Balestrino M, Aitken P G, Somjen G G
Brain Res. 1986 Jul 9;377(2):229-39. doi: 10.1016/0006-8993(86)90863-2.
The effects of moderate changes of the concentration of ions on the function of mammalian central nervous tissue have not exactly been determined. We placed tissue slices from rat hippocampal formation in an interface chamber for study in vitro. Extracellular potentials were recorded in stratum radiatum and stratum pyramidale in response to stimuli of varying intensity applied to the Schaffer collateral bundle. The overall input-output relationship of excitatory synaptic transmission was gauged by expressing postsynaptic population spike amplitude as a function of presynaptic volley amplitude. The components of the transmission process were also examined by plotting the maximal rate of rise (slope) of the focally recorded synaptic potential (fEPSP) as a function of presynaptic volley amplitude, and the population spike amplitude as a function of the fEPSP slope. Raising the concentration of K+ from the normal level of 3.5 mM to 5 mM caused an average increase of 48% in the population spike evoked by a given presynaptic volley. This was due to an increased electrical excitability of pyramidal cells, as indicated by an increase of the population spike evoked by a given magnitude of fEPSP. Conversely, lowering [K+]o from 3.5 to 2 mM caused a decrease of the population spike relative to a given magnitude of either the presynaptic volley or the fEPSP. Changing [K+]o within these limits caused no significant change of the fEPSP evoked by a given presynaptic volley. Raising [Ca2+]o from 1.2 to 1.8 mM caused a 35% increase in both the fEPSP and the population spike evoked by a given presynaptic volley, and lowering [Ca2+]o to 0.8 mM caused a decrease of both these functions. The amplitude of the population spikes evoked by given fEPSPs changed surprisingly little (but consistently) when [Ca2+]o was varied within these limits. We conclude that moderate changes of [K+]o influence mainly the electric excitability of hippocampal pyramidal cells, with little effect on transmitter release or on the response of the postsynaptic membrane to transmitter, while moderate changes of [Ca2+]o affect the release of excitatory synaptic transmitter more than they affect postsynaptic membrane function.
离子浓度的适度变化对哺乳动物中枢神经组织功能的影响尚未完全确定。我们将大鼠海马结构的组织切片置于界面小室中进行体外研究。在放射层和锥体细胞层记录细胞外电位，以响应施加于Schaffer侧支纤维束的不同强度刺激。通过将突触后群体峰电位幅度表示为突触前峰电位幅度的函数，来衡量兴奋性突触传递的整体输入-输出关系。还通过绘制局部记录的突触电位（fEPSP）的最大上升速率（斜率）作为突触前峰电位幅度的函数，以及群体峰电位幅度作为fEPSP斜率的函数，来检查传递过程的组成部分。将K⁺浓度从正常的3.5 mM提高到5 mM，会使给定突触前峰电位诱发的群体峰电位平均增加48%。这是由于锥体细胞的电兴奋性增加，这表现为给定幅度的fEPSP诱发的群体峰电位增加。相反，将[K⁺]ₒ从3.5 mM降低到2 mM，会导致相对于给定幅度的突触前峰电位或fEPSP，群体峰电位降低。在这些限度内改变[K⁺]ₒ，不会使给定突触前峰电位诱发的fEPSP发生显著变化。将[Ca²⁺]ₒ从1.2 mM提高到1.8 mM，会使给定突触前峰电位诱发的fEPSP和群体峰电位都增加35%，而将[Ca²⁺]ₒ降低到0.8 mM会使这两种功能都降低。当[Ca²⁺]ₒ在这些限度内变化时，给定fEPSP诱发的群体峰电位幅度变化惊人地小（但很一致）。我们得出结论，[K⁺]ₒ的适度变化主要影响海马锥体细胞的电兴奋性，对递质释放或突触后膜对递质的反应影响很小，而[Ca²⁺]ₒ的适度变化对兴奋性突触递质释放的影响大于对突触后膜功能的影响。
