Nixon G F, Mignery G A, Somlyo A V
Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22908.
J Muscle Res Cell Motil. 1994 Dec;15(6):682-700. doi: 10.1007/BF00121075.
Although agonist stimulation leads to an increase in inositol 1,4,5-trisphosphate (InsP3) and decreased calcium in peripherally and centrally located sarcoplasmic reticulum in smooth muscle, the distribution of InsP3 receptors is unknown. InsP3 receptor and the calcium binding protein, calsequestrin were localized by immunolabelling in a tonic and a phasic smooth muscle. InsP3 receptor labelling was predominantly localized at the cell periphery, where most of the sarcoplasmic reticulum is localized in vas deferens (phasic muscle). Elements of central sarcoplasmic reticulum, where present, were also labelled. Distribution of calsequestrin in vas deferens was similar to that of the InsP3 receptor. In aorta (tonic muscle) the InsP3 receptor labelling was proportional to sarcoplasmic reticulum distribution: predominantly central. No labelling of sections or immunoblots was observed with the anti-calsequestrin antibody in aorta. InsP3 and caffeine, but not cyclic ADP-ribose, released intracellular Ca2+ in permeabilized vas deferens and aorta. The ultrastructure of the sarcoplasmic reticulum, investigated in stereo views of semi-thick and thin sections of osmium ferricyanide stained tissue, is shown to have several distinctive features, such as fenestrated sheets (single or in stacks), as well as numerous regions of continuity between central and peripheral sarcoplasmic reticulum, suggesting a single compartment within the smooth muscle cell. Regions of the sarcoplasmic reticulum were closely apposed to and often ensheathed mitochondria. We conclude that InsP3 receptors are present in both the central and the peripheral sarcoplasmic reticulum of tonic and phasic smooth muscle, consistent with electron probe analysis results showing calcium release from both regions.
尽管激动剂刺激会导致平滑肌外周和中央肌浆网中的肌醇1,4,5 -三磷酸（InsP3）增加以及钙减少，但InsP3受体的分布尚不清楚。通过免疫标记在一种紧张性和平滑性平滑肌中定位了InsP3受体和钙结合蛋白——肌集钙蛋白。InsP3受体标记主要定位于细胞周边，在输精管（平滑肌）中大部分肌浆网也位于此处。中央肌浆网的成分（若存在）也被标记。输精管中肌集钙蛋白的分布与InsP3受体相似。在主动脉（紧张性肌肉）中，InsP3受体标记与肌浆网分布成正比：主要位于中央。在主动脉中，抗肌集钙蛋白抗体未观察到切片或免疫印迹的标记。InsP3和咖啡因，但不是环ADP -核糖，可使通透的输精管和主动脉释放细胞内Ca2+。通过对锇铁氰化物染色组织的半厚和超薄切片的立体观察研究的肌浆网超微结构显示有几个独特特征，如多孔片层（单个或堆叠），以及中央和外周肌浆网之间的许多连续区域，提示平滑肌细胞内为单一隔室。肌浆网区域与线粒体紧密相邻且常包裹在线粒体周围。我们得出结论，InsP3受体存在于紧张性和平滑性平滑肌的中央和外周肌浆网中，这与电子探针分析结果一致，即显示钙从这两个区域释放。
