The effects of a newly synthesized potassium channel opener, KR-30816((-)(nitro-2-hydroxymethyl-2-methy-2H-1-benzopyran-4-y1)pyridine oxide) on the action potential of papillary muscles of guinea pigs and the ATP-sensitive potassium channel current(I_KATP) of single ventricular muscle cells of rats were examined to make clear its action mechanism of the K_ATPchannel.

We used the conventional microelectrode and the excised inside-out patch configuration.

KR-30816 caused a shortening of the action potential duration in dose-dependent manner, which was inhibited by glibenclamide(3µM). Before run-down of the K⁺channel, KR-30816 activated the cardiac ATP-sensitive K⁺channel only in the presence of ATP and shifted the dose-response relation curve between [ATP]_iand the channel activity to the right in parallel. After run-down of the KATP channel, KR-30816 did not after the channel opening either in the absence or in the presence of UDP.

These results suggest that KR-30816 antagonizes the inhibitory effect of ATP on the K_ATPchannel in a competitive manner, thereby enhancing the channel openings.