Inhibition of platelet aggregation by low concentrations of sodium fluoride. Significance of the intracellular calcium ion concentration.

: Sodium fluoride activates platelets but its mechanism of action has not yet been completely identified. We examined the effect of a low concentration of sodium fluoride (which could not cause aggregation) on thrombin-induced changes in the intracellular calcium ion concentration ([Ca2+]i). In the presence of 1 mM extracellular Ca2+, preincubation with a low concentration of sodium fluoride decreased the peak of the thrombin-induced elevation of [Ca2+]i, when measured with aequorin. When [Ca2+] was measured using fura-2, preincubation caused no marked changes in its peak, but the later changes that were thought to mainly reflect extracellular Ca2+ influx were inhibited. The inhibitory mechanism of sodium fluoride appears to depend on reducing extracellular Ca2+ influx. Aequorin appears to reflect [Ca2+]i near the cell membrane and is thus easily affected by the extracellular Ca2+ influx.