Role of Ca-activated K channel and Na pump in the regulation of airway smmoth muscle tone.

1.肌肉收缩和松弛反应将分离的支气管段固定在器官腔内，在K通道阻滞剂和哇巴因存在或不存在的情况下，测定对乙酰胆碱的收缩反应和对各种支气管扩张剂的松弛反应。沙丁胺醇、福司可林和硝普钠对乙酰胆碱引起的收缩反应有增强作用，沙丁胺醇、福司可林和硝普钠的松弛反应可被这些药物减弱，而格列本脲和阿帕明则无作用。因此，钙激活的钾通道和钠泵通过去极化膜电位在调节气道平滑肌张力中发挥作用。环核苷酸的积累细胞内环核苷酸浓度是在存在和不存在轮藻毒素和哇巴因的情况下测定的。沙丁胺醇和福司可林使cAMP含量增加，硝普钠使cGMP含量增加，而这些作用不被胆毒素和哇巴因所改变，表明细胞内cAMP和cGMP直接兴奋气道平滑肌细胞钙激活的钾通道和钠泵。膜片钳研究DBcAMP和DBcGMP的加入分别引起单个K通道离子电流。因此，证实了这些环核苷酸具有钙激活钾通道开放和Na-K-ATPase激活作用。

1. Muscle contractile and relaxant responsesIsolated bronchial segments were mounted in organ chambers and the contractile responses to acetylcholine and the relaxant responses to various bronchodilating agents were determined in the presence and absence of K channel blockers and ouabain. Acetylcholine-induced contrction was potentiated by charybdotoxin and ouabain, and the relaxant responses to salbutamol, forskolin and nitroprusside were attenuated by these drugs, whereas glibenclamide and apamin had no effect. Thus, Ca-activated K channel and Na pump play roles in the regulation of airway smooth muscle tone by depolarizing membrane potential.2. Accumulation of cyclic nucleotidesIntracellular cyclic nucleotide concentrations were determined in the presence and absence of charybdotoxin and ouabain. Salbutamol and forskolin increased cAMP conctents and nitroprusside increased cGMP contents, and these effects were not altered by charybdotoxin and ouabain, indicating that intracellular cAMP and cGMP directly stimulate Ca-activated K channel and Na pump in airway smooth muscle cells.3. Patch clamp studiesAddition of DBcAMP and DBcGMP each caused single K channel ion current. Therefore, it was confirmed that these cyclic nucleotides produce Ca-activated K channel opening and Na-K-ATPase activation.