Opening of Small and Intermediate Calcium-Activated Potassium Channels Induces Relaxation Mainly Mediated by Nitric-Oxide Release in Large Arteries and Endothelium- Derived Hyperpolarizing Factor in Small Arteries from Rat

ABSTRACT This study was designed to investigate whether calcium-activated potassium channels of small (SK Ca or K Ca 2) and intermediate (IK Ca or K Ca 3.1) conductance activated by 6,7-dichloro-1H-indole-2,3-dione 3-oxime (NS309) are involved in both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in large and small rat mesenteric arteries. Segments of rat superior and small mesenteric arteries were mounted in myographs for functional studies. NO was recorded using NO microsensors. SK Ca and IK Ca channel currents and mRNA expression were investigated in human umbilical vein endothelial cells (HUVECs), and calcium concentrations were investigated in both HUVECs and mesenteric arterial endothelial cells. In both superior (ϳ1093 m) and small mesenteric (ϳ300 m) arteries, NS309 evoked endothelium-and concentration-dependent relaxations. In superior mesenteric arteries, NS309 relaxations and NO release were inhibited by both N G ,N G -asymmetric dimethyl-L-arginine (ADMA) (300 M), an inhibitor of NO synthase, and apamin (0.5 M) plus 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) (1 M), blockers of SK Ca and IK Ca channels, respectively. In small mesenteric arteries, NS309 relaxations were reduced slightly by ADMA, whereas apamin plus an IK Ca channel blocker almost abolished relaxation. Iberiotoxin did not change NS309 relaxation. HUVECs expressed mRNA for SK Ca and IK Ca channels, and NS309 induced increases in calcium, outward current, and NO release that were blocked by apamin and TRAM-34 or charybdotoxin. These findings suggest that opening of SK Ca and IK Ca channels leads to endothelium-dependent relaxation that is mediated mainly by NO in large mesenteric arteries and by EDHF-type relaxation in small mesenteric arteries. NS309-induced calcium influx appears to contribute to the formation of NO

Opening of small and intermediate calcium-activated potassium channels induce relaxation mainly mediated by NO release in large arteries and EDHF in small arteries from rat Number of text pages: 22 Number of tables: 0 Number of figures: 5 Number of refere

Abstract This study was designed to investigate whether calcium-activated potassium channels of small (SK Ca or K Ca 2) and intermediate (IK Ca or K Ca 3.1) conductance activated by NS309 are involved in both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) type relaxation in large and small rat mesenteric arteries. Segments of rat superior and small mesenteric arteries were mounted in myographs for functional studies. NO was recorded using NO microsensors. SK Ca and IK Ca channel-currents, and mRNA expression were investigated in human umbilical vein endothelial cells (HUVECs), and calcium concentrations both in HUVEC and mesenteric arterial endothelial cells. In both superior (~1093 µm) and small mesenteric (~300 µm) arteries, NS309, evoked endothelium-and concentration-dependent relaxations. In superior mesenteric arteries, NS309 relaxations and NO release were inhibited both by asymmetric dimethylarginine (ADMA, 300 µM), an inhibitor of NO synthase, and by apamin (0.5 µM) plus TRAM 34 (1 µM), blockers of SK Ca and IK Ca channels, respectively. In small mesenteric arteries, NS309 relaxations were slightly reduced by ADMA, whereas apamin plus an IK Ca channel blocker almost abolished the relaxation. Iberiotoxin did not change NS309 relaxation. HUVECs expressed mRNA for SK Ca and IK Ca channels, and NS309 induced increases in calcium, outward current, and NO release that was blocked by apamin and TRAM 34 or charybdotoxin. These findings suggest that opening of SK Ca and IK Ca channels leads to endothelium-dependent relaxation that is mainly mediated by NO in large mesenteric arteries and by EDHF-type relaxation in small mesenteric arteries. NS309-induced calcium influx appears to contribute to formation of NO. JPET #179242