Soliven B, Szuchet S, Nelson D J
Department of Neurology, University of Chicago, Illinois 60637.
J Membr Biol. 1991 Nov;124(2):127-37. doi: 10.1007/BF01870457.
The effects of tumor necrosis factor-alpha (TNF-alpha), a cytokine secreted by activated macrophages, on the electrical membrane properties of cultured adult ovine oligodendrocytes (OLGs) were investigated using the whole-cell voltage-clamp technique. Treatment with recombinant human TNF-alpha (rhTNF) for 24 to 72 hr produces (i) process retraction in some but not all OLGs, (ii) a reduction in the resting membrane potential with no significant change in membrane capacitance or input resistance over control cells and (iii) a decrease in the expression of both the inwardly rectifying and outward K+ current. The magnitude of the membrane potential change as well as K+ current inhibition was larger in cells with retracted processes. The electrophysiological effects of rhTNF were attenuated when rhTNF was neutralized with a polyclonal anti-rhTNF antibody. The binding of rhTNF to its receptor has been reported to increase GTP binding, to increase GTPase activity of a pertussis-sensitive G protein, and to produce an elevation in intracellular cAMP in other cell types. However, pretreatment of OLGs with activated pertussis toxin failed to attenuate or mimic the effects of rhTNF. Chronic exposure of OLGs to the membrane permeant analogue of cAMP, 8-bromo-cAMP, resulted primarily in an inhibition of the inwardly rectifying K+ current, an effect which was less than that produced by rhTNF alone and without any of the associated rhTNF-induced morphological changes. This indicates that the effects of rhTNF cannot be entirely accounted for by an elevation in intracellular cAMP. Cycloheximide (CHX), an inhibitor of protein synthesis, mimicked the effects of rhTNF; however, the effects of rhTNF and CHX were not additive. The finding that both ionic current expression and membrane potential were reduced in cells treated with rhTNF that appeared morphologically normal suggests that abnormal ion channel expression in OLGs precedes and may contribute to eventual myelin swelling and damage.
利用全细胞膜片钳技术，研究了活化巨噬细胞分泌的细胞因子肿瘤坏死因子-α（TNF-α）对培养的成年羊少突胶质细胞（OLGs）电膜特性的影响。用重组人TNF-α（rhTNF）处理24至72小时会产生以下结果：（i）部分而非全部OLGs出现突起回缩；（ii）静息膜电位降低，膜电容或输入电阻与对照细胞相比无显著变化；（iii）内向整流钾电流和外向钾电流的表达均减少。突起回缩的细胞中膜电位变化的幅度以及钾电流抑制作用更大。当用多克隆抗rhTNF抗体中和rhTNF时，rhTNF的电生理效应减弱。据报道，rhTNF与其受体的结合会增加GTP结合、增加百日咳敏感G蛋白的GTP酶活性，并在其他细胞类型中导致细胞内cAMP升高。然而，用活化的百日咳毒素预处理OLGs未能减弱或模拟rhTNF的作用。OLGs长期暴露于cAMP的膜通透性类似物8-溴-cAMP主要导致内向整流钾电流受到抑制，这种作用小于单独使用rhTNF所产生的作用，且没有任何rhTNF诱导的相关形态学变化。这表明rhTNF的作用不能完全由细胞内cAMP升高来解释。蛋白质合成抑制剂环己酰亚胺（CHX）模拟了rhTNF的作用；然而，rhTNF和CHX的作用并非相加。在用rhTNF处理且形态正常的细胞中离子电流表达和膜电位均降低，这一发现表明OLGs中异常离子通道表达先于并可能导致最终的髓鞘肿胀和损伤。
