Krnjević K, Morris M E, Reiffenstein R J
Can J Physiol Pharmacol. 1982 Dec;60(12):1643-57. doi: 10.1139/y82-243.
In urethane-anaesthetized rats, ion-selective microelectrodes recorded changes in extracellular K+ and Ca2+ concentrations (delta[K+]omicron and delta[Ca2+]omicron) in pyramidal layers of the hippocampus (mostly in area CA1), which were evoked by fimbrial-commissural stimulation. [K+]omicron increased linearly with frequency of stimulation up to a critical frequency, in the range of 2-5 Hz, where bursts of population spikes appeared, and then rose rapidly to reach a ceiling of 9-12 mM. During continued stimulation, [K+]omicron remained well above the resting level of about 3.0 mM. At the end of stimulation [K+]omicron returned to the base line with a half time of 4-8 s, and a minor undershoot of congruent to 0.5 mM was detectable for 1-2 min. When stimulating at frequencies above the critical value, a sharp fall in [Ca2+]omicron (by an average of one-third below the mean resting level of 1.4 mM) consistently started 1-5 s after the onset of the rapid phase of delta[K+]omicron. [Ca2+]omicron typically reached a minimum in 5-10 s and immediately started to return towards the base line. The recovery of [Ca2+]omicron was often accelerated by an overshoot of up to 0.3 mM; this was followed by a delayed phase of low [Ca2+]omicron for another 2-3 min. During prolonged stimulation at frequencies near 7 Hz, both [Ca2+]omicron and [K+]omicron fluctuated periodically, in time with the appearance and disappearance of bursts of population spikes. Comparable observations were made in area CA2-3 (just external to CA1); in the deeper areas of CA3, in CA4, and in the dentate gyrus, major changes in [K+]omicron and [Ca2+]omicron (as well as bursts of population spikes) were evoked only by prolonged fimbrial stimulation at higher frequencies (congruent to 10 Hz). Thus, although adequate repetitive stimulation of fimbrial-commissural inputs evokes sharp but opposite changes in [K+]omicron and [Ca2+]omicron, the fall in [Ca2+]omicron is consistently much briefer than the rise in [K+]omicron, presumably because of the evanescent character of postsynaptic Ca2+ spikes.
在氨基甲酸乙酯麻醉的大鼠中，离子选择性微电极记录了海马锥体细胞层（主要在CA1区）细胞外K⁺和Ca²⁺浓度的变化（Δ[K⁺]₀和Δ[Ca²⁺]₀），这些变化由穹窿 - 连合刺激诱发。[K⁺]₀随刺激频率线性增加，直至达到临界频率（2 - 5Hz范围），此时出现群体峰电位爆发，然后迅速上升至9 - 12mM的上限。在持续刺激期间，[K⁺]₀保持在远高于约3.0mM的静息水平之上。刺激结束时，[K⁺]₀以4 - 8秒的半衰期回到基线，并且在1 - 2分钟内可检测到约0.5mM的轻微下冲。当以高于临界值的频率刺激时，[Ca²⁺]₀在Δ[K⁺]₀快速上升阶段开始后1 - 5秒持续急剧下降（平均比1.4mM的平均静息水平低三分之一）。[Ca²⁺]₀通常在5 - 10秒内达到最小值并立即开始向基线恢复。[Ca²⁺]₀的恢复常因高达0.3mM的上冲而加速；随后是低[Ca²⁺]₀的延迟阶段，持续另外2 - 3分钟。在接近7Hz的频率下长时间刺激期间，[Ca²⁺]₀和[K⁺]₀都随群体峰电位爆发的出现和消失而周期性波动。在CA2 - 3区（CA1区外侧）也有类似观察结果；在CA3更深区域、CA4和齿状回中，只有通过更高频率（约10Hz）的长时间穹窿刺激才能诱发[K⁺]₀和[Ca²⁺]₀的主要变化（以及群体峰电位爆发）。因此，尽管对穹窿 - 连合输入进行充分的重复刺激会诱发[K⁺]₀和[Ca²⁺]₀急剧但相反的变化，但[Ca²⁺]₀的下降始终比[K⁺]₀的上升短暂得多，这可能是由于突触后Ca²⁺峰电位的短暂特性。
