Summary
The ADP-induced release of 3H-serotonin from human platelets in heparinized platelet rich plasma is markedly stimulated
by the addition of sodium citrate. The aggregation and release that is induced by
collagen is less affected by citrate. Data is presented that supports the view that
the effects of citrate on both ADP-and collagen-induced release are largely via alteration
of the concentration of ionized calcium in plasma.
Collagen can induce release of 3H-serotonin via extracellular calcium-independent and -dependent mechanisms. The possibility
that the calcium-dependent mechanism is aggregation-dependent and that the calcium
is required for platelet aggregation rather than directly involved in the release
reaction is discussed.
