Chiba Chikafumi, Oi Hanako, Saito Takehiko
Life and Environmental Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8572, Japan.
Brain Res Dev Brain Res. 2005 Jan 1;154(1):25-34. doi: 10.1016/j.devbrainres.2004.09.011.
Adult newts can regenerate their entire retinas following a complete removal of the original tissues. During retinal regeneration, ganglion cells differentiate first from the progenitor cells, and develop their capability of spike firing. In the present study, to understand the process of functional differentiation of ganglion cells, we investigated alterations of their voltage-gated sodium currents during retinal regeneration by a whole-cell patch-clamp technique. To minimize space clamp errors, sodium currents were recorded from neurite-free somata of presumptive ganglion cells that were mechanically isolated from living slices of regenerating retinas at different morphological stages. During retinal regeneration, the somatic sodium current density was increased 2.6-fold (48 to 123 pF/pA) and the half-activating voltage was shifted slightly to more hyperpolarizing membrane potentials (-10 to -13 mV), while steady-state inactivation was not changed obviously. Curve fitting analysis of currents revealed that the sodium current consists of two components with different inactivation time constants. During retinal regeneration, the ratio of slow to fast inactivating current component was increased 2.6-fold (0.11 to 0.29). These results suggest that the somatic sodium currents of ganglion cells may undergo modifications of their voltage dependence and kinetic properties during retinal regeneration. A small number of the presumptive ganglion cells in regenerating retinas with a segregating inner plexiform layer exhibited sodium currents comparable to those in the normal retina. This might suggest that maturational regulation of sodium channel function starts during a period of synaptic layer formation within the retina.
成年蝾螈在完全移除原始组织后能够再生其整个视网膜。在视网膜再生过程中，神经节细胞首先从祖细胞分化出来，并发展出产生动作电位的能力。在本研究中，为了了解神经节细胞功能分化的过程，我们通过全细胞膜片钳技术研究了视网膜再生过程中它们电压门控钠电流的变化。为了尽量减少空间钳制误差，从处于不同形态阶段的再生视网膜活切片中机械分离出的假定神经节细胞的无神经突胞体记录钠电流。在视网膜再生过程中，胞体钠电流密度增加了2.6倍（从48 pF/pA增加到123 pF/pA），半激活电压略微向更超极化的膜电位偏移（从-10 mV到-13 mV），而稳态失活没有明显变化。电流的曲线拟合分析表明，钠电流由两个具有不同失活时间常数的成分组成。在视网膜再生过程中，慢失活电流成分与快失活电流成分的比例增加了2.6倍（从0.11增加到0.29）。这些结果表明，在视网膜再生过程中，神经节细胞的胞体钠电流可能会经历电压依赖性和动力学特性的改变。在具有分离的内网状层的再生视网膜中，少数假定的神经节细胞表现出与正常视网膜中相当的钠电流。这可能表明钠通道功能的成熟调节在视网膜内突触层形成期间就开始了。
