Epoxyeicosatrienoic acids act through TRPV4-TRPC1-KCa1.1 complex to induce smooth muscle membrane hyperpolarization and relaxation in human internal mammary arteries

Human left internal mammary arteries (LIMAs) are commonly used as donor grafts for coronary bypass surgery. Previous reports suggested that 11,12-epoxyeicosatrienoic acid (11,12-EET) is an important endothelial-derived hyperpolarizing factor (EDHF) in human LIMAs and that EETs act through large conductance Ca2 +-activated K+ channels (KCa1.1) to induce smooth muscle cell hyperpolarization and relaxation in these tissues. In this study, we aimed to explore the role of vanilloid transient receptor potential channel 4 (TRPV4) and canonical transient receptor potential channel 1 (TRPC1) channels in the EET-induced smooth muscle hyperpolarization and vascular relaxation in human LIMAs. Co-immunoprecipitation studies demonstrated that TRPV4, TRPC1, and KCa1.1 physically interacted with each other to form a complex. Sharp microelectrode and vascular tension studies demonstrated that 11,12-EET (300 nmol/L) and 4α-phorbol 12,13-didecanoate (5 μmol/L) were able to induce smooth muscle membrane hyperpolarization and vascular relaxation in isolated human LIMA segments. The hyperpolarizing and relaxant effects were markedly reduced by treatments that could suppress the expression/activity of TRPV4, TRPC1, or KCa1.1. With the use of human embryonic kidney 293 cells that over-expressed with TRPV4, TRPC1 and KCa1.1, we found that TRPC1 is the linker through which TRPV4 and KCa1.1(α) can interact. The present study revealed that 11,12-EET targets the TRPV4-TRPC1-KCa1.1 complex to induce smooth muscle cell hyperpolarization and vascular relaxation in human LIMAs. This finding provides novel mechanistic insights for the EET action in human LIMAs.