Molecular pharmacologycal investigations on K channel openers-New

采用微电极、电压钳和膜片钳等方法，研究了新合成的K通道打开剂、尼可地尔、克罗卡林和pinacidil对家兔和大鼠门静脉、肠膜动脉和静脉平滑肌细胞的影响。兔肠系膜动脉平滑肌细胞膜电位为-7OmV，门静脉平滑肌细胞膜电位为-55mV。以上三种药物持续地使膜超极化并增加膜的离子电导。对比各药剂作用前后的电流-电压关系，各药剂均增加了膜电阻，且在-8OmV左右时，两者的关系曲线交叉。这意味着尼可地尔、pinacidil和cromakalim诱导的超极化是由于膜的K通透性增加。采用电压箝位法，在-40mV的保持电位下施加尼可地尔、克罗卡林或pinacidil时，产生的向外电流呈浓度依赖性。四乙基铵（TEA）能轻微抑制这种向外电流，4-氨基吡啶（4-AP）能显著抑制这种向外电流。这些电位变化对细胞内（胞硅）Ca非常敏感。当施加矩形去极化脉冲或斜坡电流（- 120v - +140mV）时，K电流持续增大。这三种药物引起的向外电流被格列本脲预涂阻断。当膜片钳法应用于碎片膜（内外膜片）时，记录到细胞质中Ca敏感的K通道，即Ca依赖的K电流的大电导（280pS）和小电导（30pS）。前者对TEA的敏感性高于4-AP，后者对4-AP的敏感性高于TEA。ATP（超过1mM）抑制3OpS K通道的生成，并以10mm的ATP阻断该通道。Nicorandil、pinacidil和cromakalim加速了30pS钾通道的生成，而这些Ca通道打开剂的作用被预先应用格列本脲阻断。这些K通道打开器增加了atp敏感Ca依赖的K通道的打开概率并延长了打开时间。因此，我们得出结论，K通道打开剂作用于30pS Ca依赖性ATP敏感的K通道。尼可地尔具有硝化甘油样作用，pinacidil具有二氢吡啶敏感的Ca拮抗作用，pinacidil具有肌醇1,4,5-三磷酸合成抑制剂的性质。这种作用与K通道开放可能值得作为抗心绞痛和抗高血压药。少

Effects of newly synthesized K channel openers, nicorandil, cromakalim and pinacidil on smooth muscle cells of the rabbit and rat portal vein, mesenteric artery and vein were investigated using the microelectrode, voltage clamp and patch clamp methods. The membrane potential of smooth muscle cells of the rabbit mesenteric artery was -7OmV and that of the portal vein was -55mV. Above three agents consistently hyperpolarized the membrane and increased the ionic conductance of the membrane. When the current-voltage relation-ships were compared before and after application of these agents, all agents increased the membrane resistance and both relation curves cross at about -8OmV. This means that the hyperpolarization induced by nicorandil, pinacidil and cromakalim was due to increase in the K permeability of the membrane. Using the voltage clamp method, when nicorandil, cromakalim or pinacidil was applied at the holding potantial of -40mV, the outward current generated in a concentration d … More ependent manner. This outward current was slightly inhibited by application of tetraethyl-ammonium (TEA) and markedly inhibited by 4-aminopyridine (4-AP). These potential changes were very sensitive to intracellular (cytosilic) Ca. When rectangular depolarization pulse or ramp current (-120V - +140mV) was applied, the K current was consistently enlarged. These outward current evoked by these three agents were blocked by preapplication of glibencalmide. When the patch clamp method was applied on fragmented membranes (inside out patch), the cytosolic Ca sensitive K channels were recorded, i.e. large conductance (280pS) and small conductance (30pS) of the Ca dependent K current. The former was more sensitive to TEA that 4-AP and the latter was more sensitive to 4-AP than TEA. ATP (over 1mM) inhibited the generation of the 3OpS K channel and blocked this channel with of 1OmM ATP. Nicorandil, pinacidil and cromakalim accelerated the generation of the 30pS K channel and these actions of Ca channel openers were blocked by pre- application of glibenclamide. These K channel openers the open probability and prolonged the open time of the ATP-sensitive Ca dependent K channel. Therefore, we concluded that K channel openers acts on the 30pS Ca dependent ATP sensitive K channel. Nicorandil possessed aproperty of nitroglycerine-like action, pinacidil a property of dihydropyridine sensitive Ca antagonistic action and pinacidil a property of synthesis inhibitor of inositol 1,4,5-trisphosphate. Such actions with the K channel opening may merit as anti-anginal and anti-hypertensive agents. Less