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

由于K_<ATP>通道开放剂抑制气道平滑肌收缩，它们已被研究用于支气管哮喘的治疗。然而，它们的效力不同，所涉及的机制也不完全清楚。由于磷脂酰肌醇（PI）反应与气道平滑肌收缩有直接关系，我们研究了新型K_<ATP>通道打开剂Y26763对大鼠气管PI和收缩反应的影响。这些研究是在动物保护委员会批准的指导方针下进行的。用50 mg/kg戊巴比妥腹腔麻醉36只体重250 ~ 350 g的雄性Wistar大鼠，分离气管。将气管切成3mm宽的环状段进行收缩，或用Mcllwain组织切割机切成1mm宽的切片进行PI反应。首先将气管环悬挂在不锈钢挂钩之间，静息张力调整为1.5 g。用0.55 μ m的CCh诱导小鼠主动收缩，30 min后逐步添加cromakalim或Y26763诱导小鼠环松弛。其次，用[^3H]肌醇和不同浓度的cromakalim或Y26763孵育气管切片，15 min后用0.55 muM CCh孵育60 min。用柱层析法从[^3H]肌醇中分离出[^3H]肌醇单磷酸（IP_1），并用液体闪烁计数器计数。采用方差分析确定差异有统计学意义（P <0.05）。cch诱导的张力被cromakalim或Y26763剂量依赖性地减弱，Y26763的效力显著高于Y26763。1mum或更大剂量的cromakalim可增强cch诱导的IP_1积累，而Y26763则无此作用。结果表明，Y26763对气道平滑肌松弛的作用强于cromakalim，并提示这种差异可能部分归因于对PI反应的不同影响。

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.