Parri H R, Crunelli V
Physiology Unit, School of Molecular and Medical Biosciences, University of Wales Cardiff, Cardiff CF1 3US, United Kingdom.
J Neurosci. 1998 Feb 1;18(3):854-67. doi: 10.1523/JNEUROSCI.18-03-00854.1998.
The properties of the Na+ current present in thalamocortical neurons of the dorsal lateral geniculate nucleus were investigated in dissociated neonate rat and cat neurons and in neurons from slices of neonate and adult rats using patch and sharp electrode recordings. The steady-state activation and inactivation of the transient Na+ current (INa) was well fitted with a Boltzmann curve (voltage of half-maximal activation and inactivation, V1/2, -29.84 mV and -70.04 mV, respectively). Steady-state activation and inactivation curves showed a small region of overlap, indicating the occurrence of a INa window current. INa decay could be fitted with a single exponential function, consistent with the presence of only one channel type. Voltage ramp and step protocols showed the presence of a noninactivating component of the Na+ current (INaP) that activated at potentials more negative (V1/2 = -56.93 mV) than those of INa. The maximal amplitude of INaP was approximately 2.5% of INa, thus significantly greater than the calculated contribution (0.2%) of the INa window component. Comparison of results from dissociated neurons and neurons in slices suggested a dendritic as well as a somatic localization of INaP. Inclusion of papain in the patch electrode removed the fast inactivation of INa and induced a current with voltage-dependence (V1/2 = -56.92) and activation parameters similar to those of INaP. Current-clamp recordings with sharp electrodes showed that INaP contributed to depolarizations evoked from potentials of approximately -60 mV and unexpectedly to the amplitude and latency of low-threshold Ca2+ potentials, suggesting that this noninactivating component of the Na+ channel population plays an important role in the integrative properties of thalamocortical neurons during both tonic and burst-firing patterns.
运用膜片钳和尖锐电极记录技术，在新生大鼠和猫的离体神经元以及新生和成年大鼠脑片的神经元中，研究了背侧外侧膝状核丘脑皮质神经元中存在的Na⁺电流特性。瞬态Na⁺电流（INa）的稳态激活和失活情况与玻尔兹曼曲线拟合良好（激活和失活的半最大电压，V1/2分别为-29.84 mV和-70.04 mV）。稳态激活和失活曲线显示有一小部分重叠区域，表明存在INa窗电流。INa衰减可拟合为单指数函数，这与仅存在一种通道类型相符。电压斜坡和阶跃方案显示存在一种非失活的Na⁺电流成分（INaP），其在比INa更负的电位（V1/2 = -56.93 mV）时激活。INaP的最大幅度约为INa的2.5%，因此明显大于INa窗成分的计算贡献（0.2%）。对离体神经元和脑片神经元结果的比较表明，INaP在树突和胞体均有定位。在膜片钳电极中加入木瓜蛋白酶可消除INa的快速失活，并诱导出一种具有电压依赖性（V1/2 = -56.92）且激活参数与INaP相似的电流。用尖锐电极进行的电流钳记录表明，INaP有助于从约-60 mV电位诱发的去极化，并且意外地对低阈值Ca²⁺电位的幅度和潜伏期有贡献，这表明Na⁺通道群体的这种非失活成分在丘脑皮质神经元的紧张性和爆发式放电模式的整合特性中起重要作用。
