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Quantitative study of mutual relationships involving Ca channel, cytosolic Ca concentration, Na-Ca exchange and Na-K ATPase

Ca通道、胞质Ca浓度、Na-Ca交换和Na-K ATP酶相互关系的定量研究

基本信息

批准号：
62490020
负责人：
YASUI Syozo
金额：
$ 1.79万
依托单位：
KYUSHU INSTITUTE OF TECHNOLOGY (1988)Okazaki National Research Institutes (1987)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

Excitation of neuronal and muscular cells is triggered by depolarization-induced Ca^<2+> entry to the cytoplasm. The release of neurotransmitter substance from presynaptic terminals is mediated by similar mechanisms. As such, Ca^<2+> is an internal messenger, with its cytosolic concentration normally maintained at the submicromolar level. The Ca buffering can be subserved by cytoplasmic ca ion stores. No less important for the Ca regulation is the Na-Ca exchange machinery that excludes calcium ions by letting Na ions move into the cell. The passive Na influx may also result from voltage-gated as well as drug-operated channels. Thus. Na ions also need to be expelled. This physiologic demand is fulfilled by the Na-K pump. This study was done in the context of intracellular ion homeostasis recaputulated above.Voltage clamp experiments using patch pippete were made on solitary horizontal cells isolated enzymatically from the goldfish retina. Since the physiological dynamic range of these non-spiking second-order visual neurons overlaps the membrane voltage region that activates the voltage-gated Ca channel, some mechanism needs to exist to drive out Ca ions. A series of experiments involving the Co test and Na-free substitution showed that the Ca extrusion is subserved by the Na-Ca exchanger. Another set of experiments including by caffeine application indicated the presence of internal calcium stores having a storage capacity of as much as several mM. In this regard, the endplasmic reticulum probably plays a major role. Some regulatory system is required with respect to Na ions as well, to compensate for three types of Na influx: TTX-sensitive one, the Na-Ca exchange component and synaptic current mediated by an excitatory neurotransmitter from photoreceptor terminals. the Ns-KATP ase ope rates for this requirement. Evidence being provided by an ouabain experiment.

神经元和肌肉细胞的兴奋是由去极化诱导的Ca^<2+>进入细胞质触发的。神经递质物质从突触前末梢的释放是由类似的机制介导的。因此，Ca^2+是一种内部信使，其胞质浓度通常维持在亚微摩尔水平。细胞质内的钙离子库可维持钙缓冲作用。对钙调节同样重要的是钠钙交换机制，它通过让钠离子进入细胞来排除钙离子。被动钠内流也可能是由电压门控以及药物操作的通道。就这样。Na离子也需要被排出。这一生理需求由Na-K泵来满足。本研究是在上述细胞内离子稳态的背景下进行的，用膜片钳对酶法分离的金鱼视网膜水平细胞进行电压钳实验。由于这些非尖峰二级视觉神经元的生理动态范围与激活电压门控Ca通道的膜电压区域重叠，因此需要存在某种机制来驱逐Ca离子。一系列的实验包括钴试验和无钠取代实验表明，钠钙交换剂有利于钙的挤出。另一组实验，包括咖啡因的应用表明存在内部钙存储具有高达几个毫米的存储容量。在这方面，内质网可能发挥了重要作用。钠离子也需要一些调节系统，以补偿三种类型的钠内流：TTX敏感的钠内流、钠钙交换成分和由来自感光末梢的兴奋性神经递质介导的突触电流。Ns-KATP酶的活性与此需求有关。哇巴因实验提供的证据。