Cassell J F, Clark A L, McLachlan E M
J Physiol. 1986 Mar;372:457-83. doi: 10.1113/jphysiol.1986.sp016020.
Intracellular recording techniques have been used to determine the electrophysiological properties of sympathetic neurones in ganglia of the caudal lumbar sympathetic chain (l.s.c.) and in the distal lobes of inferior mesenteric ganglia (i.m.g.) isolated from guinea-pigs. Passage of suprathreshold depolarizing current initiated transient bursts of action potentials in 97% of l.s.c. neurones, but only 13% of i.m.g. cells ('phasic' neurones). Most i.m.g. neurones fired continuously during prolonged depolarizing pulses ('tonic' neurones). Passive membrane properties varied; mean cell input resistance was similar between groups, but phasic neurones had smaller major input time constants on average than had tonic cells. Current-voltage relations determined under both current clamp and voltage clamp were linear around resting membrane potential (approximately 60 mV), where membrane conductance was lowest. Instantaneous and time-dependent rectification varied in the different neurone types. The current underlying the after-hyperpolarization following the action potential was significantly larger on average in tonic i.m.g. cells than in phasic neurones, although its time course (tau = 100 ms) was similar. Phasic neurones fired tonically when depolarized after adding the muscarinic agonist, bethanechol (10(-5) M to 10(-4) M), to the bathing solution. Bethanechol blocked a proportion of the maintained outward current (presumably the M-current, IM, Adams, Brown & Constanti, 1982) in phasic neurones; this current was small or absent in tonic neurones. Transient outward currents resembling the A-current (IA, Connor & Stevens, 1971 a) were evoked in tonic but not in phasic neurones by depolarization from resting membrane potential. IA could only be demonstrated in phasic neurones after a period of conditioning hyperpolarization. After a step depolarization to approximately --50 mV, IA reached peak amplitude at about 7 ms and then decayed with a time constant of about 25 ms in both neurone types. Activation characteristics of IA were similar for phasic and tonic neurones, but inactivation curves, although having the same shape, were shifted to more depolarized voltages in tonic neurones. That is, IA was largely inactivated at resting membrane potential in phasic, but not tonic neurones. It is concluded that the discharge patterns of the two populations of sympathetic neurones result from differences in the voltage-dependent potassium channels present in their membranes. The anatomical occurrence of the different cell types suggests that phasic neurones are vasoconstrictor and tonic neurones are involved with visceral motility.
细胞内记录技术已被用于测定从豚鼠分离出的尾侧腰交感神经链（l.s.c.）神经节和肠系膜下神经节（i.m.g.）远侧叶中交感神经元的电生理特性。阈上去极化电流通过时，97%的l.s.c.神经元引发动作电位的短暂爆发，但i.m.g.细胞中只有13%（“位相性”神经元）如此。大多数i.m.g.神经元在长时间去极化脉冲期间持续放电（“紧张性”神经元）。被动膜特性各不相同；两组之间平均细胞输入电阻相似，但位相性神经元的主要输入时间常数平均比紧张性细胞小。在电流钳制和电压钳制条件下测定的电流-电压关系在静息膜电位（约-60 mV）附近呈线性，此时膜电导最低。不同神经元类型中瞬时整流和时间依赖性整流各不相同。动作电位后超极化所依据的电流在紧张性i.m.g.细胞中平均明显大于位相性神经元，尽管其时间进程（时间常数τ = 100 ms）相似。在位相性神经元中，向浴液中加入毒蕈碱激动剂氨甲酰甲胆碱（10⁻⁵ M至10⁻⁴ M）后去极化时，它们会持续放电。氨甲酰甲胆碱阻断了位相性神经元中一部分持续外向电流（推测为M电流，IM，亚当斯、布朗和康斯坦蒂于1982年提出）；这种电流在紧张性神经元中很小或不存在。从静息膜电位去极化时，紧张性神经元中可诱发类似A电流（IA，康纳和史蒂文斯，1971a）的瞬时外向电流，而位相性神经元中则不会。只有在经过一段时间的预处理超极化后，位相性神经元中才能显示出IA。在向约-50 mV的阶跃去极化后，IA在约7 ms时达到峰值幅度，然后在两种神经元类型中均以约25 ms的时间常数衰减。位相性和紧张性神经元中IA的激活特性相似，但失活曲线虽然形状相同，但在紧张性神经元中向更正的电压偏移。也就是说，在静息膜电位时，IA在很大程度上在位相性神经元中失活，但在紧张性神经元中并非如此。结论是，这两种交感神经元群体的放电模式源于其膜中存在的电压依赖性钾通道的差异。不同细胞类型的解剖学分布表明，位相性神经元是血管收缩神经元，而紧张性神经元与内脏运动有关。
