Complex regulation of the TRPC3, 6 and 7 channel subfamily by diacylglycerol and phosphatidylinositol-4,5-bisphosphate.

TRPC3, 6 and 7 channels constitute a subgroup of non-selective, calcium-permeable cation channels within the TRP superfamily that are activated by products of phospholipase C-mediated breakdown of phosphatidylinositol-4,5-bisphosphate (PIP(2)). A number of ion channels, including other members of the TRP superfamily, are regulated directly by PIP(2). However, there is little information on the regulation of the TRPC channel subfamily by PIP(2). Pretreatment of TRPC7-expressing cells with a drug that blocks the synthesis of polyphosphoinositides inhibited the ability of the synthetic diacylglycerol, oleyl-acetyl glycerol, to activate TRPC7. In excised patches, TRPC7 channels were robustly activated by application of PIP(2) or ATP, but not by inositol 1,4,5-trisphosphate. Similar results were obtained with TRPC6 and TRPC3, although the effects of PIP(2) were somewhat less and with TRPC3 there was no significant effect of ATP. In the cell-attached configuration, TRPC7 channels could be activated by the synthetic diacylglycerol analog, oleyl-acetyl glycerol. However, this lipid mediator did not activate TRPC7 channels in excised patches. In addition, channel activation by PIP(2) in excised patches was significantly greater than that observed with oleyl-acetyl glycerol in the cell-attached configuration. These findings reveal complex regulation of TRPC channels by lipid mediators. The results also reveal for the first time direct activation by PIP(2) of members of the TRPC ion channel subfamily.