Epinephrine-induced Ca²⁺ influx in vascular endothelial cells is mediated by CNGA2 channels

Epinephrine, through its action on β-adrenoceptors, may induce endothelium-dependent vascular dilation, and this action is partly mediated by a cytosolic Ca²⁺ ([Ca²⁺]_i) change in endothelial cells. In the present study, we explored the molecular identity of the channels that mediate epinephrine-induced endothelial Ca²⁺ influx and subsequent vascular relaxation. Patch clamp recorded an epinephrine- and cAMP-activated cation current in the primary cultured bovine aortic endothelial cells (BAECs) and H5V endothelial cells. L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated channels, diminished this cation current. Furthermore, this cation current was greatly reduced by a CNGA2-specific siRNA in H5V cells. With the use of fluorescent Ca²⁺ dye, it was found that epinephrine and isoprenaline, a β-adrenoceptor agonist, induced endothelial Ca²⁺ influx in the presence of bradykinin. This Ca²⁺ influx was inhibited by L-cis-diltiazem and LY-83583, and by a β₂-adrenoceptor antagonist ICI-118551. CNGA2-specific siRNA also diminished this Ca²⁺ influx in H5V cells. Furthermore, L-cis-diltiazem and LY-83583 inhibited the endothelial Ca²⁺ influx in isolated mouse aortic strips. L-cis-diltiazem also markedly reduced the endothelium-dependent vascular dilation to isoprenaline in isolated mouse aortic segments. In summary, CNG channels, CNGA2 in particular, mediate β-adrenoceptor agonist-induced endothelial Ca²⁺ influx and subsequent vascular dilation.