Phosphatidylinositol 4,5-bisphosphate enhances store-operated calcium entry through hTRPC6 channel in human platelets

Phosphatidylinositol 4,5-bisphosphate (PIP(2)) is a versatile regulator of TRP channels. We report that inclusion of a PIP(2) analogue, PIP(2) 1,2-dioctanoyl, does not induce non-capacitative Ca(2+) entry per se but enhanced Ca(2+) entry stimulated either by thrombin or by selective depletion of the Ca(2+) stores in platelets, the dense tubular system, using 10 nM TG, and the acidic stores, using 20 mu M 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ). Reduction of PIP(2) levels by blocking PIP(2) resynthesis with Li(+) or introducing a monoclonal anti-PIP(2) antibody, or sequestering PIP(2) using poly-lysine, attenuated Ca(2+) entry induced by thrombin, TG and TBHQ, and reduced thrombin-evoked, but not TG- or TBHQ-induced, Ca(2+) release from the stores. Incubation with the anti-hTRPC1 antibody did not alter the stimulation of Ca(2+) entry by PIP2, whilst introduction of anti-hTRPC6 antibody directed towards the C-terminus of hTRPC6 reduced Ca(2+) and Mn(2+) entry induced by thrombin, TG or TBHQ, and abolished the stimulation of Ca(2+) entry by PIP(2). The anti-hTRPC6 antibody, but not the anti-hTRPC1 antibody or PIP(2), reduced non-capacitative Ca(2+) entry by the DAG analogue I-oleoyl-2-acetyl-sn-glycerol. In summary, hTRPC6 plays a role both in store-operated and in non-capacitative Ca(2+) entry. PIP(2) enhances store-operated Ca(2+) entry in human platelets, most probably by stimulation of hTRPC6 channels. (C) 2007 Elsevier B.V. All rights reserved.