Ruan Ye Chun, Wang Zhe, Du Jian Yang, Zuo Wu Lin, Guo Jing Hui, Zhang Jie, Wu Zhong Luan, Wong Hau Yin, Chung Yiu Wa, Chan Hsiao Chang, Zhou Wen Liang
School of Life Science, Sun Yat-sen University, Guangzhou 510275, China.
J Physiol. 2008 Oct 15;586(20):4843-57. doi: 10.1113/jphysiol.2008.154096. Epub 2008 Aug 28.
Recent studies suggest that the epithelium might modulate the contractility of smooth muscle. However, the mechanisms underlying this regulation are unknown. The present study investigated the regulation of smooth muscle contraction by the epithelium in rat vas deferens and the possible factor(s) involved. Exogenously applied ATP inhibited electrical field stimulation (EFS)-evoked smooth muscle contraction in an epithelium-dependent manner. As the effects of ATP on smooth muscle contractility were abrogated by inhibitors of prostaglandin synthesis, but not by those of nitric oxide synthesis, prostaglandins might mediate the effects of ATP. Consistent with this idea, PGE(2) inhibited EFS-evoked smooth muscle contraction independent of the epithelium, while ATP and UTP induced the release of PGE(2) from cultured rat vas deferens epithelial cells, but not smooth muscle cells. The ATP-induced PGE(2) release from vas deferens epithelial cells was abolished by U73122, an inhibitor of phospholipase C (PLC) and BAPTA AM, a Ca(2+) chelator. ATP also transiently increased Ca(2+) in vas deferens epithelial cells. This effect of ATP on Ca(2+) was independent of extracellular Ca(2+), but abolished by the P2 receptor antagonist RB2 and U73122. In membrane potential measurements using a voltage-sensitive dye, PGE(2), but not ATP, hyperpolarized vas deferens smooth muscle cells and this effect of PGE(2) was blocked by MDL12330A, an adenylate cyclase inhibitor, and the chromanol 293B, a blocker of cAMP-dependent K(+) channels. Taken together, our results suggest that ATP inhibition of vas deferens smooth muscle contraction is epithelium dependent. The data also suggest that ATP activates P2Y receptor-coupled Ca(2+) mobilization leading to the release of PGE(2) from epithelial cells, which in turn activates cAMP-dependent K(+) channels in smooth muscle cells leading to the hyperpolarization of membrane voltage and the inhibition of vas deferens contraction. Thus, the present findings suggest a novel regulatory mechanism by which the epithelium regulates the contractility of smooth muscle.
近期研究表明，上皮细胞可能调节平滑肌的收缩性。然而，这种调节作用背后的机制尚不清楚。本研究调查了大鼠输精管中上皮细胞对平滑肌收缩的调节作用以及可能涉及的因素。外源性应用的ATP以依赖上皮细胞的方式抑制电场刺激（EFS）诱发的平滑肌收缩。由于ATP对平滑肌收缩性的影响被前列腺素合成抑制剂消除，但未被一氧化氮合成抑制剂消除，因此前列腺素可能介导了ATP的作用。与此观点一致的是，前列腺素E2（PGE2）独立于上皮细胞抑制EFS诱发的平滑肌收缩，而ATP和尿苷三磷酸（UTP）诱导培养的大鼠输精管上皮细胞释放PGE2，但不诱导平滑肌细胞释放。输精管上皮细胞中ATP诱导的PGE2释放被磷脂酶C（PLC）抑制剂U73122和钙螯合剂1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸四乙酰甲酯（BAPTA AM）消除。ATP还使输精管上皮细胞内的钙离子浓度（[Ca2+]i）短暂升高。ATP对[Ca2+]i的这种作用不依赖细胞外钙离子，但被P2受体拮抗剂RB2和U73122消除。在使用电压敏感染料进行的膜电位测量中，PGE2而非ATP使输精管平滑肌细胞超极化，并且PGE2的这种作用被腺苷酸环化酶抑制剂MDL12330A和环磷酸腺苷（cAMP）依赖性钾通道阻滞剂色满醇293B阻断。综上所述，我们的结果表明ATP对输精管平滑肌收缩的抑制作用依赖上皮细胞。数据还表明，ATP激活与P2Y受体偶联的钙离子动员，导致上皮细胞释放PGE2，进而激活平滑肌细胞中的cAMP依赖性钾通道，导致膜电压超极化并抑制输精管收缩。因此，本研究结果提示了一种上皮细胞调节平滑肌收缩性的新机制。
