POTASSIUM CURRENTS ROLE IN THE DEVELOPING NERVOUS SYSTEM

电压依赖性表达的发育变化 钾通道对传输有重大影响 神经系统中的电信号。 动作的表型 胚胎两栖动物（非洲爪蟾）脊髓神经元的潜力是 很大程度上由钙和钾的平衡决定 电流。 这种平衡通常会在开发过程中改变，以允许 持续时间较长的早期短暂脉冲期 钙依赖性平台期。 随着钾电流的成熟并占据主导地位 电流平衡，钙依赖平台被抑制， 动作电位变成短暂的、主要依赖于钠的尖峰。 最近的工作表明，编码钾的基因 果蝇和哺乳动物中的通道由一个基因家族组成。 非洲爪蟾 通过降低严格性克隆了钾通道基因 (XSha2) 用果蝇钾通道克隆（Shaker）进行筛选。 它的编码 该区域包含在单个不间断的外显子内。 南方 对非洲爪蟾基因组 DNA 的分析表明存在一个基因家族。 三个具体目标集中于确定一个成员 钾通道基因家族及其组织特异性表达；他们的 功能特性；以及它们在神经系统发育中的作用 通过在胚胎中过度表达或阻断它们的表达来推断。 该研究计划包括应用分子和生理学 钾电流表达发展研究分析 及其在调节神经元兴奋性中的作用。 技术要 所采用的方法包括使用聚合酶链式反应和标准 用于鉴定钾通道的基因组文库筛选 克隆、RNase 保护测定以确定转录物水平 表达，卵母细胞中的功能表达，然后是两个电极 电压钳记录和分子操作导致 发育中胚胎中钾通道转录物的错误表达。 如果兴奋性的发展计划建立在 钾通道的转录、过度表达和阻断水平 转录本应足以分别消除和延长 钙依赖性冲动的早期阶段。 这些遗传 因此，操作将改变细胞内钙的量 通过可兴奋的膜提供给未成熟的神经元。 后续 神经元发育的各个方面可能由早期短暂的指导 细胞内钙含量升高。 这些研究可能表明 连接电活动和神经元的调节机制 差异化。

Developmental changes in the expression of voltage-dependent potassium channels have significant consequences for transmission of electrical signals in the nervous system. The phenotype of the action potential of embryonic amphibian (Xenopus laevis) spinal neurons is determined to a large extent by the balance between calcium and potassium currents. This balance is normally altered during development to permit an early transient period of impulses that have long duration calcium-dependent plateaus. As potassium currents mature and dominate the balance of current, the calcium-dependent plateaus are suppressed and the action potential becomes a brief principally sodium-dependent spike. Recent work has demonstrated that the genes encoding potassium channels in Drosophila and mammals comprise a gene family. A Xenopus potassium channel gene (XSha2) has been cloned by reducing stringency screening with a Drosophila potassium channel clone (Shaker). Its coding region is contained within a single uninterrupted exon. Southern analysis of Xenopus genomic DNA suggests the presence of a gene family. Three specific aims are focussed to identify the members of a potassium channel gene family and their tissue specific expression; their functional properties; and their roles in the developing nervous system as deduced by overexpressing or by blocking their expression in embryos. The research plan consists of applying both molecular and physiological analyses to the study of the development of potassium current expression and its role in regulating neuronal excitability. Techniques to be employed include use of the polymerase chain reaction and standard genomic library screening for the identification of potassium channel clones, RNase protection assays to determine levels of transcript expression, functional expression in oocytes followed by two electrode voltage clamp recordings, and molecular manipulations leading to misexpression of potassium channel transcripts in the developing embryo. If the developmental program of excitability is established at the level of transcription, overexpression and block of potassium channel transcripts should be sufficient to eliminate and prolong, respectively, the early period of calcium dependent impulses. These genetic manipulations will thus alter the amount of intracellular calcium provided to immature neurons by an excitable membrane. Subsequent aspects of neuronal development may be directed by early transient elevations in intracellular calcium. These studies may point to regulatory mechanisms linking electrical activity and neuronal differentiation.