Increased ATP release and Ca²⁺mobilization in platelets from GRK6^−/−mice. (A) ATP release for platelets stimulated with AYPGKF, or (B) CVX at the concentrations indicated (N = 3). (C) Isolated mouse platelets were suspended in Tyrode buffer without Ca²⁺ and loaded with fura-2 AM (10 μM). The platelets were then washed and resuspended in Tyrode buffer with no extracellular Ca²⁺ and 0.5 μM EGTA. Changes in fura-2 AM fluorescence were detected with a JASCO FP-8300 spectrofluorometer, exciting at 340 and 380 nm, and measuring emission at 510 nm. Platelets were stimulated with AYPGKF, ADP, U46619, or CVX at the concentrations indicated in the absence of extracellular Ca²⁺. Representative measurements are shown. (D) The results of 3 experiments (mean ± SEM) are summarized. ***Significant difference (P ≤ .05).