Platelet NK1 receptors couple to G_q G proteins. Washed human platelets (A,C) or platelets loaded with [³H] arachidonic acid (D) were stimulated with EKA/B (5 μM), and mouse platelets were taken from Gα_q-deficient mice or their litter-match controls and stimulated with SP (10 μM, B), and in the presence of the Gα_q inhibitor YM-254890 (A,D) or PLC inhibitor U73122 or its inactive analog U73343 (C). The results represent platelet aggregation as a percent of the respective vehicle control (A,C), mouse platelet aggregation assessed by single-cell number is displayed as a percentage of basal cell number (B), and arachidonic acid release presented as the percentage of total [³H] arachidonic acid taken up into the platelet minus basal release (D). All data represent means plus or minus SEM. *P < .05; **P < .01; ***P < .001; n = 3 (A,C,D) or 6 (B).