Voltage-clamp recordings using a single microelectrode were obtained from pyramidal neurones of the basolateral amygdala (BLA) in slices of the rat ventral forebrain. Slow inward current relaxations during hyperpolarizing voltage steps from a holding potential of -40 mV were identified as the muscarinic-sensitive M-current (IM), a time- and voltage-dependent potassium current previously identified in other neuronal cell types. 2. Activation of IM was voltage dependent with a threshold of approximately -70 mV. At membrane potentials positive to this, the steady-state current-voltage (I-V) relationship showed substantial outward rectification, reflecting the time- and voltage-dependent opening of M-channels. The underlying conductance (gM) also increased sharply with depolarization. 3. The reversal potential for IM was -84 mV in medium containing 3.5 mM K+. This was shifted positively by 27 mV when the external K+ concentration was raised to 15 mM. 4. The time courses of M-current activation and deactivation were fitted by a single exponential. The time constant for IM decay, measured at 24 degrees C, was strongly dependent on membrane potential, ranging from 330 ms at -40 mV to 12 ms at -100 mV. 5. Bath application of carbachol (0.5-40 microM) inhibited IM, as evidenced by the reduction or elimination of the slow inward M-current relaxations evoked during hyperpolarizing steps from a holding potential of -40 mV. The outward rectification of the steady-state I-V relationship at membrane potentials positive to -70 mV was also largely eliminated. The inhibition of IM by carbachol was dose dependent and antagonized by atropine. 6. Carbachol produced an inward current shift at a holding potential of -40 mV that was only partially attributable to inhibition of IM. An inward current shift was also produced by carbachol at membrane potentials negative to -70 mV, where IM is inactive. These effects were dose dependent and antagonized by atropine. They were attributed to the muscarinic inhibition of a voltage-insensitive potassium leak conductance (ILeak). 7. In most cells, carbachol reduced the slope of the instantaneous I-V relationship obtained from a holding potential of -70 mV so that it crossed the control I-V plot at the reversal potential for ILeak. This was found to be -108 mV in 3.5 mM K+ saline, shifting to -66 mV in 15 mM K+ saline.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
使用单微电极进行电压钳记录，从大鼠腹侧前脑切片的基底外侧杏仁核（BLA）锥体细胞获得。从 -40 mV 的钳制电位进行超极化电压阶跃时的缓慢内向电流松弛被识别为毒蕈碱敏感性 M 电流（IM），这是一种先前在其他神经元细胞类型中已识别的时间和电压依赖性钾电流。2. IM 的激活是电压依赖性的，阈值约为 -70 mV。在高于此的膜电位下，稳态电流 - 电压（I - V）关系显示出明显的外向整流，反映了 M 通道的时间和电压依赖性开放。基础电导（gM）也随着去极化而急剧增加。3. 在含有 3.5 mM K⁺ 的培养基中，IM 的反转电位为 -84 mV。当外部 K⁺ 浓度提高到 15 mM 时，该电位正向移动 27 mV。4. M 电流激活和失活的时间进程由单个指数拟合。在 24℃ 测量的 IM 衰减时间常数强烈依赖于膜电位，范围从 -40 mV 时的 330 ms 到 -100 mV 时的 12 ms。5. 浴槽应用卡巴胆碱（0.5 - 40 μM）抑制 IM，这可通过从 -40 mV 的钳制电位进行超极化阶跃时诱发的缓慢内向 M 电流松弛的减少或消除来证明。在高于 -70 mV 的膜电位下，稳态 I - V 关系的外向整流也基本消除。卡巴胆碱对 IM 的抑制呈剂量依赖性，并被阿托品拮抗。6. 卡巴胆碱在 -40 mV 的钳制电位下产生内向电流偏移，这仅部分归因于对 IM 的抑制。卡巴胆碱在低于 -70 mV 的膜电位下也产生内向电流偏移，此时 IM 无活性。这些效应呈剂量依赖性，并被阿托品拮抗。它们归因于毒蕈碱对电压不敏感的钾泄漏电导（ILeak）的抑制。7. 在大多数细胞中，卡巴胆碱降低了从 -70 mV 的钳制电位获得的瞬时 I - V 关系的斜率，使其在 ILeak 的反转电位处与对照 I - V 图相交。发现在 3.5 mM K⁺ 盐溶液中该电位为 -108 mV，在 15 mM K⁺ 盐溶液中移至 -66 mV。（摘要截断于 400 字）
