IONIC MECHANISMS OF REPOLARIZATION IN VENTRICULAR MYOCYTES

在哺乳动物中，已经描述了几种外向K+和Cl-电流 在心脏动作电位复极中起重要作用。 然而，有相当大的物种、组织和地区差异 在单个组织内(例如，室外膜和心内膜) 这些洋流的具体类型和大小。因此，在研究 从非人类哺乳动物分离的肌细胞已经阐明了生物物理 特定离子通道的性质和生理作用，它们不 有必要提供相关的人心肌细胞模型。项目 1是对负责的电流的描述 正常人脑室动作电位的复极。这个 项目分为四个项目：1)表征 复极化K+(暂态外向、延迟整流、内向整流) 和氯电流，2)抗心律失常药物的作用机制，3) Na-Ca交换电流的特性，以及4)表达克隆 一种延迟整流钾通道(L/Kr)在非洲爪哇卵母细胞上的应用。大部分 这些电流，包括K+，Cl-和Na-Ca交换电流将 使用标准的全电池电压钳技术进行研究 从心外膜和心内膜活检获得的分离细胞。 非病变组织复极电流的特征 表示用于与电池电流进行比较的基本基线数据 从患病的人体组织中分离出来的。为此，我们建议记录 从心内膜心肌活检标本分离的心肌细胞中的相同电流 对QT间期延长综合征患者进行检查，试图确定离子 这种遗传病的基础(项目2)。 几种抗心律失常药物通过延长动作电位时程发挥作用 从而延长不应期。这个 三种代表性药物多非利特和多非利特的作用机制 替地沙米(III类)和奎尼丁(1a类)]对复极电流的影响 将在分离的人心室细胞中进行研究。此外，我们 将确定早期后除极的诱导机制 这些药物，并决定了率依赖的细胞机制 多非利特延长动作电位。

In mammals, several outward K+ and Cl- currents have been described that play important roles in repolarization of cardiac action potentials. However, there are considerable species, tissue, and regional differences within a single tissue (e.g., epi- vs endocardium of ventricle) in the specific types and magnitudes of these currents. Thus, while studies of myocytes isolated from non-human mammals have elucidated the biophysical properties and physiological roles for specific ion channels, they do not necessarily provide relevant models of human cardiac myocytes. Project 1 is a characterization of the currents that are responsible for repolarization of action potentials in normal human ventricles. The project is divided into four projects: 1) characterization of repolarizing K+ (transient outward, delayed rectifier, inward rectifier) and Cl- currents, 2) mechanisms of action of antiarrhythmic drugs, 3) characterization of Na-Ca exchange current, and 4) expression cloning of a delayed rectifier K+ channel ((l/Kr) using Xenopus oocytes. Most of these currents, including K+, Cl- and Na-Ca exchange currents will be studied using standard whole cell voltage clamp techniques with freshly dissociated cells obtained from epicardial and endocardial biopsies. Characterization of repolarizing currents from nondiseased tissue represents essential baseline data for comparison to currents with cells isolated from diseased human tissue. To that end we propose to record the same currents in myocytes isolated from endomyocardial biopsy samples of patients with long QT syndrome, in an attempt to determine the ionic basis of this genetic disease (Project 2). Several antiarrhythmic drugs act by prolonging action potential duration of myocardial cells and thereby lengthen refractory period. The mechanism of action of three representative drugs [dofetilide and tedisamil (class III), and quinidine (class 1a)] on repolarizing currents will be studied in isolated human ventricular cells. Additionally, we will define the mechanisms of induction of early afterdepolarizations by these agents, and determine the cellular mechanism of rate-dependent prolongation of action potentials by dofetilide.