Role of ryanodine receptors in the assembly of calcium release units in skeletal muscle.
Role of ryanodine receptors in the assembly of calcium release units in skeletal muscle.
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DOI：
10.1083/jcb.140.4.831
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发表时间：
1998-02-23
期刊：
影响因子：
--
通讯作者：
Allen PD
中科院分区：
文献类型：
--
作者：
Protasi F;Franzini-Armstrong C;Allen PD
抽象。在肌肉细胞中，兴奋-收缩（e-c）偶联由“钙释放单位”介导，即肌浆网（SR）和外膜之间的连接。已知在这些结构中相互面对的两种蛋白质在功能上相互作用：ryanodine受体（RyR），或SR钙释放通道，和二氢吡啶受体（DHPR），或外膜的L型钙通道。在骨骼肌中，DHPR形成四分体，即四个受体的组，并且四分体被组织成面对足阵列（或RyR）的阵列。Triadin是位于SR-外膜连接处的SR蛋白，其作用尚不清楚。我们在结构上表征了缺乏Ry 1 R的骨骼肌细胞系（1B 5）中的钙释放单位。免疫组化和冷冻断裂电镜观察发现，DHPR和triadin在分化的1B 5细胞中聚集成灶。薄切片电子显微镜显示许多SR外膜交界处缺乏足结构（dyspedic）。这些结果表明，Ry 1 Rs以外的组分负责将DHPR和三聚体靶向接合区。然而，在1B 5细胞中的DHPR不分组为四分体，在正常的骨骼肌细胞中，这表明锚定Ry 1 Rs是必要的定位DHPR成有序阵列的四分体。这一假设得到证实，发现一个“恢复四分体”的表面膜的连接域转染后的1B 5细胞与编码Ry 1 R的cDNA。
Abstract. In muscle cells, excitation–contraction (e–c) coupling is mediated by “calcium release units,” junctions between the sarcoplasmic reticulum (SR) and exterior membranes. Two proteins, which face each other, are known to functionally interact in those structures: the ryanodine receptors (RyRs), or SR calcium release channels, and the dihydropyridine receptors (DHPRs), or L-type calcium channels of exterior membranes. In skeletal muscle, DHPRs form tetrads, groups of four receptors, and tetrads are organized in arrays that face arrays of feet (or RyRs). Triadin is a protein of the SR located at the SR–exterior membrane junctions, whose role is not known. We have structurally characterized calcium release units in a skeletal muscle cell line (1B5) lacking Ry1R. Using immunohistochemistry and freeze-fracture electron microscopy, we find that DHPR and triadin are clustered in foci in differentiating 1B5 cells. Thin section electron microscopy reveals numerous SR–exterior membrane junctions lacking foot structures (dyspedic). These results suggest that components other than Ry1Rs are responsible for targeting DHPRs and triadin to junctional regions. However, DHPRs in 1B5 cells are not grouped into tetrads as in normal skeletal muscle cells suggesting that anchoring to Ry1Rs is necessary for positioning DHPRs into ordered arrays of tetrads. This hypothesis is confirmed by finding a “restoration of tetrads” in junctional domains of surface membranes after transfection of 1B5 cells with cDNA encoding for Ry1R.
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