Pachuau Judith, Martin-Caraballo Miguel
Department of Biology, University of Vermont, Burlington, VT 05405, USA.
Dev Neurobiol. 2007 Dec;67(14):1901-14. doi: 10.1002/dneu.20563.
In this study we have characterized the functional expression of T-type Ca(2+) channels in developing chick nodose neurons, a population of placode-derived sensory neurons innervating the heart and various visceral organs. Voltage-gated Ca(2+) currents were measured using whole cell patch clamp recordings in neurons acutely isolated between embryonic day (E) 7 and E20, prior to hatching. E7 nodose neurons express relatively large high voltage-activated (HVA) Ca(2+) currents. HVA current density progressively increases between E7 and E17. T-type Ca(2+) currents were restricted to a few nodose neurons between E7 and E10 but were present in approximately 60% of nodose neurons by E17. T-type Ca(2+) channels regulate the response of nodose neurons to injection of hyperpolarizing currents, but do not have any effect on the action potential waveform. Nickel ions blocked T-type Ca(2+) currents in a concentration-dependent manner with an IC(50) of 17 microM. The high sensitivity of T-type Ca(2+) channels to nickel blockade combined with sequencing of a partial cDNA suggests that T-type Ca(2+) currents are generated by alpha1H subunits in chick nodose neurons. Steady-state activation and inactivation kinetics were similar to those previously reported for other alpha1H channels in mammalian neurons. Semi-quantitative PCR analysis indicates that alpha1H mRNA was present in chick nodose neurons by E7, suggesting that the functional expression of T-type Ca(2+) channels involves a posttranscriptional mechanism. These findings demonstrate a distinct pattern of T-type Ca(2+) channel functional expression in placode-derived neurons when compared with CNS neurons.
在本研究中，我们对发育中的鸡结节神经元中T型Ca(2+)通道的功能表达进行了表征，鸡结节神经元是一群源自基板的感觉神经元，支配心脏和各种内脏器官。在孵化前，使用全细胞膜片钳记录法测量了胚胎第（E）7天至E20天急性分离的神经元中的电压门控Ca(2+)电流。E7结节神经元表达相对较大的高电压激活（HVA）Ca(2+)电流。HVA电流密度在E7和E17之间逐渐增加。T型Ca(2+)电流在E7和E10之间仅限于少数结节神经元，但到E17时约60%的结节神经元中存在。T型Ca(2+)通道调节结节神经元对超极化电流注入的反应，但对动作电位波形没有任何影响。镍离子以浓度依赖的方式阻断T型Ca(2+)电流，IC(50)为17 microM。T型Ca(2+)通道对镍阻断的高敏感性与部分cDNA测序相结合表明，鸡结节神经元中的T型Ca(2+)电流是由alpha1H亚基产生的。稳态激活和失活动力学与先前报道的哺乳动物神经元中其他alpha1H通道的相似。半定量PCR分析表明，E7时鸡结节神经元中存在alpha1H mRNA，这表明T型Ca(2+)通道的功能表达涉及转录后机制。与中枢神经系统神经元相比，这些发现证明了源自基板的神经元中T型Ca(2+)通道功能表达的独特模式。
