ROLES OF PHOSPHATIDYLINOSITOL IN THE MECHANISMS INVOLVED IN THE AIRWAY SMOOTH MUSCLE RELAXATION INDUCED BY ATP-SENSITIVE POTASSIUM CHANNEL OPENERS

由于钾通道<ATP>开放剂能抑制气道平滑肌收缩，因此被研究用于治疗支气管哮喘。然而，它们的效力不同，所涉及的机制尚未完全阐明。由于磷脂酰肌醇（PI）反应与气道平滑肌收缩有直接关系，本研究<ATP>在动物保护委员会批准的指导原则下，观察了新型K通道开放剂Y26763对大鼠气管PI反应和气道平滑肌收缩反应的影响。将36只体重为250-350 g的雄性Wistar大鼠用50 mg/kg的戊巴比妥腹腔内麻醉并分离气管。将气管切成3 mm宽的环段用于收缩，或用Mclllord组织切碎机切成1 mm宽的切片用于PI反应。首先，将气管环悬挂在不锈钢钩之间，并将静息张力调节至1.5g。用0.55 μ M卡巴胆碱（CCh）诱导主动收缩，30分钟后，通过逐步累积添加色满卡林或Y26763诱导环松弛。第二，将气管切片与[^3H]肌醇和不同浓度的克罗卡林或Y26763一起孵育，15分钟后将切片与0.55 μ M的CCh一起孵育60分钟。通过柱色谱法将形成的[^3H]肌醇单磷酸（IP_1）与[^3H]肌醇分离，并用液体闪烁计数器计数。使用ANOVA确定统计学显著性（P &lt;0.05）ACh诱导的张力被cromakalim或Y26763剂量依赖性地减弱，其中Y26763的效力显著更高。1 μ M或更高剂量的色满卡林（cromakalim）可增强CCh诱导的IP_1蓄积，而Y26763则无此作用。结果表明Y26763对气道平滑肌的舒张作用强于色满卡林，这可能与其对PI反应的不同作用有关。

Since K_<ATP> channel openers suppress the airway smooth muscle contraction, they have been investigated for the treatment of bronchial asthma. However, their potencies are different and the mechanisms involved are not fully clarified. Since there is a direct relationship between phosphatidylinositol (PI) response and airway smooth muscle contraction, we examined the effects of Y26763, a novel K_<ATP> channel opener, on PI and contractile responses of rat trachea.The studies were conducted under guidelines approved by the Animal Care Committee. Thirty-six Male Wistar rats weighing 250-350 g were anesthetized with 50 mg/kg intraperitoneal pentobarbital and the trachea was isolated. The trachea was chopped into 3-mm-wide ring segments for the contraction, or chopped into 1-mm-wide slices for PI response with a Mcllwain tissue chopper. First, the trachea rings were suspended between stainless hooks and the resting tension was adjusted to 1.5 g. Active contraction was induced with 0.55 muM Carbachol (CCh) and 30 min later, ring relaxation was induced by stepwise cumulative additions of cromakalim or Y26763. Second, the tracheal slices were incubated with [^3H]myo-inositol and various concentrations of cromakalim or Y26763, and 15 min later the slices were incubated with 0.55 muM CCh for 60 min. The [^3H]inositol monophosphate (IP_1) formed was separated from [^3H]myo-inositol by column chromatography and counted with a liquid scintillation counter. Statistical significance (P <0.05) was determined using ANOVA.CCh-induced tension was attenuated dose-dependently by either cromakalim or Y26763 with a significantly greater potency of Y26763. CCh-induced IP_1 accumulation was potentiated by cromakalim at a dose of 1 muM or greater, but not by Y26763.Results show that Y26763 has a stronger effect on airway smooth muscle relaxation than cromakalim, and suggest that the difference might be accounted in part by the differential effects on PI response.