盐酸埃他卡林对心肌ATP-敏感性钾通道的作用

Effects of iptakalim hydrochloride on myocardial ATP-sensitive potassium channels

目的 在急性分离的豚鼠心室肌细胞上观察盐酸埃他卡林 (iptakalimhydrochloride ,Ipt)对钾电流的影响 ;研究Ipt对 [3 H]格列本脲 (glibenclamide ,Gli)与心肌ATP敏感性钾通道 (ATP sensitivepotassiumchannel,KATP)的硫脲受体(Sulfonylureareceptor,SUR2A)结合特征以及 [3 H]Gli与心肌膜KATP结合和解离动力学过程的影响 ,以评价Ipt对心肌KATP的作用。方法 分离豚鼠心室肌细胞 ,用全细胞记录技术记录细胞钾电流 ,通过浴槽内灌流给药 ,观察盐酸埃他卡林对钾电流的影响。KATP拮抗剂 [3 H]Gli与大鼠心肌膜特异性结合与解离的动力学试验。结果 ①Ipt在浓度为 1和10 0 μmol·L-1时 ,均可明显引起豚鼠心室肌外向钾电流I U曲线上移 ,Ipt作用后 5min内细胞外向钾电流强度分别增强为初始电流强度的 12 4 9%± 9 5 % (n =5 )和 15 1 6 %±11 2 % (n =7) ,与溶媒对照组 (6 9 8%± 3 5 % ,n =7)比较差异均有统计学意义 (P <0 0 1)。在相同条件下 ,KATP开放剂吡那地尔 (pinacidil,Pin)的作用与之相似 ,也可明显引起豚鼠心室肌外向钾电流I U曲线上移 ,显著增强细胞外向钾电流。②非标记Gli与 [3 H]Gli和大鼠心肌膜标本在 2 5℃孵育 6 0min ,可浓度依赖性地抑制 [3 H]Gli与心肌膜SUR2A的特异性结合 ,其IC50 值为 (

AIM To investigate the effects of iptakalim hydrochloride(Ipt) on potassium currents in cardiomyocytes derived from guinea pig and on the specific binding of glibenclamide (Gli) with sulfonylurea receptor(SUR_ 2A ) of ATP-sensitive potassium channel (K_ ATP ) in cardiac membranes derived from Wistar rats. The effects of Ipt on the association and dissociation kinetic processes of Gli binding with SUR_ 2A of K_ ATP in cardiac preparations were also determined. METHODS The effects of Ipt on potassium currents in cardiomyocytes were observed by using patch clamp technique(whole cell recording) after application of the drug in the bath. The experiments of the ass ociation and dissociation kinetic processes of K_ ATP blocker [ 3H]Gli binding with cardiac membranes were used. RESULTS (1)The potassium current-voltage curves (I-U curves) of cardiomyocytes derived from guinea pig were upward shifted by Ipt at the concentrations of 1 and 100 μmol·L -1 . Within 5 minutes after application of the drug, the current amplitude increased to 124.9%±9.5%(n=5)and 151.6%±11.2%(n=7)of initial current amplitude respectively(P<0.01 vs control). Under the same experimental condi-tions, the effects of pinacidil(Pin), an opener of[FQ(19*4。46,X-WZ]-K_ ATP , were similar with those of Ipt. The I-U curves of cardiomyocytes were also upward shifted by Pin at the concentrations of 1 and 100 μmol·L -1 . It increased the outward potassium currents significantly. (2)After the cardiac membrane preparations derived from rats were preincubated with unlabeled Gli and Gli for 60 minutes under 25℃, the specific binding of Gli with SUR_ 2A was inhibited by Gli in a concentration dependent manner. The IC_ 50 value was (195±62) nmol·L -1 . Under the same experimental conditions, the specific bindings of Gli with SUR_ 2A could not be displaced by Ipt at the concentrations of 1 nmol·L -1 ～1 mmol·L -1 . It also could not be displaced by Pin at the concentrations of 10 μmol·L -1 ～1 mmol·L -1 . (3) Ipt 0.1 mmol·L -1 had no effects on the association kinetic process of Gli binding with SUR_ 2A in cardiac membranes, but could accelerate the dissociation kinetic process of Gli binding with SUR_ 2A . Under the same experimental conditions, the effects of Pin were similar to those of Ipt. CONCLUSION Ipt could increase the out-ward potassium currents in myocytes. The binding sites of K_ ATP openers in SUR_ 2A were different from those of K_ ATP blockers in SUR_ 2A . The binding site of Ipt was also different from that of Gli. Ipt had allosterical modulation on the binding sites of K_ ATP blockers. Ipt could decrease the affinity of SUR_ 2A with K_ ATP blocker Gli.-