平滑肌BKCa通道在运动改变大鼠胸主动脉舒缩特性中的作用

背景：大电导钙激活钾通道(BK_Ca)是调节细胞兴奋性和血管张力的重要离子通道，有关大动脉平滑肌BK_Ca通道的作用机制鲜有报道。目的：观察有氧运动对大鼠胸主动脉舒缩特性的影响，并探讨平滑肌BK_Ca通道在其中的作用。方法：将20只Wistar大鼠随机分为安静对照组和有氧运动组，运动组进行12周跑台运动，坡度0°, 20 m/min, 60 min/d, 5 d/周。之后每组5只大鼠行股动静脉插管术。恢复1 d后，于在体、清醒状态下进行心血管功能监测。另各组5只大鼠，取胸主动脉制备去内皮血管环，进行体外血管收缩特性检测。结果与结论：①有氧运动后静脉注射去甲肾上腺素引起的升压反应幅度下降。②静脉注射BK_Ca通道阻断剂Iberiotoxin可诱发升压反应，且运动组更显著。③ 120 mmol/L KCl在两组胸主动脉血管环均可诱发收缩，最大张力差异无显著性意义。④去甲肾上腺素(10^-9~10^-5 mol/L)诱发的血管收缩呈浓度依赖性，但运动组的最大张力显著低于安静组。⑤Iberiotoxin (3×10^-8 mol/L)预处理血管后，可增强去甲肾上腺素(10^-5 mol/L)诱发的张力增加，且运动组增加幅度显著大于安静组。⑥BKCa通道开放剂NS1619 (10^-10~10^-6 mol/L)可引起去甲肾上腺素诱发的血管收缩张力下降，且运动组对其敏感性(pD2)增加。提示，有氧运动可诱导大鼠心血管反应性和胸主动脉舒缩特性改变，其中平滑肌BKCa通道起着重要作用。

Effect of smooth muscle large-conductance Ca2+-activated K+ channel on alteration of the thoracic aortic contractility induced by exercise training

BACKGROUND:Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels play a critical role in regulating the cellular excitability and vascular tone. The reports about the mechanisms of the smooth muscle BK_Ca channels on the conduit arteries are rare.OBJECTIVE:To investigate the effects of aerobic exercise on the rat thoracic aortic contractility, and to explore the possible BK_Ca channel mechanisms underlying these effects.METHODS:Twenty male Wistar rats were randomly divided into sedentary group and aerobic exercise group. Rats in the aerobic exercise group were preformed with 12 week-treadmill exercise, 0° slope, 20 m/min, 60 min/d, 5 d/wk. After 12 weeks, some animals (n=5 in each group) underwent femoral arterial and venous cannulation. Following 1 day recovery, the cardiovascular responses were monitored in vivo without anesthesia. For the rest animals (n=5 in each group), the thoracic aorta was carefully dissected free, cut into rings, and the endothelial cell lining was removed. The vessel contractility was examined in vitro.RESULTS AND CONCOUSION:①The pressor responses induced by intravenous injection of norepinephrine were attenuated in the aerobic exercise group. ②Intravenous injection of iberiotoxin, a selective BK_Ca channel blocker, caused a pressor response, which was more prominent in aerobic exercise group. ③120 mmol/L KCl elicited a significantly increase of vascular tone in both groups, and there was no significant differences of the maximal tension between two groups. ④Norepinephrine (10^-9-10^-5 mol/L) induced a concentration-dependent contraction of thoracic aorta in both groups, while the maximal tension in exercise group was significant less than that in the sedentary group. ⑤Iberiotoxin (3×10^-8 mol/L) pretreatment could enhance the NE-induced tension increase, which was more significant in exercise training group. ⑥BKCa channel opener NS1619 (10^-10-10^-6 mol/L) could cause a decrease of norepinephrine-induced vascular contraction, and the sensitivity of tissue to NS619 (pD2) was higher in exercise group than that in the sedentary group. These results suggest that aerobic exercise can change the cardiovascular reactivity and vascular contractility, in which the smooth muscle BKCa channels play an important role.