Physiological roles of junctional membrane complex formed by Ca^<2+> store and plasma membranes in excitation-contraction coupling of cardiac myocytes.

在心肌细胞中，肌浆网（SR）膜起细胞内Ca^<2+>储存的作用。SR膜通过SR蛋白的亲核蛋白与细胞表面膜形成连接膜复合体。在这项研究中，我们探讨了由SR和肌层膜组成的连接膜复合物在兴奋-收缩耦合中的功能作用。因此，我们利用结膜亲蛋白敲除小鼠进行了以下实验。(1)观察到嗜jutopophilins基因敲除引起的异常收缩性，并对其进行了详细的描述。这种异常的收缩性被认为是由于连接膜复合物结构紊乱所致。(2)测定小鼠心脏动作电位。嗜酸蛋白敲除引起的收缩性异常是由于动作电位结构的改变。(3)小鼠心肌肌浆Ca^<2+>测定。细胞外Ca^<2+>向肌浆内流入是引起细胞收缩性异常的主要原因。(4)共聚焦激光显微镜观察到嗜酸蛋白敲除引起的肌细胞异常收缩过程中，Ca^<2+>波在肌细胞周围移动。(5) l型Ca^<2+>通道与ryanodine受体结构偶联。从全细胞电流数据计算，l型Ca^<2+>通道与ryanodine受体的偶联率因敲除亲核蛋白而降低。(6)在动物水平上研究了许多心血管系统参数。嗜酸蛋白的敲除改变了心电图的波形。心脏SR膜不仅表达嗜酸蛋白，还表达良胺受体。ryanodine受体作为Ca^<2+>-诱导Ca^<2+>释放通道，从Ca^<2+>储存在SR膜中，触发心肌收缩。因此，我们也利用ryanodine受体敲除小鼠进行了上述实验。该ryanodine受体敲除小鼠表现出异常的收缩性，这与结亲蛋白敲除小鼠不同。综上所述，目前的数据强烈表明，连接膜复合体含有亲结蛋白和良诺定受体是必不可少的兴奋-收缩耦合。结膜亲性蛋白和良诺定受体在SR膜上的完整表达对于心脏的正常收缩是重要的。少

In heart muscle cells, sarcoplasmic reticulum (SR) membranes function as the intracellular Ca^<2+> store. The SR membranes form a junctional membrane complex with cell surface membrane by juctophilins of SR proteins. In this study, we explored the functional roles of junctional membrane complex composed of SR and sarcolemmal membranes in the excitation-contraction coupling.Utilizing the junctophilin knockout mice, we thus conducted the following experiments. (1)An abnormal contractility induced by the knockout of juctophilins was obserbed and characterized in detail. The abnormal contractility was considered to be due to disorganized structures of junctional membrane complex. (2)The action potentials were measured from the mouse heart. The abnormal contractility by the knockout of juctophilins was ascribed to the alteration in the action potential configuration. (3)Myoplasmic Ca^<2+> was measured from the mouse heart. The abnormal contractility by the knockout of juctophilins was media … More ted by the influx of the extracellular Ca^<2+> into the myoplasm. (4)During the abnormal contraction by the knockout of juctophilins, Ca^<2+> waves moving around the myocytes were detected with the confocal laser microscopy. (5)L-type Ca^<2+> channel and ryanodine receptor are strucurally coupled with each other. The coupling ratio of the L-type Ca^<2+> channel and the ryanodine receptor, calculated from the whole-cell current data, was decreased by the knockout of juctophilins. (6)Many parameters of cardiovascular system were studied at the animal level. Wave forms of the electrocardiogram (ECG) were altered by the knockout of juctophilins.The cardiac SR membranes express not only juctophilins but also ryanodine receptors. The ryanodine receptors function as Ca^<2+>-induced Ca^<2+> release channels from the Ca^<2+> store in the SR membranes to trigger the heart muscle contraction. Therefore, we also conducted experiments mentioned above using the ryanodine receptor knockout mice. This ryanodine receptor knockout mice showed an abnormal contractility, which was, different from that of the junctophilin knockout animal.Taken together, the present data strongly suggest that the junctional membrane complex containing junctophilins and ryanodine receptors is essential to the excitation-contraction coupling. Intact expression of both junctophilins and ryanodine receptors in the SR membrane would be important for the normal heart contraction. Less