Ca(v) 3.2 T-type calcium channel regulates mouse platelet activation and arterial thrombosis.

BACKGROUND: Ca(v) 3.2 is a T-type calcium channel that causes low-threshold exocytosis. T-type calcium channel blockers reduce platelet granule exocytosis and aggregation. However, studies of the T-type calcium channel in platelets are lacking. OBJECTIVE: To examine the expression and role of Ca(v) 3.2 in platelet function. METHODS: Global Ca(v) 3.2(-/-) and platelet-specific Ca(v) 3.2(-/-) mice and littermate controls were used for this study. Western blot analysis was used to detect the presence of Ca(v) 3.2 and activation of the calcium-responsive protein extracellular signal-regulated kinase (ERK). Fura-2 dye was used to assess platelet calcium. Flow cytometry and light transmission aggregometry were used to evaluate platelet activation markers and aggregation, respectively. FeCl(3) -induced thrombosis and a microfluidic flow device were used to assess in vivo and ex vivo thrombosis, respectively. RESULTS: Ca(v) 3.2 was expressed in mouse platelets. As compared with wild-type controls, Ca(v) 3.2(-/-) mouse platelets showed reduced calcium influx. Similarly, treatment with the T-type calcium channel inhibitor Ni(2+) decreased the calcium influx in wild-type platelets. As compared with controls, both Ca(v) 3.2(-/-) and Ni(2+) -treated wild-type platelets showed reduced activation of ERK. ATP release, P-selectin exposure, and α(IIb) β3 activation were reduced in Ca(v) 3.2(-/-) and Ni(2+) -treated wild-type platelets, as was platelet aggregation. On in vivo and ex vivo thrombosis assay, Cav3.2 deletion caused delayed thrombus formation. However, tail bleeding assay showed intact hemostasis. CONCLUSION: These results suggest that Ca(v) 3.2 is required for the optimal activation of platelets.