ROLE OF ATP-SENSITIVE POTASSIUM CHANNELS IN CORONARY MICROVASCULAR AUTOREGULATORY RESPONSES

The purpose of the present study was to test the hypothesis that ATP-sensitive potassium channels mediate autoregulatory vasodilatation of coronary arterioles in vivo. Experiments were performed in 23 open-chest anesthetized dogs. Coronary arterial microvascular diameters were directly measured with fluorescence microangiography using an intravital microscope and stroboscopic epi-illumination synchronized to the cardiac cycle. A mild coronary stenosis (perfusion pressure = 60 mm Hg), a critical coronary stenosis (perfusion pressure = 40 mm Hg), and complete coronary artery occlusion were produced with an occluder around the left anterior descending coronary artery in the presence or absence of glibenclamide (10(-5) M, topically), which inhibits ATP-sensitive potassium channels, or of vehicle. During topical application of vehicle (0.01% dimethyl sulfoxide), there was dilatation of small (< 100-mu-m diameter) arterioles during reductions in perfusion pressure (percent change in diameter: 6.7 +/- 1.5%, 11.7 +/- 3.5%, and 10.4 +/- 5.1% during mild stenosis, critical stenosis, and complete occlusion, respectively). In the presence of glibenclamide, arteriolar dilatations during coronary stenoses and occlusions were abolished. Glibenclamide did not affect responses of arterioles > 100-mu-m. Glibenclamide did not alter microvascular responses to nitroprusside. These data suggest that ATP-sensitive potassium channels play an important role in determining the coronary microvascular response to reductions in perfusion pressure.