Vasoregulation by isoform‐selective coupling of TRPC3 channels to IP 3 receptors in smooth muscle cells

Inositol 1,4,5‐trisphophate (IP 3 ) stimulates vasoconstriction independently of intracellular Ca 2+ release via IP 3 receptor (IP 3 R) and canonical transient receptor potential (TRPC) channel activation, but signaling mechanisms mediating this effect are unclear. Here, we studied the mechanisms by which IP 3 Rs stimulate TRPC channels in cerebral artery myocytes. Immuno‐FRET microscopy in myocytes 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. Endothelin‐1 (ET‐1), a PLC‐coupled receptor agonist, elevated the immuno‐FRET signal between IP 3 R1 and TRPC3, but not between IP 3 R1 and TRPC6 or TRPM4. IP 3 R1 co‐immunoprecipitated with TRPC3, but not with TRPC6. An antibody targeting TRPC3 channels and TRPC3 channel knockdown using shRNA inhibited IP 3 ‐induced non‐selective cation current (I Cat ) activation, whereas an antibody to TRPC6 and TRPC6 channel knockdown had no effect. Biotinylation indicated that ET‐1 did not alter total or plasma membrane‐localized TRPC3. RT‐PCR demonstrated that a calmodulin and IP 3 R binding (CIRB) domain is present on the C‐terminus of both TRPC3 and TRPC6 channels. A peptide corresponding to the IP 3 R region that can interact with TRPC channels activated I Cat . A CIRB domain peptide attenuated IP 3 ‐ and ET‐1‐induced I Cat activation and vasoconstriction. These data indicate that IP 3 stimulates direct coupling between IP 3 R1 and membrane‐resident TRPC3 channels in arterial myocytes, leading to I Cat activation and vasoconstriction. Data also indicate that close spatial proximity between IP 3 R1 and TRPC3 establishes this isoform‐selective functional interaction.