Functional relationship between Ca^<2+>-dependent cation channel and Ca^<2+>-permeable channel

它控制着不同的细胞过程，包括肌肉收缩、神经递质释放和其他形式的分泌、基因表达和细胞增殖。为了激发这些细胞反应，跨质膜的Ca^&lt；2+&gt；内流对提高胞内游离Ca^&lt；2+&gt；浓度([Ca^&lt；2+&gt；]_i)有重要作用。除了已知的电压门控钙通道和钙离子通透性配体门控通道外，由GTP结合蛋白(G蛋白)偶联受体下游激活的钙离子通透性阳离子通道也被认为是主要的跨膜途径之一。了解这些哺乳动物钙离子通透性阳离子通道的分子基础的一个重要线索来自于果蝇视觉转导级联的发现，因为一些钙通透性阳离子通道可能是由果蝇阳离子通道Trp(瞬时受体电位的基因产物)的哺乳动物同系物形成的。使用常规的全细胞模式膜片钳技术和Axopatch 200B放大器在室温下记录了HEK细胞表达TRP3或TRP5的电流。ATP0.1 mM分别在-50 mV诱导表达TRP3和TRP5的HEK细胞产生TRP3和TRP5通道电流。在表达TRP5的HEK细胞中，在不加ATP的情况下，细胞外钙离子以10 mM诱导电流。TRP3通道的电流-电压(I-V)关系是线性的，而TRP5通道的电流-电压(I-V)关系在负电位下向外整流。钙离子对TRP5通道具有通透性，对TRP5通道具有调节作用。

Ca^<2+> controls diverse cellular processes, which include muscle contraction, neurotransmitter release and other forms of secretion, gene expression, and cell proliferation. To evoke these cellular responses, Ca^<2+> influx across the plasma membrane makes a major contribution to augmenting the cytosolic free Ca^<2+> concentration ([Ca^<2+>]_i). In addition to the well-characterized voltage-gated Ca^<2+> channels and Ca^<2+>-permeable ligand-gated channels, Ca^<2+>-permeable cation channels, activated by downstream of GTP binding protein (G-protein) coupled receptors, have been recognized to be one of the major transmembrane pathways. An important clue to understand the molecular basis of these mammalian Ca^<2+>-permeable cation channels came from the findings of Drosophila visual transduction cascade, since some of the Ca^<2+>-permeable cation channels may be formed by the mammalian homologues of the Drosophila cation channel TRP (the gene product of the transient receptor potential, trp).Currents from HEK cells expressing the TRP3 or the TRP5 were recorded at room temperature using the conventional patch-clamp technique of the whole-cell mode with an Axopatch 200B amplifier. ATP 0.1 mM induced the TRP3 and the TRP5 channel currents at a holding potential of -50 mV in HEK cells expressing the TRP3 and the TRP5, respectively. In the HEK cells expressing the TRP5, extracellular Ca^<2+> at 10 mM induced currents without application of ATP. The current-voltage (I-V) relationships were linear for the TRP3 channel, and outwardly rectified at negative potentials for the TRP5 channel. Ca^<2+> is permeable to TRP5 channel and regulates TRP5 channel.