Mouse Models for Ion Homeostasis Defects in Heart

我们的目的是了解NHE1 Na/H交换剂和AE1、AE2、AE3和PAT1 (Slc4a1-3和Slc26a6) Cl/HCO3交换剂影响心脏Ca处理、收缩性和代谢的机制。这些酸碱转运体组成了一个控制细胞内pH （pHi）的强大系统，但这不太可能是它们的唯一功能。Na/H交换与Cl/HCO3交换耦合或单独操作的bumetanidsensitive NKCC1 Na- k - 2cl共转运体介导ph中性Na负载，进而影响Ca处理和收缩性。通过基因敲除小鼠模型，我们已经确定了几种转运蛋白对钙处理、收缩性、代谢和心脏病易感性的影响，并有证据表明ae3介导的Cl/HCO3交换和Na-K-2Cl共转运可以部分补偿其他活性的丧失。在Aim 1中，我们将使用AE1和AE2的心脏特异性敲除，以确定Cl/HCO3交换功能障碍对体内心脏功能的影响，这两种基因都可能与NHE1具有功能相互作用。在Aim 2中，分离的肌细胞和生化分析将用于确定Cl/HCO3交换器和NHE1功能障碍影响心脏钙处理、收缩性和代谢的机制。这些实验将验证以下假设，即通过这些转运体调节肌上皮下离子浓度调节钙处理和收缩性，以及NHE1和PAT1在心脏代谢和胰岛素敏感性中发挥主要调节作用。在Aim 3中，我们将验证特定的Cl/HCO3交换活动有助于肥厚的假设，以及这些活动和利尿剂敏感的NKCC1 Na-K-2Cl共转运体的活动也会影响遗传性心肌病模型中的心脏表现和心力衰竭。这些研究将为心脏中这组鲜为人知的转运蛋白的生理功能提供新的信息，并对离子转运和信号机制产生重要的见解，通过这些转运蛋白影响钙处理、收缩性和代谢。此外，这些研究将确定具有心脏保护作用的运输活动，因此不应被抑制，以及可能被抑制以引起心脏保护作用的运输活动。其中一些信息具有重要的临床意义，特别是关于代谢异常，包括胰岛素抵抗，心脏病和循环利尿剂的不良影响。

Our objective is to understand the mechanisms by which the NHE1 Na/H exchanger and the AE1, AE2, AE3, and PAT1 (Slc4a1-3 and Slc26a6) Cl/HCO3 exchangers affect cardiac Ca handling, contractility, and metabolism. These acid-base transporters comprise a robust system for control of intracellular pH (pHi), but it is unlikely that this is their only function. Na/H exchange coupled with Cl/HCO3 exchange or the bumetanidesensitive NKCC1 Na-K-2Cl cotransporter operating alone mediate pHi-neutral Na-loading, which in turn can affect Ca handling and contractility. Using gene knockout mouse models, we have identified effects on Ca handling, contractility, metabolism, and susceptibility to heart disease for several of these transporters, and have evidence that AE3-mediated Cl/HCO3 exchange and Na-K-2Cl cotransport can partially compensate for loss of the other activity. In Aim 1 we will use cardiac-specific knockouts for AE1 and AE2, both of which are likely to have functional interactions with NHE1, to determine the effects of Cl/HCO3 exchange dysfunction on cardiac performance in vivo. In Aim 2, isolated myocytes and biochemical analyses will be used to determine the mechanisms by which Cl/HCO3 exchangers and NHE1 dysfunction affects Ca handling, contractility, and metabolism in heart. These experiments will test the hypotheses that modulation of sub-sarcolemmal ion concentrations by these transporters regulates both Ca handling and contractility and that NHE1 and PAT1 exert a major regulatory effect on metabolism and insulin sensitivity in heart. In Aim 3 we will test the hypotheses that specific Cl/HCO3 exchange activities contribute to hypertrophy, and that these activities and that of the loop diuretic-sensitive NKCC1 Na-K-2Cl cotransporter also affect cardiac performance and heart failure in genetic cardiomyopathy models. These studies will provide novel information about the physiological functions of this group of poorly understood transporters in heart and yield important insights about the ion transport and signaling mechanisms by which they affect Ca handling, contractility, and metabolism. In addition, these studies will identify transport activities that are cardio-protective, and therefore should not be inhibited, and transport activities that may be inhibited to elicit cardio-protection. Some of this information has important clinical implications, particularly with regard to metabolic abnormalities, including insulin resistance, in heart disease and adverse effects of loop diuretics.