Comparative ultrastructure of Ca2+ release units in skeletal and cardiac muscle
Comparative ultrastructure of Ca2+ release units in skeletal and cardiac muscle
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DOI：
10.1111/j.1749-6632.1998.tb08253.x
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发表时间：
1998-01-01
期刊：
影响因子：
--
通讯作者：
Ramesh, V
中科院分区：
文献类型：
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作者：
Franzini-Armstrong, C;Protasi, F;Ramesh, V
横纹肌纤维的肌浆网（SR）与外膜（表面膜和横小管）相互作用以形成在兴奋-收缩偶联期间参与钙的内部释放的连接。钙通过SR的Ryanodine受体（RyR）或钙释放通道的释放受外膜的L型钙通道或二氢吡啶受体（DHPR）的控制。两种蛋白质的相互作用簇构成钙释放单元。RyR的胞质结构域可见为大的电子致密结构（足），在将SR与外膜分离的连接间隙中具有四个相同的亚基。在骨骼肌的冷冻断裂复制品中，大的膜内颗粒被分组为外膜中的四分体簇，并且四分体位于足的四个亚基的对应处。DHPR无效突变的发育不良肌纤维中四分体的缺失和DHPR cDNA转染后四分体的出现表明四分体与四种DHPR的同一性。在心肌中，DHPR位于SR-表面连接的位点，但它们不分组为四分体。这与骨骼肌中可能的直接DHPR-RyR相互作用而不是心肌中的直接DHPR-RyR相互作用一致。骨骼肌和心肌中SR表面连接的大小和分布为其功能提供了进一步的线索。
The sarcoplasmic reticulum (SR) of striated muscle fibers interacts with exterior membranes (surface membrane and transverse tubules) to form junctions that are involved in the internal release of calcium during excitation-contraction coupling. Release of calcium through the ryanodine receptors (RyRs) or calcium release channels of the SR is under the control of the L type calcium channels or dihydropyridine receptors (DHPRs) of exterior membranes. Interacting clusters of the two proteins constitute calcium release units, The cytoplasmic domains of RyRs are visible as large electron-dense structures (the feet) with four identical subunits in the junctional gap separating SR from exterior membranes. In freeze-fracture replicas of skeletal muscle, large intramembrane particles are grouped into clusters of tetrads in the exterior membranes, and the tetrads are located in correspondence of the four subunits of the feet. Lack of tetrads in dysgenic muscle fibers with a null mutation for DHPRs and appearance of the tetrads after transfection with cDNA for DHPR indicate identity of tetrads with four DHPRs, In cardiac muscle, DHPRs are located at the sites of SR-surface junctions, but they are not grouped into tetrads, This is consistent with a possible direct DHPR-RyR interaction in skeletal but not in cardiac muscle. The size and distribution of SR-surface junctions in skeletal and cardiac muscles provide further clues to their function.