Calcium cycling protein density and functional importance to automaticity of isolated sinoatrial nodal cells are independent of cell size
Calcium cycling protein density and functional importance to automaticity of isolated sinoatrial nodal cells are independent of cell size
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DOI：
10.1161/circresaha.107.153676
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发表时间：
2007-06-22
影响因子：
20.1
通讯作者：
Lakatta, Edward G.
中科院分区：
文献类型：
--
作者：
Lyashkov, Alexey E.;Juhaszova, Magdalena;Lakatta, Edward G.
在心脏窦房结细胞舒张晚期去极化过程中，细胞膜下发生自发的、局部的、节律性的Ryanodine受体（RyRs）Ca 2+释放。这些激活Na+/Ca 2+交换器（NCX 1）产生内向电流和膜兴奋，驱动正常的自发搏动。然而，RyR和NCX串扰的拟议功能的形态背景尚未得到证明。在这里，我们表明，RyRs和SERCA 2的平均分离SANC全细胞标记密度与心房和心室肌细胞相似，并且在所有大小的SANC中相似。NCX 1的标记在所有大小的SANC中也是相似的，并且超过心房和心室肌细胞中的标记。NCX 1和心脏RyR（cRyR）在所有SANC中的膜下共定位超过在其他细胞类型中的共定位。此外，完整兔窦房结（SAN）的Cx43阴性初级起搏区显示出cRyR、NCX 1和SERCA 2的强阳性标记。在分离的SANC的功能研究表明，无论是平均动作电位（AP）的特性，也不是那些细胞内Ca 2+释放，也不是自发周期长度随细胞大小而变化。螯合细胞内[Ca 2 +]，或禁用RyR或NCX 1，显着减弱或消除所有SANC中的自发SANC搏动。因此，在小尺寸的SANC中存在SERCA 2、RyR和NCX 1的密集标记，这些SANC被认为驻留在SAN中心（冲动起始的位点）内。由于这些细胞的正常自律性需要完整的Ca 2+循环，因此SERCA、RyR 2和NCX分子的相互作用涉及SAN冲动的启动。
Spontaneous, localized, rhythmic ryanodine receptor (RyRs) Ca2+ releases occur beneath the cell membrane during late diastolic depolarization in cardiac sinoatrial nodal cells (SANCs). These activate the Na+/Ca2+ exchanger (NCX1) to generate inward current and membrane excitation that drives normal spontaneous beating. The morphological background for the proposed functional of RyR and NCX crosstalk, however, has not been demonstrated. Here we show that the average isolated SANC whole cell labeling density of RyRs and SERCA2 is similar to atrial and ventricle myocytes, and is similar among SANCs of all sizes. Labeling of NCX1 is also similar among SANCs of all sizes and exceeds that in atrial and ventricle myocytes. Submembrane colocalization of NCX1 and cardiac RyR (cRyR) in all SANCs exceeds that in the other cell types. Further, the Cx43 negative primary pacemaker area of the intact rabbit sinoatrial node (SAN) exhibits robust positive labeling for cRyR, NCX1, and SERCA2. Functional studies in isolated SANCs show that neither the average action potential (AP) characteristics, nor those of intracellular Ca2+ releases, nor the spontaneous cycle length vary with cell size. Chelation of intracellular [Ca2+], or disabling RyRs or NCX1, markedly attenuates or abolishes spontaneous SANC beating in all SANCs. Thus, there is dense labeling of SERCA2, RyRs, and NCX1 in small-sized SANCs, thought to reside within the SAN center, the site of impulse initiation. Because normal automaticity of these cells requires intact Ca2+ cycling, interactions of SERCA, RyR2 and NCX molecules are implicated in the initiation of the SAN impulse.