Purpose : Nicorandil opens adenosine triphosphate-sensitive potassium (KATP)
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 KATP 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 KATP channels in cultured
rat aortic smooth muscle cells. Furthermore, we also investigated whether intracellular
MgADP could modulate ketamine inhibition. Results : Nicorandil significantly activated
KATP channel activity, whereas this channel activity was completely blocked by glibenclamide,
a specific KATP channel blocker. Ketamine racemate inhibited the nicorandil induced
KATP channel activity (IC50=34 1M, n=14), but S-(+)-ketamine was less potent than ketamine
racemate in blocking nicorandil induced KATP channel activities (IC50=226 7M,
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 KATP channel activities.
Conclusions : Our results indicate that ketamine inhibits nicorandil induced KATP channel
activities in a dose dependent and stereoselective manner. Furthermore, increase of
intracellularMgADP attenuates the inhibitory potency of ketamine racemate
