Kojima H, Takahashi T
J Physiol. 1985 Nov;368:627-40. doi: 10.1113/jphysiol.1985.sp015880.
Intracellular recordings were made from motoneurones in the isolated spinal cord of neonatal rats. After action potentials had been abolished by tetrodotoxin (TTX, 10(-6) g/ml), small (approximately 0.4 mV) depolarizing potentials occurred spontaneously in motoneurones at low frequencies (approximately 1.5 Hz). These potentials were detectable only after the intracellular Cl- concentration of motoneurones was raised by using KCl electrodes and most of them were blocked by strychnine, suggesting that they are inhibitory post-synaptic potentials (i.p.s.p.s). These spontaneous i.p.s.p.s under TTX are designated as 'miniature i.p.s.p.s' in order to distinguish them from i.p.s.p.s arising from spontaneous impulse activities of interneurones or afferent fibres. The miniature i.p.s.p.s were still observed after Ca2+ in saline was substituted by Mg2+ or Mn2+. In low Ca2+ and high Mg2+ saline, the amplitude distribution of miniature i.p.s.p.s was essentially the same as in normal saline. The frequency of miniature i.p.s.p.s increased when external Ca2+ concentration was raised. The frequency decreased to about 60% of the control when external Ca2+ was substituted by Mg2+ (2-4 mM), whereas it increased to more than 20-fold when substituted by Mn2+ (3-5 mM). When the external K+ concentration was raised, the frequency of miniature i.p.s.p.s under TTX increased non-linearly with the K+ concentration. The maximum slope in the relation between the log frequency and log K+ concentration was about 3.6. When the osmotic pressure was increased by adding sucrose, miniature i.p.s.p.s increased in frequency. The effect of osmotic pressure was relatively mild compared with that reported for the miniature end-plate potentials (e.p.p.s) in the frog. When the temperature was raised, the frequency of miniature i.p.s.p.s increased. The relation between frequency and temperature fitted approximately to a straight line in Arrhenius plot with a Q10 of about 2.6. These characteristics of the miniature i.p.s.p.s closely resemble those of the miniature e.p.p.s. It is concluded that the miniature i.p.s.p.s recorded in motoneurones are equivalent in nature to the miniature e.p.p.s in neuromuscular junctions, thus reflecting the spontaneous release of quantal packages of the inhibitory transmitter.
在新生大鼠的离体脊髓运动神经元上进行细胞内记录。在用河豚毒素（TTX，10^(-6) g/ml）消除动作电位后，运动神经元以低频（约1.5 Hz）自发出现小的（约0.4 mV）去极化电位。这些电位只有在使用氯化钾电极提高运动神经元细胞内氯离子浓度后才能检测到，并且大多数被士的宁阻断，这表明它们是抑制性突触后电位（i.p.s.p.s）。为了将这些在TTX作用下的自发i.p.s.p.s与由中间神经元或传入纤维的自发冲动活动产生的i.p.s.p.s区分开来，将其称为“微小i.p.s.p.s”。在用镁离子或锰离子替代盐水中的钙离子后，仍可观察到微小i.p.s.p.s。在低钙高镁盐水中，微小i.p.s.p.s的幅度分布与正常盐水中基本相同。当提高细胞外钙离子浓度时，微小i.p.s.p.s的频率增加。当用镁离子（2 - 4 mM）替代细胞外钙离子时，频率降至对照的约60%，而用锰离子（3 - 5 mM）替代时，频率增加至20多倍。当提高细胞外钾离子浓度时，TTX作用下的微小i.p.s.p.s频率随钾离子浓度呈非线性增加。对数频率与对数钾离子浓度关系中的最大斜率约为3.6。当通过添加蔗糖提高渗透压时，微小i.p.s.p.s频率增加。与青蛙微小终板电位（e.p.p.s）报道的情况相比，渗透压的影响相对较小。当温度升高时，微小i.p.s.p.s频率增加。频率与温度的关系在阿累尼乌斯图中大致拟合为一条直线，Q10约为2.6。微小i.p.s.p.s的这些特性与微小e.p.p.s的特性非常相似。得出的结论是，在运动神经元中记录到的微小i.p.s.p.s在本质上等同于神经肌肉接头处的微小e.p.p.s，从而反映了抑制性递质的量子包的自发释放。
