Endogenously Expressed Trp1 Is Involved in Store-mediated Ca super(2+) Entry by Conformational Coupling in Human Platelets

Physical interaction between transient receptor potential (Trp) channels and inositol 1,4,5-trisphosphate receptors (IP sub(3)Rs) has been presented as a candidate mechanism for the activation of store-mediated Ca super(2+) entry. The role of a human homologue of Drosophila transient receptor potential channel, hTrp1, in the conduction of store-mediated Ca super(2+) 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 Ca super(2+) and Mn super(2+) entry in a concentration-dependent manner. Stimulation of platelets with the physiological agonist thrombin activated coupling between the IP sub(3) receptor type II and endogenously expressed hTrp1. This event was reversed by refilling of the internal Ca super(2+) stores but maintained after removal of the agonist if the stores were not allowed to refill. Inhibition of IP sub(3) recycling using Li super(+) or inhibition of IP sub(3)Rs with xestospongin C or treatment with jasplakinolide, to stabilize the cortical actin filament network, abolished thrombin-induced coupling between hTrp1 and IP sub(3)R type II. Incubation with the anti-hTrp1 antibody inhibited thrombin-evoked Ca super(2+) entry without affecting Ca super(2+) release from intracellular stores. These results provide evidence for the involvement of hTrp1 in the activation of store-mediated Ca super(2+) entry by coupling to IP sub(3)R type II in normal human cells.