Epinephrine induces Ca2+ uptake in human blood platelets.

Human blood platelets isolated by albumin density gradient centrifugation take up Ca2+ during 10(-6)M epinephrine-induced primary aggregation but not during 10(-6)M ADP-induced primary aggregation. Platelet uptake of Ca2+ is dose-dependent over a range of 10(-7) to 10(-5) M epinephrine. Antagonism of the platelet alpha-receptor by phentolamine (10(-6)M) results in inhibition of both epinephrine-stimulated Ca2+ uptake and aggregation. The Ca2+ antagonist verapamil (50 micro M) blocks Ca2+ uptake and epinephrine-induced aggregation, but not ADP-induced aggregation. The verapamil inhibition of aggregation is reduced on Ca2+ addition. These results suggest that epinephrine acts to stimulate primary platelet aggregation through a specific receptor interaction that results in a selective increase in platelet membrane permeability to Ca2+.