CLONING AND EXPESSION OF A CARDIAC T TYPE CA CHANNEL

细胞内钙控制着多种细胞功能，例如 收缩、分泌、增殖和基因表达。 之一 钙流入心肌细胞的主要途径是通过T-和 L型电压门控Ca 2+通道。 T型或低压激活 (LVA)通道，在膜的小去极化后打开。 t型 在心房肌细胞和起搏细胞中发现了电流， 它们参与决定起搏器活动。 多种药物阻断 L型通道，然而，没有T型的选择性阻断剂 渠道 这项研究的长期目标之一是提供 一种允许T型通道发育的测定系统， 阻滞剂。 钙离子通道是一种多亚基复合物， 大离子传导亚单位α 1和几个附件 亚基（α 2 δ，β和γ）。 编码α 1的六个基因 亚单位已被克隆。 通道的克隆和表达使得 它们的电生理学和药理学分类。 这些 研究证实，所有这些α 1都是高电压激活的， 渠道 本课题的目的是克隆心脏低电压激活的T细胞， 型钙通道。 令人兴奋的初步研究发现了一种新的 Ca 2+通道基因在心脏中的表达。 假设这个基因 编码T型通道。 该项目的具体目标是：1） 克隆全长cDNA，2）抑制天然T-型 通道在大鼠新生心室肌细胞，3）确定组织 该基因的特异性表达（Northerns和原位杂交，4） 在异源表达系统中表达cDNA，并测量 通道的生物物理性质（单通道电导， 电压依赖性），以及5）确定 表达的电流。 研究设计使用重组DNA 技术从人心脏组织克隆T型通道并表达 非洲爪蟾卵母细胞和HEK-293细胞中克隆的通道。 电生理学方法用于研究表达通道， 单通道和整个细胞水平。 假设是 通过比较克隆通道的属性和观察到的属性进行测试 T型通道中的一种。

Intracellular calcium controls a variety of cellular functions such as contraction, secretion, proliferation, and gene expression. One of the major pathways of calcium influx into cardiac myocytes is through T- and L-type voltage-gated Ca2+ channels. T-type, or low voltage-activated (LVA) channels, open after small depolarizations of the membrane. T-type currents have been found in atrial myocytes and pacemaker cells, where they are involved in determining pacemaker activity. Numerous drugs block L-type channels, however, there are no selective blockers of T-type channels. One of the long-term objectives of this research is to provide an assay system that will allow the development of T-type channel blockers. Calcium channels are multisubunit complexes composed of a large, ion-conducting subunit, alpha1, and several accessory subunits(alpha 2delta, beta and gamma). Six genes encoding alpha1 subunits have been cloned. Cloning and expression of channels has allowed their electrophysiological and pharmacological classification. These studies established that all of these alpha1s are high voltage-activated channels. The aim of this project is to clone the cardiac low voltage-activated T- type Ca2+ channel. Exciting preliminary studies have identified a novel Ca2+ channel gene expressed in heart. The hypothesis is that this gene encodes a T-type channel. The specific aims of this project are to: 1) clone the full-length cDNA, 2) suppress the expression of native T-type channels in rat neonatal ventricular myocytes, 3) determine the tissue specific expression of this gene (Northerns and in situ hybridizations, 4) express the cDNA in heterologous expression systems and measure the biophysical properties of the channel (single channel conductance, voltage-dependence), and 5) determine the pharmacological properties of the expressed current. The research design uses recombinant DNA techniques to clone T-type channels from human heart tissue and express the cloned channels in both Xenopus laevis oocytes and HEK-293 cells. Electrophysiological methods are used to study the expressed channel at both the single channel and whole cell level. The hypothesis will then be tested by comparing the properties of the cloned channel to that observed from T-type channels in isolated cells.