Objective: To evaluate the role of potassium channels in the regulation of coronary hemodynamics in experimental hypercholesterolemia. Background: Potassium (K + ) channels play an important role in coronary vasoregulation. It has previously been demonstrated that experimental hypercholesterolemia is associated with altered coronary vasomotion; however, the role of K + channels in modulating coronary blood flow in this pathophysiologic state has not been evaluated. Methods and results: Pinacidil (group 1, n=5) at 2 μg/kg per min, glibenclamide (group 2, n=5), or N-monomethyl-l-arginine (LNMMA) (group 3, n=4) at 50 μg/kg per min were infused into the left anterior descending artery of pigs prior to and following 10 weeks of 2% cholesterol diet. After 10 weeks of cholesterol feeding, intracoronary pinacidil resulted in a significant increase in coronary blood flow (CBF) and coronary artery diameter (CAD) compared to the normolipidemic state (111+/-10 versus 59+/-12%, and 6+/-1.1 versus 2.7+/-1.0%, respectively, P<0.05 for both comparisons), whereas intracoronary glibenclamide resulted in a significant decrease in CBF and CAD compared to the normolipidemic state (-17+/-5 versus 5+/-6%, and -0.8+/-1.4 versus 3.6+/-1.6%, respectively, P<0.05 for both comparisons). The effect of intracoronary LNMMA on CBF and CAD was significantly attenuated after 10 weeks of cholesterol feeding as compared to the normolipidemic state (-47+/-5.4 versus -0.8+/-6.8%, and -19.4+/-5.7 versus -2.3+/-3.3%, respectively, P<0.05 for both comparisons). Furthermore, pretreatment with intracoronary LNMMA did not alter the CBF response to pinacidil in normal pigs (group 4, n=4) (57.4+/-19 versus 59+/-12%, P=NS). Conclusions: The current study demonstrates an enhanced effect of coronary K + channel modulation and confirms the attenuated basal NO activity previously reported in experimental hypercholesterolemia. Acute withdrawal of basal NO activity alone, however, does not explain the enhanced effect of coronary K + channel modulation. These findings underscore the importance of the K + channel pathway in the regulation of coronary vasomotor tone in pathophysiologic states.