CA+2 AND NA+ TRANSPORT AND ARRHYTHMIAS IN HEART FAILURE

这些研究的目的是确定Ca和Na转运改变在心力衰竭（HF）室性心动过速（VT）发展中的作用。我们最近的研究表明，兔和人衰竭心脏的VT是由一种不可重入的机制引发的，这种机制可能是由于延迟后去极化（DADs）（或早期后去极化（EADs））引发的活动。我们还发现HF中Na/Ca交换（NaCaX） mRNA、蛋白质和电流的上调，这可能是导致DADs的瞬时内向电流（I-ti）的基础。我们假设在HF中，动作电位持续时间（APD）的延长和[Na]1的增加（由于Na/K atp酶活性的降低）有助于SR Ca过载和自发的SR Ca释放。此外，在HF中给定的SR Ca释放将产生更大的I-ti（由于NaCaX增加）和更大的DADs（由于I-ti增加和1-K1减少），导致更多的触发APs和HF中不可重入性心律失常。具体目标将集中在：1 .改变APD和离子电流对HF中SR Ca负载和DAD诱导的作用。2. HF患者胞内[Na]和Na/ k - atp酶活性及表达的变化。3. SR - Ca释放与致心律失常I- ti's、dad及触发ap发生的关系。4. HF患者自发性SR Ca释放对EADs的可能贡献。5. 通过NaCaX（与KB-R7943一起）阻断Ca内流对E-C偶联、肌细胞中I-ti和DADs的预防以及对完整衰竭原位心脏VT的预防的影响。实验方法包括：体外膜片箝位（电压、AP和电流箝位）；[Ca]i和[Na]i的荧光测定；测定mRNA和蛋白（Ca转运体和Na/K atp酶亚基亚型）和Na/K atp酶活性；以及体内的三维心脏测绘。在一种新的非缺血性心力衰竭致心律失常兔模型中的详细研究将扩展到包括从衰竭和非衰竭人类心脏分离的心室肌细胞的研究。这些研究的结果将为开发有效的治疗方法提供基础，以调节室性心动过速的不可重入性起始，并降低心力衰竭患者猝死的高发率。

The goal of these studies is to define the role of altered Ca and Na transport in the development of ventricular tachycardia (VT) in heart failure (HF). We have recently shown that VT in the failing rabbit & human heart initiates by a nonreentrant" mechanism that may be due to triggered activity from delayed afterdepolarizations (DADs) (or early afterdepolarizations, EADs). We also find upregulation of Na/Ca exchange (NaCaX) mRNA, protein and current in HF which could underlie the transient inward current (I-ti) responsible for DADs. We hypothesize that in HF, prolongation of the action potential duration (APD) and increased [Na]1 (due to decreased Na/K ATPase activity) contribute to SR Ca overload and spontaneous SR Ca release. Further, a given SR Ca release in HF will produce greater I-ti (due to increased NaCaX) and larger DADs (due to increased I-ti and reduced 1-K1), resulting in more triggered APs and nonreentrant arrhythmias in HF. Specific Aims will focus on: l. The role of altered APD & ionic currents on both SR Ca load and DAD induction in HF. 2. The alterations in intracellular [Na] and Na/K-ATPase activity & expression in HF. 3. The relationship of SR Ca release to the genesis of arrhythmogenic I- ti's, DADs and triggered APs. 4. The possible contribution of spontaneous SR Ca release to EADs in HF. 5. The effects of blocking Ca influx via NaCaX (with KB-R7943) on E-C coupling, on prevention of I-ti and DADs in myocytes, and on prevention of VT in the intact failing heart in situ. The experimental approaches will include: in vitro patch clamping (voltage, AP & current clamp); fluorescence measurements of [Ca]i and [Na]i; measurement of mRNA & protein (of Ca transporters & Na/K ATPase subunit isoforms) and Na/K ATPase activity; and 3-dimensional cardiac mapping in vivo. Detailed studies in a novel arrhythmogenic rabbit model of nonischemic HF will be extended to include studies in isolated ventricular myocytes from failing and nonfailing human hearts. The results of these studies will provide the foundation for the development of effective therapeutic approaches to modulate nonreentrant initiation of VT and to decrease the high incidence of sudden death in patients with heart failure.