Increased GPVI-mediated collagen-induced platelet aggregation and ERK2 activation with transgenic platelets.

(A) Light transmission (%) recordings in apyrase (1 U/mL)–treated washed WT or TG mouse platelets stimulated with collagen (1-2 μg/mL) or convulxin (0.03 μg/mL). (B) Platelet aggregations were induced with collagen (1 μg/mL) in the absence of apyrase (2 curves on the left). The other curves represent collagen-induced platelet aggregations performed in the presence of apyrase after 1-minute preincubation with αβ-meATP (1 μM) or with the MEK1/2 inhibitor U0126 (1 μM), as indicated. Arrows depict the time of collagen application. (C) Western blot analyses of ERK2 phosphorylation (P-ERK2) evoked by collagen in WT or TG apyrase-treated platelets. For TG, data from 2 independent platelet pools are shown. Samples were analyzed 3 minutes after collagen addition. Blockade of collagen-induced ERK2 phosphorylation with U0126 (1 μM) is shown for WT platelets in parallel with its effect on WT platelet aggregation (panel B). Data are representative of at least 3 independent experiments performed in duplicate on platelets from WT and TG mice.