Hsiung G R, Puil E
Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
Neuroscience. 1990;37(1):115-25. doi: 10.1016/0306-4522(90)90196-b.
Action potentials recorded in vitro from the perikarya of trigeminal root ganglion neurons (guinea-pig) were examined for their sensitivities to blockers of specific ion channels or to removal of certain ionic species in the bathing media. The majority (approximately 65%) of the 137 neurons exhibited action potentials following application of the Na(+)-channel blocker, tetrodotoxin. This group of neurons was selected for further investigation under conditions of extracellular K(+)-channel blockade with tetraethylammonium and 4-aminopyridine. Long-duration action potentials consisting of two distinct components could be evoked under such conditions. The fast component of the spike was abolished in Na(+)-deficient perfusion media and was sensitive to blockade by extracellular lidocaine or intracellular QX-222 applications. It is likely that the slow component was mediated mainly by Ca2+, but in Ca2(+)-deficient media. Mg2(+)-influx may have contributed to the small voltage response. The amplitude and shape of the slow component was unaffected by applications of lidocaine or QX-222. Self-sustained repetitive firing was also observed in 11 neurons in the above conditions. This activity persisted even under conditions of severe deficiencies in extracellular [Ca2+] or [Na+]. Two distinct but overlapping K(+)-conductances that were sensitive to blockade by internal Cs(+)-application and insensitive to applications of tetraethylammonium and 4-aminopyridine, appear to mediate the afterhyperpolarization of the long-duration spike. One portion of the afterhyperpolarization was 60-150 ms in duration and was unaffected by removal of Ca2+ from the extracellular media, while the other had a time-course lasting 150-250 ms and was abolished by removal of external Ca2+. In some neurons, these K(+)-conductances were blocked by high doses of doxorubicin or cisplatin. The results show that at least two ion species (Na+ and Ca2+) contribute to the formation of the tetrodotoxin-resistant, long-duration action potential in trigeminal root ganglion neurons during selective K(+)-conductance blockade and also provide evidence for Mg2+ involvement in the generation of this voltage response.
对从豚鼠三叉神经根神经节神经元胞体在体外记录的动作电位，检测了它们对特定离子通道阻滞剂或对去除浴液中某些离子成分的敏感性。在应用钠通道阻滞剂河豚毒素后，137个神经元中的大多数（约65%）表现出动作电位。选择这组神经元在细胞外钾通道被四乙铵和4-氨基吡啶阻断的条件下进行进一步研究。在这种条件下可诱发由两个不同成分组成的长时程动作电位。动作电位的快速成分在缺钠灌注液中消失，并且对细胞外利多卡因或细胞内应用QX-222的阻断敏感。慢成分可能主要由Ca2+介导，但在缺钙介质中，Mg2+内流可能对小的电压反应有贡献。慢成分的幅度和形状不受利多卡因或QX-222应用的影响。在上述条件下，在11个神经元中还观察到了自发放电重复发放。即使在细胞外[Ca2+]或[Na+]严重缺乏的条件下，这种活动仍持续存在。两种不同但重叠的钾电导似乎介导了长时程动作电位的超极化后电位，它们对细胞内应用Cs+阻断敏感，而对四乙铵和4-氨基吡啶的应用不敏感。超极化后电位的一部分持续时间为60 - 150毫秒，不受细胞外液中Ca2+去除的影响，而另一部分时程持续150 - 250毫秒，在去除细胞外Ca2+后消失。在一些神经元中，这些钾电导被高剂量的阿霉素或顺铂阻断。结果表明，在选择性钾电导阻断期间，至少两种离子（Na+和Ca2+）有助于三叉神经根神经节神经元中河豚毒素抗性长时程动作电位的形成，并且也为Mg2+参与这种电压反应的产生提供了证据。
