Du J, Zhang L, Weiser M, Rudy B, McBain C J
Unit on Cellular and Synaptic Physiology, National Institute of Child Health and Human Development, Bethesda, Maryland 20892-4495, USA.
J Neurosci. 1996 Jan 15;16(2):506-18. doi: 10.1523/JNEUROSCI.16-02-00506.1996.
The expression of the voltage-gated K(+)-channel subunit Kv3.1b in the developing hippocampus was determined by immunoblot and immunohistochemical techniques. Kv3.1b protein was detected first at postnatal day (P) 8. The Kv3.1b-immunopositive cell number per tissue section reached a maximum at P14 and was maintained through P40. In contrast, the Kv3.1b protein content of isolated membrane vesicles in immunoblots progressively increased through P40, suggesting an increase in Kv3.1b content per cell throughout this time period. Kv3.1b protein was expressed selectively in the somata, proximal dendrites, and axons of cells lying within or near the pyramidal cell layer, consistent with their being GABAergic inhibitory interneurons. Kv3.1b was present in approximately 80% of parvalbumin-positive interneurons. The developmental onset of Kv3.1b and parvalbumin immunoreactivity was identical. In contrast, Kv3.1b was mostly absent from the subset of somatostatin-positive inhibitory interneurons. Electrophysiological recordings were made from stratum pyramidale interneurons in which morphology and Kv3.1b-positive immunoreactivity were confirmed post hoc. Outward currents had voltage-dependent and biophysical properties resembling those of channels formed by Kv3.1b. The current blocked by low concentrations of 4-aminopyridine (4-AP) showed marked inactivation, suggesting that Kv3.1b may coassemble with other members of the Kv3 subfamily. In current-clamp recordings, concentrations of 4-AP that blocked the current through Kv3.1b channels allowed us tentatively to assign a role to Kv3.1b-containing channels in action-potential repolarization. These data demonstrate that Kv3.1b is regulated developmentally in a specific subpopulation of hippocampal interneurons and that channels containing this subunit may be a major determinant in imparting "fast-spiking" characteristics to these and other cells throughout the central nervous system containing the Kv3.1b subunit.
通过免疫印迹和免疫组织化学技术确定了电压门控钾离子通道亚基Kv3.1b在发育中的海马体中的表达情况。在出生后第8天首次检测到Kv3.1b蛋白。每个组织切片中Kv3.1b免疫阳性细胞数量在出生后第14天达到最大值，并维持到出生后第40天。相比之下，免疫印迹中分离的膜囊泡的Kv3.1b蛋白含量在出生后第40天之前逐渐增加，表明在此期间每个细胞的Kv3.1b含量增加。Kv3.1b蛋白选择性地在位于锥体细胞层内或附近的细胞的胞体、近端树突和轴突中表达，这与它们是γ-氨基丁酸能抑制性中间神经元一致。Kv3.1b存在于约80%的小白蛋白阳性中间神经元中。Kv3.1b和小白蛋白免疫反应性的发育起始时间相同。相比之下，生长抑素阳性抑制性中间神经元亚群中大多不存在Kv3.1b。对锥体层中间神经元进行了电生理记录，事后确认了其形态和Kv3.1b阳性免疫反应性。外向电流具有与由Kv3.1b形成的通道相似的电压依赖性和生物物理特性。低浓度4-氨基吡啶（4-AP）阻断的电流显示出明显的失活，表明Kv3.1b可能与Kv3亚家族的其他成员共同组装。在电流钳记录中，阻断通过Kv3.1b通道电流的4-AP浓度使我们初步确定含Kv3.1b通道在动作电位复极化中的作用。这些数据表明，Kv3.1b在海马体中间神经元的特定亚群中受到发育调控，并且含有该亚基的通道可能是赋予这些细胞以及整个中枢神经系统中含有Kv3.1b亚基其他细胞“快速放电”特性的主要决定因素。
