CELLULAR BIOLOGY OF CARDIAC SODIUM-CALCIUM EXCHANGE

描述（由申请人提供）：心脏肌膜钠钙交换器（NCX）是从肌细胞中排出钙的主要机制。因此，交换器是细胞内Ca和心肌收缩力的重要调节剂。本申请的长期目标是进一步了解钠钙交换器在兴奋-收缩（EC）偶联中的重要性。钠钙交换器水平的遗传改变对EC偶联产生了意想不到的影响。建议的两个项目如下：1。心脏EC偶联对遗传改变的Na-Ca交换水平的适应。在PI实验室中建立了Na-Ca交换剂水平变化较大的小鼠。这些小鼠中最令人感兴趣的是转基因纯合NCX过表达（活性增加> 3倍）和心脏特异性NCX敲除（KO）小鼠。NCX KO小鼠出乎意料地活到成年，并表现出EC偶联途径的惊人可塑性。心肌通过减少80%的钙流入肌细胞来适应初级钙外排机制的缺失。实验提出了探索这种适应的各种机制的贡献。2. EC偶联增益改变的生物化学相关性。过表达的肌膜钠钙交换诱导的二氢吡啶受体（DHPR或L型钙通道）的膜环境的变化，DHPR位于野生型肌细胞的脂筏，但不再分馏在脂筏中的NCX过表达的肌细胞。与这种重新分布相关的是EC耦合增益的降低。我们假设NCX的过度表达改变了DHPR和兰尼碱受体之间的物理关系，导致这些蛋白质之间的偶联减少，从而降低了增益。了解NCX如何与EC偶联机制相互作用对于了解心力衰竭和其他病理学中改变的Ca通量至关重要。NCX对EC偶联具有意想不到的调节作用，具有药理学意义。

DESCRIPTION (provided by applicant): The cardiac sarcolemmal Na-Ca exchanger (NCX) is the primary mechanism for the extrusion of Ca from myocytes. As such, the exchanger is an important regulator of intracellular Ca and cardiac contractility. The long-term objective of this application is to further understand the significance of the Na-Ca exchanger in excitation-contraction (EC) coupling. Genetic alterations in the level of the Na-Ca exchanger have had unexpected effects on EC coupling. The two proposed projects are as follows: 1. Adaptations of cardiac EC coupling to genetically altered levels of Na-Ca exchanger. Mice with large changes in the level of the Na-Ca exchanger have been created in the laboratory of the PI. The most interesting of these mice are transgenic homozygous NCX overexpressors (>3-fold increase in activity) and cardiac-specific NCX knockout (KO) mice. The NCX KO mice unexpectedly live to adulthood and demonstrate a surprising plasticity of EC coupling pathways. The myocardium adapts to the absence of the primary Ca efflux mechanism by decreasing Ca influx into myocytes by 80%. Experiments are proposed to explore the contributions of various mechanisms to this adaptation. 2. A biochemical correlate of altered gain of EC coupling. Overexpression of the sarcolemmal Na-Ca exchanger induces a change in the membrane environment of the dihydropyridine receptor (DHPR or L-type Ca channel); the DHPR is located in lipid rafts in wild type myocytes, but the DHPR no longer fractionates in lipid rafts in NCX-overexpressing myocytes. Correlating with this re-distribution is a decrease in the gain of EC coupling. We hypothesize that overexpression of NCX changes the physical relationship between DHPRs and ryanodine receptors which leads to diminished coupling between these proteins and a decrease in gain. Understanding how NCX interacts with the EC coupling machinery is essential to understanding the altered Ca fluxes in heart failure and other pathologies. NCX has unexpected regulatory effects on EC coupling with pharmacological implications.