Purpose: Nicorandil opens adenosine triphosphate-sensitive potassium (K
ATP) channels in the cardiovascular system and is being increasingly used for the treatment of angina pectoris. In the present study, we tested whether intravenous anesthetic agent ketamine affected nicorandil-induced native vascular K
ATP channel activation. Methods: We used excised inside-out patch clamp configurations to investigate the direct effects of ketamine racemate and S-(+)-ketamine on the activities of K
ATP channels in cultured rat aortic smooth muscle cells. Furthermore, we also investigated whether intracellular MgADP could modulate ketamine inhibition. Results: Nicorandil significantly activated K
ATP channel activity, whereas this channel activity was completely blocked by glibenclamide, a specific K
ATP channel blocker. Ketamine racemate inhibited the nicorandil induced K
ATP channel activity (
IC50=34±1 µM, n=14), but S-(+)-ketamine was less potent than ketamine racemate in blocking nicorandil induced K
ATP channel activities (
IC50=226±7 µM, n=10). Application of MgADP to the intracellular side of the channel was able to decrease the inhibitory potency of ketamine racemate on nicorandil induced K
ATP channel activities. Conclusions: Our results indicate that ketamine inhibits nicorandil induced K
ATP channel activities in a dose dependent and stereoselective manner. Furthermore, increase of intracellular MgADP attenuates the inhibitory potency of ketamine racemate. J. Med. Invest. 57: 237-244, August, 2010
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