Tsunobuchi-Ushijima H, Ikoma K, Gomi Y
Department of Pharmacology, Faculty of Pharmaceutical Science, Kanazawa University, Japan.
Jpn J Pharmacol. 1998 Nov;78(3):323-9. doi: 10.1254/jjp.78.323.
The cellular mechanisms of norepinephrine (NE)-induced Mn2+-dependent contractions were investigated in dispersed smooth muscle cells from guinea pig vas deferens by characterizing the effects of NE and K+ on cell length observed by videotape microscopy and on intracellular Mn2+ and Ca2+ concentration ([Mn2+]i and [Ca2+]i) observed by confocal microscopy. Both stimulants induced slow sustained contraction in Ca2+-depleted, Mn2+-accumulated cells (Mn2+-loaded cells), whereas they induced biphasic contractions in normal cells that were neither Ca2+-depleted nor Mn2+-loaded. In both conditions, the number of cells responding to NE as well as the magnitude of NE-induced contractions increased in a dose-dependent manner. Contractions induced by K+ in Mn2+-loaded strip preparations were markedly smaller than those induced by NE. Although individual K+-induced contractions in responsive Mn2+-loaded cells were as large as those induced by NE, a much smaller percentage of Mn2+-loaded cells was responsive to K+ than to NE. These results are consistent with the idea that the contractions of strip preparations may reflect the magnitude of the contractions of individual cells as well as the percentage of responsive cells in the preparations. Inconsistent with the contractions, the [Mn2+]i rise induced by K+ was larger than that induced by NE, and the percentage of cells responsive to K+ was larger than that responsive to NE. These results suggest that NE may increase the Mn2+ sensitivity of contractile elements.
通过录像显微镜观察去甲肾上腺素（NE）和钾离子（K⁺）对豚鼠输精管分散平滑肌细胞长度的影响，以及通过共聚焦显微镜观察它们对细胞内锰离子（Mn²⁺）和钙离子（Ca²⁺）浓度（[Mn²⁺]i和[Ca²⁺]i）的影响，研究了NE诱导的锰离子依赖性收缩的细胞机制。两种刺激物在钙离子耗尽、锰离子蓄积的细胞（锰离子负载细胞）中均诱导缓慢持续收缩，而在既未钙离子耗尽也未锰离子负载的正常细胞中诱导双相收缩。在这两种情况下，对NE作出反应的细胞数量以及NE诱导的收缩幅度均呈剂量依赖性增加。在锰离子负载的条带制剂中，K⁺诱导的收缩明显小于NE诱导的收缩。尽管在有反应的锰离子负载细胞中，单个K⁺诱导的收缩与NE诱导的收缩一样大，但对K⁺有反应的锰离子负载细胞的百分比远低于对NE有反应的细胞百分比。这些结果与条带制剂的收缩可能反映单个细胞收缩幅度以及制剂中有反应细胞百分比的观点一致。与收缩情况不一致的是，K⁺诱导的[Mn²⁺]i升高大于NE诱导的升高，且对K⁺有反应的细胞百分比大于对NE有反应的细胞百分比。这些结果表明，NE可能会增加收缩元件对锰离子的敏感性。
