Mouse Models for Ion Homeostasis Defects in Heart

我们的目标是了解NHE 1 Na/H交换器和AE 1、AE 2、AE 3和PAT 1（Slc 4a 1 -3和Slc 26 a6）Cl/HCO 3交换器影响心脏Ca处理、收缩性和代谢的机制。这些酸碱转运蛋白构成了控制细胞内pH（pHi）的强大系统，但这不太可能是它们唯一的功能。Na/H交换结合Cl/HCO 3交换或单独操作的布美他尼敏感性NKCC 1 Na-K-2Cl协同转运蛋白介导pH中性Na负载，这反过来又会影响Ca处理和收缩性。使用基因敲除小鼠模型，我们已经确定了这些转运蛋白中的几种对钙处理、收缩性、代谢和心脏病易感性的影响，并且有证据表明AE 3介导的Cl/HCO 3交换和Na-K-2Cl共转运可以部分补偿其他活性的损失。在目标1中，我们将使用心脏特异性敲除AE 1和AE 2，这两者都可能与NHE 1有功能性相互作用，以确定Cl/HCO 3交换功能障碍对体内心脏性能的影响。在目标2中，分离的心肌细胞和生化分析将用于确定Cl/HCO 3交换器和NHE 1功能障碍影响心脏中的Ca处理、收缩性和代谢的机制。这些实验将测试的假设，这些转运蛋白的肌膜下离子浓度的调制调节钙处理和收缩性，NHE 1和PAT 1发挥了主要的调节作用，心脏的代谢和胰岛素敏感性。在目标3中，我们将检验以下假设：特定的Cl/HCO 3交换活动有助于肥大，并且这些活动和袢利尿剂敏感的NKCC 1 Na-K-2Cl协同转运蛋白的活动也影响遗传性心肌病模型中的心脏性能和心力衰竭。这些研究将提供新的信息，这一组知之甚少的转运蛋白在心脏的生理功能，并产生重要的见解离子转运和信号传导机制，它们影响钙处理，收缩性和代谢。此外，这些研究将确定具有心脏保护作用的转运活动，因此不应受到抑制，以及可能受到抑制以引起心脏保护的转运活动。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，心脏病和袢利尿剂的不良反应。

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.