Lancaster B, Adams P R
J Neurophysiol. 1986 Jun;55(6):1268-82. doi: 10.1152/jn.1986.55.6.1268.
A single-electrode voltage-clamp technique was employed on in vitro hippocampal slices to examine the membrane current responsible for the slow afterhyperpolarization (AHP) in CA1 pyramidal cells. This was achieved by using conventional procedures to evoke an AHP in current clamp, followed rapidly by a switch into voltage clamp (hybrid clamp). The AHP current showed a dependence on extracellular K+, which was close to that predicted for a K+ current by the Nernst equation. The AHP current could be blocked by Cd2+ or norepinephrine. Although the AHP current showed a requirement for voltage-dependent Ca2+ entry, the current did not show any clear intrinsic voltage dependence. Once activated, AHP current is not turned off by hyperpolarizing the membrane potential. The effects of norepinephrine, Cd2+, and tetraethylammonium (TEA) were used to identify an AHP current component to the outward current evoked by depolarizing voltage commands from holding potentials that approximate to the resting potential for these cells. The AHP current can contribute significantly to the outward current during the depolarizing command. Upon repolarization it is evident as a slow outward tail current. This slow tail current had the same time constant as AHP currents evoked by hybrid clamp. Fast components to the tail currents were also observed. These were sensitive to Cd2+ and TEA. They probably represent a voltage-sensitive gKCa, sometimes termed C-current. The strong sensitivity to voltage and TEA displayed by the conventionally described gKCa (IC) are properties inconsistent with the AHP. It seems likely that the AHP current (IAHP) represents a Ca2+-activated K+ current separate from IC and that these two currents coexist in the same cell.
采用单电极电压钳技术，对体外海马脑片进行研究，以检测CA1锥体神经元中负责慢后超极化（AHP）的膜电流。具体操作是先使用传统方法在电流钳模式下诱发AHP，然后迅速切换至电压钳模式（混合钳模式）。AHP电流表现出对细胞外K⁺的依赖性，其依赖性与能斯特方程预测的K⁺电流相近。AHP电流可被Cd²⁺或去甲肾上腺素阻断。尽管AHP电流表现出对电压依赖性Ca²⁺内流的需求，但该电流并未表现出明显的固有电压依赖性。一旦被激活，AHP电流不会因膜电位超极化而关闭。利用去甲肾上腺素、Cd²⁺和四乙铵（TEA）的作用，从接近这些细胞静息电位的钳制电位去极化电压指令诱发的外向电流中，识别出一个AHP电流成分。在去极化指令期间，AHP电流可对外向电流有显著贡献。复极化时，它表现为缓慢的外向尾电流。这个缓慢的尾电流与混合钳模式诱发的AHP电流具有相同的时间常数。还观察到尾电流的快速成分。它们对Cd²⁺和TEA敏感。它们可能代表一种电压敏感性钾钙通道电流（gKCa），有时称为C电流。传统描述的gKCa（IC）对电压和TEA的强敏感性与AHP的特性不一致。AHP电流（IAHP）似乎代表一种与IC不同的Ca²⁺激活K⁺电流，且这两种电流共存于同一细胞中。
