Minami T, Oomura Y, Sugimori M
J Physiol. 1986 Nov;380:145-56. doi: 10.1113/jphysiol.1986.sp016277.
The difference between the ionic bases for electroresponsiveness in the three types of neurone in the ventromedial hypothalamic nucleus (v.m.h.) were studied in in vitro brain slice preparations of the guinea-pig. The current-voltage relationships in all three types of neurone showed anomalous rectification. Application of tetrodotoxin (TTX) abolished the fast action potentials in all three types of cell. In type A cells, injections of outward current pulses did not evoke spikes when the cells were perfused with TTX alone, but the addition of tetraethylammonium chloride elicited broad spikes. In type B and C cells, broad spikes could be evoked with TTX alone. These results suggest the presence of a minimal high-threshold Ca2+ current in type A neurones, and a more prominent one in type B and C neurones. In type B neurones, Ca2+ conductance blockage with Mn2+ or Co2+, or replacement of Ca2+ by Mg2+, abolished the low-threshold response (l.t.r.). Substitution with Ba2+ did not increase the duration of the l.t.r. significantly, suggesting that under normal conditions the falling phase of the response was caused by inactivation of Ca2+ conductance. In type B and C neurones, the amplitude and duration of the after-hyperpolarization (a.h.p.) following direct activation by long outward current pulses were markedly reduced in Ca2+-free solution. These findings indicate that a large component of this response was generated by the Ca2+-dependent K+ conductance increase. In type A cells the a.h.p. amplitude was originally small and was not affected by the above treatment, suggesting that the participation of this conductance was minimal in this type. In type C neurones, the membrane potential following an inward current pulse showed a delayed return to the base line. This delay was produced by transient K+ conductance, since it was reduced by 4-aminopyridine. The frequency-current (f-I) relation of the first interval in type A and C cells was scarcely affected in Ca2+-free solution, while the slope of the initial firing f-I curves in type B neurones which had the l.t.r. became flatter. Furthermore, the f-I curves of the third interval in type C cells became steeper in Ca2+-free solution. The data indicate that the distinct membrane characteristics related to the heterogeneity among cells in the v.m.h. can be attributed to their specific ionic mechanisms, with the type A neurones showing a minimal high-threshold Ca2+ current, the type B having l.t.r. and the type C having a transient K+ (IA) current.
利用豚鼠的体外脑片制备物，研究了腹内侧下丘脑核（v.m.h.）中三种类型神经元电反应性的离子基础差异。所有三种类型神经元的电流-电压关系均显示出反常整流。应用河豚毒素（TTX）可消除所有三种类型细胞中的快速动作电位。在A型细胞中，当细胞仅用TTX灌注时，注入外向电流脉冲不会引发动作电位，但添加四乙铵氯化物会引发宽动作电位。在B型和C型细胞中，仅用TTX就能引发宽动作电位。这些结果表明，A型神经元中存在最小的高阈值Ca2+电流，而B型和C型神经元中这种电流更显著。在B型神经元中，用Mn2+或Co2+阻断Ca2+电导，或用Mg2+替代Ca2+，会消除低阈值反应（l.t.r.）。用Ba2+替代并不会显著增加l.t.r.的持续时间，这表明在正常情况下，反应的下降相是由Ca2+电导的失活引起的。在B型和C型神经元中，在无Ca2+溶液中，由长时间外向电流脉冲直接激活后超极化（a.h.p.）的幅度和持续时间显著减小。这些发现表明，这种反应的很大一部分是由Ca2+依赖性K+电导增加产生的。在A型细胞中，a.h.p.幅度最初较小，且不受上述处理的影响，这表明这种电导在该类型细胞中的参与程度最小。在C型神经元中，内向电流脉冲后的膜电位显示出延迟回到基线。这种延迟是由瞬时K+电导产生的，因为它会被4-氨基吡啶降低。在无Ca2+溶液中，A型和C型细胞第一个间隔的频率-电流（f-I）关系几乎不受影响，而具有l.t.r.的B型神经元初始放电f-I曲线的斜率变得更平缓。此外，在无Ca2+溶液中，C型细胞第三个间隔的f-I曲线变得更陡峭。数据表明，与v.m.h.中细胞异质性相关的独特膜特性可归因于它们特定的离子机制，A型神经元显示出最小的高阈值Ca2+电流，B型具有l.t.r.，C型具有瞬时K+（IA）电流。
