Action Potential Shortening and Negative Inotropic Effects of a Novel Potassium Channel Opener, NIP-121, as Compared with Cromakalim in Guinea Pig Ventricular Myocardium

The potencies of NIP-121, a new potassium channel opener, to shorten action potential duration and to decrease the contractile force was examined using isolated guinea pig right ventricular free wall and papillary muscle preparations, respectively; and they were compared with those of cromakalim. NIP-121 was about 10 times more potent than cromakalim with respect to both effects. This potency ratio in cardiac muscle was about the same as that observed in rat aorta and portal vein. These cardiac effects of both agents were antagonized by glibenclamide.