Shen G Y, Chen W R, Midtgaard J, Shepherd G M, Hines M L
Section of Neurobiology, School of Medicine, Yale University, New Haven, Connecticut 06510, USA.
J Neurophysiol. 1999 Dec;82(6):3006-20. doi: 10.1152/jn.1999.82.6.3006.
In olfactory mitral cells, dual patch recordings show that the site of action potential initiation can shift between soma and distal primary dendrite and that the shift is dependent on the location and strength of electrode current injection. We have analyzed the mechanisms underlying this shift, using a model of the mitral cell that takes advantage of the constraints available from the two recording sites. Starting with homogeneous Hodgkin-Huxley-like Na(+)-K(+) channel distribution in the soma-dendritic region and much higher sodium channel density in the axonal region, the model's channel kinetics and density were adjusted by a fitting algorithm so that the model response was virtually identical to the experimental data. The combination of loading effects and much higher sodium channel density in the axon relative to the soma-dendritic region results in significantly lower "voltage threshold" for action potential initiation in the axon; the axon therefore fires first unless the voltage gradient in the primary dendrite is steep enough for it to reach its higher threshold. The results thus provide a quantitative explanation for the stimulus strength and position dependence of the site of action potential initiation in the mitral cell.
在嗅觉二尖瓣细胞中，双电极膜片钳记录显示，动作电位起始位点可在胞体和远端初级树突之间转换，且这种转换取决于电极电流注入的位置和强度。我们利用二尖瓣细胞模型分析了这种转换背后的机制，该模型利用了来自两个记录位点的限制条件。从胞体 - 树突区域中类似霍奇金 - 赫胥黎的钠钾通道均匀分布以及轴突区域中高得多的钠通道密度开始，通过拟合算法调整模型的通道动力学和密度，以使模型响应与实验数据几乎相同。相对于胞体 - 树突区域，轴突中的负载效应和高得多的钠通道密度相结合，导致轴突中动作电位起始的“电压阈值”显著降低；因此，除非初级树突中的电压梯度足够陡峭，使其达到更高阈值，否则轴突会首先放电。因此，这些结果为二尖瓣细胞中动作电位起始位点对刺激强度和位置的依赖性提供了定量解释。
