The role of the KATP channel in functional and reactive myocardial hyperemia

To evaluate the role of the KATP channel in regulating coronary tonus in response to increases in myocardial oxygen consumption, and reactive hyperemia following ischemia, coronary blood flow was measured with glibenclamide, a KATP channel blocker (50μmol/l ic.) and pinacidil, a KATP channel opener, (10μmol/l ic.)The following interventions were applied in the control and during intracoronary infusions of glibenclamide alone or glibenclamide plus pinacidil: 1) intravenous infusion of isoproterenol (0.125μg/kg/min), 2) aortic constriction to raise the mean aortic pressure by 30%.The slope of the regression line of coronary conductance of myocardial oxygen consumption was significantly decreased with glibenclamide (p<0.05), but returned to the baseline with pinacidil, both during isoproterenol infusion and aortic constriction. Reactive hyperemia following a 20-sec coronary occlusion was also attennuated with glibenclamide and recovered with pinacidil.These findings suggest that the KATP channel regulates coronary artery tonus during the increase in myocardial oxygen consumption and transient myocardial ischemia.