Meuth Sven G, Kanyshkova Tatyana, Meuth Patrick, Landgraf Peter, Munsch Thomas, Ludwig Andreas, Hofmann Franz, Pape Hans-Christian, Budde Thomas
Neurologische Klinik, Bayerische Julius-Maximilians-Universität, Würzburg, Germany.
J Neurophysiol. 2006 Sep;96(3):1517-29. doi: 10.1152/jn.01212.2005. Epub 2006 Jun 7.
By combining molecular biological, electrophysiological, immunological, and computer modeling techniques, we here demonstrate a counterbalancing contribution of TASK channels, underlying hyperpolarizing K+ leak currents, and HCN channels, underlying depolarizing Ih, to the resting membrane potential of thalamocortical relay (TC) neurons. RT-PCR experiments revealed the expression of TASK1, TASK3, and HCN1-4. Quantitative determination of mRNA expression levels and immunocytochemical staining demonstrated that TASK3 and HCN2 channels represent the dominant thalamic isoforms and are coexpressed in TC neurons. Extracellular acidification, a standard procedure to inhibit TASK channels, blocked a TASK current masked by additional action on HCN channels. Only in the presence of the HCN blocker ZD7288 was the pH-sensitive component typical for a TASK current, i.e., outward rectification and current reversal at the K+ equilibrium potential. In a similar way extracellular acidification was able to shift the activity pattern of TC neurons from burst to tonic firing only during block of Ih or genetic knock out of HCN channels. A single compartmental computer model of TC neurons simulated the counterbalancing influence of TASK and HCN on the resting membrane potential. It is concluded that TASK3 and HCN2 channels stabilize the membrane potential by a mutual functional interaction, that the most efficient way to regulate the membrane potential of TC neurons is the converse modulation of TASK and HCN channels, and that TC neurons are potentially more resistant to insults accompanied by extracellular pH shifts in comparison to other CNS regions.
通过结合分子生物学、电生理学、免疫学和计算机建模技术，我们在此证明了TASK通道（构成超极化钾离子泄漏电流）和HCN通道（构成去极化Ih电流）对丘脑皮质中继（TC）神经元静息膜电位的平衡作用。逆转录聚合酶链反应（RT-PCR）实验揭示了TASK1、TASK3和HCN1 - 4的表达。mRNA表达水平的定量测定和免疫细胞化学染色表明，TASK3和HCN2通道是丘脑的主要亚型，并且在TC神经元中共表达。细胞外酸化是抑制TASK通道的标准方法，它阻断了一种被对HCN通道的额外作用所掩盖的TASK电流。只有在存在HCN阻滞剂ZD7288的情况下，才出现了TASK电流典型的pH敏感成分，即外向整流和在钾离子平衡电位处的电流反转。类似地，只有在阻断Ih电流或通过基因敲除HCN通道时，细胞外酸化才能将TC神经元的活动模式从爆发式放电转变为紧张性放电。TC神经元的单室计算机模型模拟了TASK和HCN对静息膜电位的平衡影响。得出的结论是，TASK3和HCN2通道通过相互的功能相互作用稳定膜电位，调节TC神经元膜电位的最有效方法是对TASK和HCN通道进行反向调节，并且与其他中枢神经系统区域相比，TC神经元可能对伴随细胞外pH值变化的损伤更具抵抗力。
