Coassembly of Trp1 and Trp3 proteins generates diacylglycerol- and Ca2+-sensitive cation channels

To analyze the functional consequences of coassembly of transient receptor potential 1 (Trp1) and Trp3 channel proteins, we characterized membrane conductances and divalent cation entry derived by separate overexpression and by coexpression of both Trp isoforms. Trp1 expression generated a 1-oleoyl-2-acetyl-sn-glycerol (OAG)-activated conductance that was detectable only in Ca(2+)-free extracellular solution. Trp3 expression gave rise to an OAG-activated conductance that was suppressed but clearly detectable at physiological Ca(2+) concentrations. Coexpression of both species resulted in a constitutively active, OAG-sensitive conductance, which exhibited distinctive cation selectivity and high sensitivity to inhibition by intracellular Ca(2+). Trp1-expressing cells displayed only modest carbachol-induced Ca(2+) entry and lacked OAG-induced Sr(2+) entry, whereas Trp3-expressing cells responded to both agents with a substantial divalent cation entry. Coexpression of Trp1 plus Trp3 suppressed carbachol-induced Ca(2+) entry compared with Trp3 expression and abolished OAG-induced Sr(2+) entry signals. We concluded that coassembly of Trp1 and Trp3 resulted in the formation of oligomeric Trp channels that are subject to regulation by phospholipase C and Ca(2+). The distinguished Ca(2+) sensitivity of these Trp1/Trp3 hetero-oligomers appeared to limit Trp-mediated Ca(2+) signals and may be of importance for negative feedback control of Trp function in mammalian cells.