Isoform-Selective Physical Coupling of TRPC3 Channels to IP3 Receptors in Smooth Muscle Cells Regulates Arterial Contractility

Rationale: Inositol 1,4,5-trisphosphate (IP3)-induced vasoconstriction can occur independently of intracellular Ca2+ release and via IP3 receptor (IP3R) and canonical transient receptor potential (TRPC) channel activation, but functional signaling mechanisms mediating this effect are unclear. Objectives: Study mechanisms by which IP(3)Rs stimulate TRPC channels in myocytes of resistance-size cerebral arteries. Methods and Results: Immunofluorescence resonance energy transfer (immuno-FRET) microscopy using isoform-selective antibodies indicated that endogenous type 1 IP(3)Rs (IP(3)R1) are in close spatial proximity to TRPC3, but distant from TRPC6 or TRPM4 channels in arterial myocytes. Endothelin-1 (ET-1), a phospholipase C-coupled receptor agonist, elevated immuno-FRET between IP(3)R1 and TRPC3, but not between IP(3)R1 and TRPC6 or TRPM4. TRPC3, but not TRPC6, coimmunoprecipitated with IP(3)R1. TRPC3 and TRPC6 antibodies selectively inhibited recombinant channels, but only the TRPC3 antibody blocked IP3-induced nonselective cation current (I-Cat) in myocytes. TRPC3 knockdown attenuated immuno-FRET between IP(3)R1 and TRPC3, IP3-induced ICat activation, and ET-1 and IP3-induced vasoconstriction, whereas TRPC6 channel knockdown had no effect. ET-1 did not alter total or plasma membrane-localized TRPC3, as determined using surface biotinylation. RT-PCR demonstrated that C-terminal calmodulin and IP3R binding (CIRB) domains are present in myocyte TRPC3 and TRPC6 channels. A peptide corresponding to the IP3R N-terminal region that can interact with TRPC channels activated I-Cat. A TRPC3 CIRB domain peptide attenuated IP3- and ET-1-induced I-Cat activation and vasoconstriction. Conclusions: IP3 stimulates direct coupling between IP(3)R1 and membrane-resident TRPC3 channels in arterial myocytes, leading to I-Cat activation and vasoconstriction. Close spatial proximity between IP(3)R1 and TRPC3 establishes this isoform-selective functional interaction. (Circ Res. 2010;106:1603-1612.)