Nagano M, Cooke I M
J Neurosci. 1987 Mar;7(3):634-48. doi: 10.1523/JNEUROSCI.07-03-00634.1987.
Spontaneous and evoked electrical activity was recorded intracellularly from somata, axons, and terminal dilatations of an isolated peptidergic neurosecretory system, the X-organ-sinus gland, of the crabs Cardisoma carnifex and Podophthalmus vigil in order to compare their electrical characteristics. Spontaneous impulse activity was present in most penetrations and included irregular and pacemaker-like firing, as well as patterned activity (bursting). Extracellular recording showed that spontaneous impulses and bursting originate in a proximal region of the axon tract. Somata vary from being electrically nonresponsive to having overshooting impulses with a relatively slow rate of rise. Overshooting impulses were consistently recorded from axons and terminals. Regional differences include (1) a longer action potential duration in terminals, (2) ability of axons and terminals but not somata to sustain repetitive firing, (3) presence of depolarizing afterpotentials in axons but of hyperpolarizing afterpotentials in somata and terminals, and (4) occurrence of impulse broadening during repetitive firing in some terminals but not in axons or somata. Somata and terminals sustained reduced and slowed, but regenerative impulses in nominally Na-free saline and showed alterations of waveform in nominally Ca-free salines, while axons showed no regenerative responses in Na-free saline and no change of impulse form in Ca-free saline. Terminal responses in the presence of tetraethylammonium chloride (TEA) (50 mM) or Ba (50 mM) exhibited long depolarized plateaus, while impulses of somata were much less prolonged. Bursts often took the form of impulses superimposed on a depolarized plateau. Bursts could be evoked by single stimuli applied to the axon tract but not by current passed intracellularly. After addition of TTX, axon tract stimulation evoked plateaus without superimposed impulses. Terminals exhibit specialization of their electrical responses by comparison to axons and somata in having long-duration action potentials attributable to participation of Ca, capability of sustained firing, impulse broadening, and channels supporting sustained inward currents, all of which might enhance the admission of Ca for initiation of peptide secretion.
为了比较其电特性，从肉食黄道蟹和警惕性长眼蟹的分离肽能神经分泌系统——X器官-窦腺的胞体、轴突和终末膨大部进行细胞内记录自发和诱发的电活动。大多数记录部位都存在自发冲动活动，包括不规则和起搏器样发放，以及模式化活动（爆发）。细胞外记录表明，自发冲动和爆发起源于轴突束的近端区域。胞体的电反应各不相同，从无电反应到具有上升速率相对较慢的超射冲动。在轴突和终末持续记录到超射冲动。区域差异包括：（1）终末动作电位持续时间更长；（2）轴突和终末能够维持重复发放，但胞体不能；（3）轴突存在去极化后电位，而胞体和终末存在超极化后电位；（4）一些终末在重复发放时出现冲动增宽，但轴突和胞体没有。在名义上无钠的盐溶液中，胞体和终末维持的冲动减小且减慢，但具有再生性，在名义上无钙的盐溶液中波形发生改变，而轴突在无钠盐溶液中无再生反应，在无钙盐溶液中冲动形式无变化。在存在氯化四乙铵（TEA）（50 mM）或钡（50 mM）的情况下，终末反应表现为长时去极化平台，而胞体的冲动延长程度小得多。爆发通常表现为叠加在去极化平台上的冲动形式。对轴突束施加单个刺激可诱发爆发，但细胞内通电流则不能。加入河豚毒素（TTX）后，轴突束刺激诱发无叠加冲动的平台。与轴突和胞体相比，终末的电反应具有特殊性，其动作电位持续时间长，这归因于钙的参与、持续发放能力、冲动增宽以及支持持续内向电流的通道，所有这些可能会增加钙的内流以启动肽分泌。
