of micromolar Ca2+, fails to cause a significant increase in H-3 release. Purine nucleotides are more effective than pyrimidine nucleotides in activating Ca2+ -driven H-3 release. This activation does not appear to involve phosphate transfer, since metabolically stable analogues of ATP, e.g. the beta-gamma-imido analogue, are effective in promoting H-3 release.