Ion channels in the regulation of platelet migration

Platelets have been shown to migrate and thus to invade the vascular wall. Platelet migration is stimulated by SDF-1. In other cell types, migration is dependent on Ca²⁺ entry via Ca²⁺ channels. Ca²⁺ influx is sensitive to cell membrane potential which is maintained by K⁺ channel activity and/or Cl⁻ channel activity. The present study explored the role of ion channels in the regulation of SDF-1 induced migration. Platelets were isolated from human volunteers as well as from gene targeted mice lacking the Ca²⁺ activated K⁺ channel SK4 (sk4^−/−) and their wild type littermates (sk4^+/+). According to confocal microscopy human platelets expressed the Ca²⁺ channel Orai1 and the Ca²⁺-activated K⁺ channel K_Ca3.1 (SK4). SDF-1 (100 ng/ml) stimulated migration in human platelets, an effect blunted by Orai1 inhibitors 2-aminoethoxydiphenyl borate 2-APB (10 μM) and SKF-96365 (10 μM), by unspecific K⁺ channel inhibitor TEA (30 mM), by SK4 specific K⁺ channel blocker clotrimazole (10 μM), but not by Cl⁻ channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid NPPB (100 μM). Significant stimulation of migration by SDF-1 was further observed in sk4^+/+ platelets but was virtually absent in sk4^−/− platelets. In conclusion, platelet migration requires activity of the Ca²⁺ channel Orai1 and of the Ca²⁺ activated K⁺ channel SK4, but not of NPPB-sensitive Cl⁻ channels.