Endogenously expressed Trp1 is involved in store-mediated Ca2+ entry by conformational coupling in human platelets

Physical interaction between transient receptor potential (Trp) channels and inositol 1,4,5-trisphosphate receptors (IP(3)Rs) has been presented as a candidate mechanism for the activation of store-mediated Ca2+ entry. The role of a human homologue of Drosophila transient receptor potential channel, hTrp1, in the conduction of store-mediated Ca2+ entry was examined in human platelets. Incubation of platelets with a specific antibody, which recognizes the extracellular amino acid sequence 557-571 of hTrp1, inhibited both store depletion-induced Ca2+ and Mn2+ entry in a concentration-dependent manner. Stimulation of platelets with the physiological agonist thrombin activated coupling between the IP3 receptor type II and endogenously expressed hTrp1. This event was reversed by refilling of the internal Ca2+ stores but maintained after removal of the agonist if the stores were not allowed to refill. Inhibition of IP3 recycling using Li+ or inhibition of IP(3)Rs with xestospongin C or treatment with jasplakinolide, to stabilize the cortical actin filament network, abolished thrombin-induced coupling between hTrp1 and IP3R type II. Incubation with the anti-hTrp1 antibody inhibited thrombin-evoked Ca2+ entry without affecting Ca2+ release from intracellular stores. These results provide evidence for the involvement of hTrp1 in the activation of store-mediated Ca2+ entry by coupling to IP3R type II in normal human cells.