Ca2+-activated K+ channels underlying the impaired acetylcholine-induced vasodilation in 2K-1C hypertensive rats

We tested the hypothesis that an abnormal function of K+ channels in vascular smooth muscle cells plays a key role in the impaired acetylcholine (ACh) vasodilation in aortas from two kidney-one clip (2K-1C) hypertensive rats and further investigated the K+ channel subtype involved in this altered response. ACh-induced endothelium-dependent relaxation was assessed in aortic rings from 2K-1C and normotensive two kidney (2K) rats. Glibenclamide, an ATP-sensitive K+ channel blocker, did not inhibit ACh-induced relaxation in aortic rings from 2K or 2K-1C rats. The voltage-dependent K+ channels inhibitor 4-aminopyridine attenuated ACh-induced relaxation in both groups. Charybdotoxin and iberiotoxin, blockers of Ca2+-sensitive (K-Ca) and large-conductance K-Ca (BKCa) channels, respectively, reduced ACh-induced relaxation in aortic rings from 2K rats without affecting this response in those from 2K-1C rats, abolishing the differences between groups. ACh-induced relaxation in vessels from both 2K and 2K-1C rats was unaffected by apamin, a small-conductance K., blocker. NS1619 [1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one], an activator of K-Ca, induced a smaller vasodilation in endothelium-denuded aortic rings from 2K-1C rats compared with those from 2K rats. Iberiotoxin reduced sodium nitroprusside-induced relaxation in endothelium-denuded aortic rings from 2K without affecting this response in those from 2K-1C rats. The inhibition of Na+,K+-ATPase with ouabain had no effects on ACh-induced relaxation in aortic rings from 2K-1C or 2K rats. These data indicate that a deficient functional activity of BKCa channels plays a key role in the impaired ACh vasodilation in aortas from 2K-1C rats.