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

这些研究的目的是确定钙和钠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，在衰竭的家兔和人类心脏中，室性心动过速是由一种非折返性机制引发的，这种机制可能是由于延迟后除极（DAD）（或早期后除极，埃兹）触发的。我们还发现HF中Na/Ca交换（NaCaX）mRNA、蛋白和电流的上调，这可能是导致DAD的瞬时内向电流（I-ti）的基础。我们假设在HF中，动作电位时程（APD）的延长和[Na]1增加（由于Na/K ATP酶活性降低）有助于SR Ca超载和自发SR Ca释放。此外，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DAD（由于I-ti增加和1-K1减少），导致HF中更多的触发AP和非折返性心律失常。具体目标将集中在：l。改变APD和离子电流对HF中SR Ca负荷和DAD诱导的作用。2. HF中细胞内[Na]和Na/K-ATP酶活性及表达的改变。3. SR Ca释放与致炎性I- ti's、DAD和触发性AP发生的关系。4.自发性SR Ca释放对HF中埃兹的可能贡献。5.通过NaCaX（用KB-R7943）阻断Ca内流对E-C偶联、对预防心肌细胞中的I-ti和DAD以及对预防原位完整衰竭心脏中的VT的影响。实验方法将包括：体外膜片钳（电压、AP和电流钳）;[Ca]i和[Na]i的荧光测量; mRNA和蛋白质（Ca转运蛋白和Na/K ATP酶亚基亚型）和Na/K ATP酶活性的测量;以及体内三维心脏标测。在一种新的致瘤兔非缺血性HF模型中的详细研究将扩展到包括在来自衰竭和非衰竭人类心脏的分离心室肌细胞中的研究。这些研究的结果将为开发有效的治疗方法提供基础，以调节非折返性VT的起始，并降低心力衰竭患者猝死的高发生率。

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.