Acute hypoxia induces vasodilation and increases coronary blood flow by activating inward rectifier K+ channels

We examined the effects of acute hypoxia on vascular tone and coronary blood flow (CBF) in rabbit coronary arteries. In the pressurized arterial preparation of small arteries (< 100 mu m) and the Langendorff-perfused rabbit hearts, hypoxia induced coronary vasodilation and increased CBF in the presence of glibenclamide (K-ATP channel blocker), Rp-8-Br-PET-cGMPs [cyclic guanosine monophosphate (cGMP)-dependent protein kinase inhibitor, Rp-cGMPs], and methionyl transfer RNA synthetase (MRS) 1334 (adenosine A(3) receptor inhibitor); these increases were inhibited by the inward rectifier K+ (Kir) channel inhibitor, Ba2+. These effects were blocked by the adenylyl cyclase inhibitor SQ 22536 and by the cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) inhibitors Rp-8-CPT-cAMPs (Rp-cAMPs) and KT 5720. However, cGMP-dependent protein kinase was not involved in the hypoxia-induced increases of the vascular diameter and CBF. In summary, our results suggest that acute hypoxia can induce the opening of Kir channels in coronary artery that has small diameter (< 100 mu m) by activating the cAMP and PKA signalling pathway, which could contribute to vasodilation and, therefore, increased CBF.