THE EFFECTS OF 4-AMINOPYRIDINE AND TETRAETHYLAMMONIUM IONS ON NORMAL AND DEMYELINATED MAMMALIAN NERVE-FIBERS
THE EFFECTS OF 4-AMINOPYRIDINE AND TETRAETHYLAMMONIUM IONS ON NORMAL AND DEMYELINATED MAMMALIAN NERVE-FIBERS
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DOI：
10.1113/jphysiol.1981.sp013666
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
SHERRATT, RM
中科院分区：
文献类型：
--
作者：
BOSTOCK, H;SEARS, TA;SHERRATT, RM
4-用氨基吡啶（4AP）和四乙基铵离子（TEA）阻断其他神经膜上的电压依赖性K+通道，研究了正常大鼠和白喉毒素脱髓鞘大鼠脊神经根纤维的神经传导。并与温度的药理作用进行比较。TEA和4AP均能增加正常大鼠背根无髓纤维单相复合动作电位的幅度和时程。4AP对动作电位振幅的增强在1 mM附近最大，并且不容易通过洗涤逆转。在浓度高达50 mM时，TEA的作用较弱且可逆。在正常的背根和腹根中，TEA（20 mM）和4AP（5 mM）对有髓纤维的复合动作电位只有轻度的抑制作用。而峰值振幅的轻微减少和宽度的增加，也发现在单纤维与TEA处理，没有辨别在单纤维暴露于4AP在一个很宽的温度范围。电压依赖性K+通道显然发生在哺乳动物的无髓纤维的显着数量，但不是在节点的郎维耶。用纵向电流分析法研究了先前用白喉毒素治疗引起脱髓鞘的脊神经根。受白喉毒素影响的纤维有一个晚期的外向电流，要么局限于节点，或在连续传导的情况下，沿沿着节间分布，这种外向电流被4 AP特异性阻断。4AP和TEA都增加了大多数单一脱髓鞘纤维发生传导阻滞的温度，因此在某些情况下，在生理温度下阻滞的纤维能够传导。4AP比TEA更有效，但其效果不太一致。K+通道明显存在于变宽的结节和脱髓鞘暴露的节间轴膜中。它们的存在使得TEA和4AP能够克服某些脱髓鞘神经纤维中的传导阻滞。
4-Aminopyridine (4AP) and tetraethylammonium ions (TEA), which block voltage-dependent K+ channels in other nerve membranes, were used to study nerve conduction in fibers of normal rat spinal roots and those demyelinated with diphtheria toxin. The pharmacological actions were compared with those of temperature. Both TEA and 4AP increased the amplitude and duration of the monophasically recorded compound action potentials of non-myelinated fibers in normal rat dorsal roots. Enhancement of the action potential amplitude by 4AP was maximal near 1 mM, and was not readily reversed by washing. At concentrations up to 50 mM the action of TEA was weaker and reversible. In normal dorsal and ventral roots TEA (20 mM) and 4AP (5 mM) had only a mildly depressant action on the compound action potentials of myelinated fibers. Whereas the slight reduction in peak amplitude and increase in width was also found in single fibers treated with TEA, none was discerned in single fibers exposed to 4AP over a wide temperature range. Voltage-dependent K+ channels apparently occur in significant numbers in mammalian non-myelinated fibers, but not at nodes of Ranvier. Spinal roots previously treated with diptheria toxin to cause demyelination were studied by longitudinal current analysis. Fibers affected by diphtheria toxin had a late phase of outward current, either restricted to nodes or, in the case of continuous conduction, distributed along internodes, and this outward current was specifically blocked by 4AP. Both 4AP and TEA increased the temperature at which conduction block occurred in most single demyelinated fibers, so that in some cases fibers blocked at physiological temperatures were enabled to conduct. 4AP was more potent than TEA, but less consistent in its effect. K+ channels are apparently present at widened nodes and in internodal axolemma exposed by demyelination. Their presence enables TEA and 4AP to overcome conduction block in some demyelinated nerve fibers.