Kuenzi F M, Dale N
School of Biomedical Sciences, University of St. Andrews, St. Andrews, Fife KY16 9TS, United Kingdom.
J Neurosci. 1998 Feb 15;18(4):1602-12. doi: 10.1523/JNEUROSCI.18-04-01602.1998.
The spinal neurons of the Xenopus embryo that participate in the swimming motor pattern possess two kinetically distinct sets of potassium currents: the fast IKf and sodium-dependent IKNa, which together constitute approximately 80% of the outward current; and the slow IKs, which constitutes the remainder. To study their respective roles in cell excitability and the swimming pattern, we have characterized their pharmacological properties. Catechol selectively blocked the fast potassium currents (IC50, approximately 10 microM). The block was voltage-dependent, with partial unblocking occurring at positive voltages. alpha-Dendrotoxin and dendrotoxin-I selectively blocked the slow potassium current. Catechol and the dendrotoxins had different effects on membrane excitability: catechol caused spike broadening but had little effect on repetitive firing, whereas both dendrotoxins markedly increased repetitive firing without affecting spike width. By applying these agents to the whole embryo, we tested the role of the fast and slow currents in motor pattern generation. Catechol had little effect on fictive swimming, suggesting that the fast K+ currents are not critical to circuit operation. However, dendrotoxin disrupted swimming early in the episode and increased the duration of ventral root bursts. The slow K+ current, which is a minor component of the total outward current, thus appears to play an important role in motor pattern generation.
快速钾电流IKf和钠依赖性钾电流IKNa，它们共同构成约80%的外向电流；以及缓慢钾电流IKs，它构成其余部分。为了研究它们在细胞兴奋性和游泳模式中的各自作用，我们对它们的药理学特性进行了表征。儿茶酚选择性地阻断快速钾电流（IC50约为10微摩尔）。这种阻断是电压依赖性的，在正电压下会发生部分解除阻断。α-树突毒素和树突毒素-I选择性地阻断缓慢钾电流。儿茶酚和树突毒素对膜兴奋性有不同影响：儿茶酚导致动作电位增宽，但对重复放电影响不大，而两种树突毒素均显著增加重复放电，且不影响动作电位宽度。通过将这些药物应用于整个胚胎，我们测试了快速和缓慢电流在运动模式产生中的作用。儿茶酚对虚拟游泳影响不大，表明快速钾电流对电路运作并非至关重要。然而，树突毒素在发作早期扰乱游泳，并增加腹根爆发的持续时间。因此，缓慢钾电流作为总外向电流的次要成分，似乎在运动模式产生中起重要作用。
