Expression of Functional Receptor-coupled TRPC3 Channels in DT40 Triple Receptor InsP₃ knockout Cells

The TRPC3 channel, an intensively studied member of the widely expressed transient receptor potential (TRP) family, is a Ca²⁺-conducting channel activated in response to phospholipase C-coupled receptors. Despite scrutiny, the receptor-induced mechanism to activate TRPC3 channels remains unclear. Evidence indicates TRPC3 channels interact directly with intracellular inositol 1,4,5-trisphosphate receptors (InsP₃Rs) and that channel activation is mediated through coupling to InsP₃Rs. TRPC3 channels were expressed in DT40 chicken B lymphocytes in which all three InsP ₃R genes were deleted (DT40InsP₃R-k/o). Endogenous B-cell receptors (BCR) coupled through Syk kinase to phospholipase C-γ (PLC-γ) activated the expressed TRPC3 channels in both DT40w/t and DT40InsP₃R-k/o cells. The diacylglycerol (DAG) analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) also activated TRPC3 channels independently of InsP₃Rs. BCR-induced TRPC3 activation was blocked by the PLC enzymic inhibitor, U-73122, and also blocked by wortmannin-induced PLC substrate depletion. Neither U-73122 nor wortmannin modified either OAG-induced TRPC3 activation or store-operated channel activation in DT40 cells. Cotransfection of cells with both G protein-coupled M5 muscarinic receptors and TRPC3 channels resulted in successful M5 coupling to open TRPC3 channels mediated by PLC-β. We conclude that TRPC3 channels are activated independently of InsP₃Rs through DAG production resulting from receptor-mediated activation of either PLC-γ or PLC-β.