Funahashi Makoto, Mitoh Yoshihiro, Matsuo Ryuji
Department of Oral Physiology, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8525, Japan.
Brain Res. 2002 Jun 28;942(1-2):31-45. doi: 10.1016/s0006-8993(02)02651-3.
We investigated the electrophysiological properties of the area postrema neurons in acutely prepared rat brain slices using the whole-cell patch-clamp technique. Two different types of transient outward potassium current (I(to)), fast and slow, were found in the area postrema. Both the decay time constant and rise time were significantly faster in the fast I(to) than in the slow I(to). Both current-clamp and voltage-clamp recordings revealed that the activation of fast and slow I(to) contributes to generation of the different spiking patterns, late spiking and interrupted spiking, respectively. The activation and inactivation of both I(to) were strongly voltage-dependent. Curve fitting by the Boltzmann equation revealed no significant difference in the activation and inactivation curves for each I(to) except that the slope factor of inactivation was larger for fast I(to). Both I(to) were suppressed dose-dependently by application of 4-aminopyridine. Each spiking pattern was enhanced when cells were held at a more hyperpolarized membrane potential, i.e. a longer latency of the first spike or longer interspike interval between the first and second spikes. The voltage-dependent modulation of the spiking pattern was consistent with the voltage-dependent activation of I(to). The present study shows significant subdivisions of the area postrema neurons distinguished by a difference in the kinetics of I(to) and spiking patterns. We discuss the role of I(to) as the ionic current underlying neuronal excitability.
我们使用全细胞膜片钳技术，研究了急性制备的大鼠脑片中最后区神经元的电生理特性。在最后区发现了两种不同类型的瞬时外向钾电流（I(to)），即快速型和慢速型。快速I(to)的衰减时间常数和上升时间均显著快于慢速I(to)。电流钳和电压钳记录均显示，快速和慢速I(to)的激活分别有助于产生不同的放电模式，即晚期放电和间断放电。两种I(to)的激活和失活均强烈依赖电压。通过玻尔兹曼方程进行曲线拟合发现，每种I(to)的激活曲线和失活曲线无显著差异，只是快速I(to)的失活斜率因子更大。应用4-氨基吡啶后，两种I(to)均呈剂量依赖性抑制。当细胞保持在更超极化的膜电位时，即第一个动作电位的潜伏期更长或第一个和第二个动作电位之间的峰间间隔更长时，每种放电模式都会增强。放电模式的电压依赖性调制与I(to)的电压依赖性激活一致。本研究表明，最后区神经元存在明显的细分，其区别在于I(to)动力学和放电模式的差异。我们讨论了I(to)作为神经元兴奋性基础离子电流的作用。
