Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
J Gen Physiol. 2010 Mar;135(3):247-59. doi: 10.1085/jgp.200910365.
Nitric oxide (NO) induces airway smooth muscle cell (SMC) relaxation, but the underlying mechanism is not well understood. Consequently, we investigated the effects of NO on airway SMC contraction, Ca(2+) signaling, and Ca(2+) sensitivity in mouse lung slices with phase-contrast and confocal microscopy. Airways that were contracted in response to the agonist 5-hydroxytryptamine (5-HT) transiently relaxed in response to the NO donor, NOC-5. This NO-induced relaxation was enhanced by zaprinast or vardenafil, two selective inhibitors of cGMP-specific phosphodiesterase-5, but blocked by ODQ, an inhibitor of soluble guanylyl cyclase, and by Rp-8-pCPT-cGMPS, an inhibitor of protein kinase G (PKG). Simultaneous measurements of airway caliber and SMC Ca(2+) revealed that airway contraction induced by 5-HT correlated with the occurrence of Ca(2+) oscillations in the airway SMCs. Airway relaxation induced by NOC-5 was accompanied by a decrease in the frequency of these Ca(2+) oscillations. The cGMP analogues and selective PKG activators 8Br-cGMP and 8pCPT-cGMP also induced airway relaxation and decreased the frequency of the Ca(2+) oscillations. NOC-5 inhibited the increase of Ca(2+) and contraction induced by the photolytic release of inositol 1,4,5-trisphosphate (IP(3)) in airway SMCs. The effect of NO on the Ca(2+) sensitivity of the airway SMCs was examined in lung slices permeabilized to Ca(2+) by treatment with caffeine and ryanodine. Neither NOC-5 nor 8pCPT-cGMP induced relaxation in agonist-contracted Ca(2+)-permeabilized airways. Consequently, we conclude that NO, acting via the cGMP-PKG pathway, induced airway SMC relaxation by predominately inhibiting the release of Ca(2+) via the IP(3) receptor to decrease the frequency of agonist-induced Ca(2+) oscillations.
一氧化氮（NO）可诱导气道平滑肌细胞（SMC）松弛，但其中的机制尚不清楚。因此，我们利用相差和共聚焦显微镜研究了 NO 对小鼠肺切片中气道 SMC 收缩、Ca（2+）信号和 Ca（2+）敏感性的影响。NO 供体 NOC-5 可使对激动剂 5-羟色胺（5-HT）收缩的气道短暂松弛，这种 NO 诱导的松弛作用被两种 cGMP 特异性磷酸二酯酶-5 选择性抑制剂扎普司特或伐地那非增强，但被可溶性鸟苷酸环化酶抑制剂 ODQ 和蛋白激酶 G（PKG）抑制剂 Rp-8-pCPT-cGMPS 阻断。同时测量气道口径和 SMC [Ca（2+）]i 发现，5-HT 诱导的气道收缩与气道 SMC 中 Ca（2+）振荡的发生相关。NOC-5 诱导的气道松弛伴随着这些 Ca（2+）振荡频率的降低。cGMP 类似物和选择性 PKG 激活剂 8Br-cGMP 和 8pCPT-cGMP 也诱导气道松弛并降低 Ca（2+）振荡的频率。NOC-5 抑制 IP（3）光解释放诱导的 [Ca（2+）]i 增加和气道 SMC 收缩。通过用咖啡因和肌醇 1,4,5-三磷酸（IP（3））处理使肺切片通透 Ca（2+），研究了 NO 对气道 SMCs Ca（2+）敏感性的影响。NOC-5 和 8pCPT-cGMP 均不能诱导激动剂收缩的 Ca（2+）通透气道松弛。因此，我们的结论是，NO 通过 cGMP-PKG 途径发挥作用，主要通过抑制 IP（3）受体释放 Ca（2+）来降低激动剂诱导的 Ca（2+）振荡频率，从而诱导气道 SMC 松弛。
