Abstract: AIM: To investigate the relaxation effects of iptakalim (Ipt), a novel structural ATP-sensitive potassium channel opener (KCO), compare the relaxation characteristics of Ipt to the other structurally diverse KCOs, pinacidil (Pin)and diazoxide (Dia), and further understand the relaxation selectivity of Ipt. METHODS: Strips of stomach, ileum, and bladder isolated from rats were prepared and treated with different concentrations of drugs after contraction of 10^-5 mol·L^-1 acetylcholine. RESULTS: Ipt at the concentrations of 10^-8-10^-4 mol·L^-1 caused no relaxation effects on strips of stomach, ileum and bladder. The same results as Ipt were detected in diazoxide-treated tissue strips. Pin showed no effects on strips of stomach and bladder, however, Pin at concentrations of 10^-5 and 10-4mol·L^-1 induced significant relaxations in ileum strips compared with the former concentration, and the relaxation rates were 28.8 % and 51.9 %, respectively. CONCLUSION: Ipt shows no effect on the relaxation of stomach, ileum and bladder, which is different from Pin, but the same as Dia. Moreover, similarities and differences in relaxation are also found among the structurally diverse KCOs.

Key words: iptakalim, ATP-sensitive potassium channel, ATP-sensitive potassium channel opener, nonvascular smooth muscles pinacidil, diazoxide, hypertension, acetylcholine