Pharmacologic profiles of YM934, a novel potassium channel opener

Pharmacologic profiles of YM934, a newly synthesized 1,4-benzoxazin derivative K channel opener were evaluated in in vitro and in vivo experiments. In isolated rat portal vein, YM934 and a benzopyran derivative K channel opener lemakalim inhibited the frequency of spontaneous rhythmic contractions concentration de-pendently, with IC₅₀ values of 14 and 38 μM, respectively. These inhibitory effects were competitively antagonized by glibenclamide (an ATP-sensitive K channel blocker; 10^-7-3 x 10^-6 M). In isolated rabbit aorta, YM934 (10^-8-10^-6 M) and lemakalim (10^-8l0^-6 M) relaxed the contractions induced by 20 mAf KC1 concentration dependency but were ineffective against the contractions induced by 50 mM KC1. YM934 (10^-8-3 x KT⁶ M) and lemakalim (3 x 10^-8-10^-5 M), but not the calcium antagonist nifedipine, relaxed the contractions induced by norepinephrine (NE 10^-6 M) or prostaglandin F_2α (PGF_2α 3 x 10^-6 M) in the aorta. In pentobarbital-anesthetized dogs, YM934 (1-10 μg/kg intravenously, i.v.) dose-dependently increased coronary artery blood flow (CBF), and decreased total peripheral resistance (TPR) and mean blood pressure (MBP). YM934 selectively increased CBF, but had little effect on vertebral, carotid, mesenteric, renal and femoral artery BF. These vasodilatory effects of YM934 were antagonized by glibenclamide. YM934 is a potent K channel opener and possesses potent vasodilatory effects, with particularly pronounced effects on the coronary artery. These effects of YM934 may, like lemakalim, be mediated by opening of ATP-sensitive K channels.