TRPC1 associates with BK_Ca channel to form a signal complex in vascular smooth muscle cells

TRPC1 (transient receptor potential canonical 1) is a Ca ²⁺-permeable cation channel involved in diverse physiological function. TRPC1 may associate with other proteins to form a signaling complex, which is crucial for channel function. In the present study, we investigated the interaction between TRPC1 and large conductance Ca²⁺-sensitive K⁺ channel (BK_Ca). With the use of potentiometric fluorescence dye DiBAC₄(3), we found that store-operated Ca ²⁺ influx resulted in membrane hyperpolarization of vascular smooth muscle cells (VSMCs). The hyperpolarization was inhibited by an anti-TRPC1 blocking antibody T1E3 and 2 BK_Ca channel blockers, charybdotoxin and iberiotoxin. These data were confirmed by sharp microelectrode measurement of membrane potential in VSMCs of intact arteries. Furthermore, T1E3 treatment markedly enhanced the membrane depolarization and contraction of VSMCs in response to several contractile agonists including phenylephrine, endothelin-1, and U-46619. In coimmunoprecipitation experiments, an antibody against BK _Ca α-subunit [BK_Ca(α)] could pull down TRPC1, and moreover an anti-TRPC1 antibody could reciprocally pull down BK _Ca(α). Double-labeling immunocytochemistry showed that TRPC1 and BK_Ca were colocalized in the same subcellular regions, mainly on the plasma membrane, in VSMCs. These data suggest that, TRPC1 physically associates with BK_Ca in VSMCs and that Ca influx through TRPC1 activates BK_Ca to induce membrane hyperpolarization. The hyperpolarizing effect of TRPC1-BK_Ca coupling could serve to reduce agonist-induced membrane depolarization, thereby preventing excessive contraction of VSMCs to contractile agonists.