Abstract

ATP-sensitive K⁺ (K_ATP) channel openers are vasodilators that activate both plasma membrane and mitochondrial K_ATP channels. Here, we investigated the molecular mechanisms by which diazoxide and pinacidil induce vasodilation by studying diameter regulation of wild-type [SUR2(+/+)] and sulfonylurea receptor (SUR) 2-deficient [SUR2(-/-)] mouse myogenic mesenteric arteries. Ryanodine (10 μM), a ryanodine-sensitive Ca²⁺ release (RyR) channel blocker; iberiotoxin (100 nM), a large-conductance Ca²⁺-activated K⁺ (K_Ca) channel blocker; 4-aminopyridine (4-AP; 1 mM), a voltage-gated K⁺ (K_V) channel blocker; manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP; 100 μM), an antioxidant; and a combination of ryanodine and 4-AP reduced diazoxide (100 μM)-induced dilation in pressurized (60 mm Hg) SUR2(+/+) arteries by 45 to 77%. In contrast, these inhibitors did not alter pinacidil (5 μM)-induced dilation in SUR2(+/+) arteries. Reverse transcription-polymerase chain reaction indicated that SUR2B was the only SUR isoform expressed in SUR2(+/+) mesenteric artery smooth muscle cells, whereas SURs were absent in SUR2(-/-) cells. In SUR2(-/-) arteries, pinacidil-induced vasodilation was ∼10% of that in SUR2(+/+) arteries, whereas diazoxide-induced vasodilation was similar in SUR2(+/+) and SUR2(-/-) arteries. Atpenin (1 μM), a selective electron transport chain (ETC) complex II inhibitor, dilated arteries similarly to diazoxide, and this effect was attenuated by MnTMPyP and ryanodine + 4-AP. Atpenin also attenuated diazoxide-, but not pinacidil-induced vasodilation. In summary, data indicate that pinacidil-induced vasodilation requires SUR2B, whereas diazoxide-induced vasodilation does not require SURs. Rather, diazoxide-induced vasodilation involves ETC_II inhibition; a smooth muscle cell-reactive oxygen species elevation; and RyR, K_Ca, and K_V channel activation. These data indicate that K_ATP channel openers regulate arterial diameter via SUR-dependent and -independent pathways.