Cooke I M
J Exp Biol. 1985 Sep;118:1-35. doi: 10.1242/jeb.118.1.1.
Electrical activity recorded intracellularly from peptidergic neurosecretory terminal dilatations in the sinus gland of crabs (principally Cardisoma guanhumi and C. carnifex) is described. Recordings were made from the neurohaemal organ in situ on the neural tissue of the isolated eyestalk and from isolated sinus gland-sinus gland nerve preparations. Verification that electrodes penetrated terminals was obtained by dye marking. Resting potentials ranged between -30 and -80mV. Overshooting action potentials of long duration (5-20 ms at 1/2 amplitude) relative to those of non-secretory axons (less than 2ms) were recorded in approximately 70% of stable penetrations. Action potentials occurred spontaneously at slow (less than 0.2s-1) rates in 75% of penetrations. Sequential intra- and extracellular recordings with the same microelectrode, on the same terminal, indicate impulse generation by the terminal itself. Extracellular stimulation of the axon tract evokes an all-or-none action potential at distinct threshold and latency. At rates of stimulation exceeding 5s-1, discrete fluctuations in the form of responses occur. Similar waveforms occur spontaneously and can be evoked by passing current through the electrode. They are interpreted to be electrotonically recorded activity of other parts of a complex axonal terminal arborization. Some, but not all, terminals exhibit impulse broadening (up to three-fold at 1/2 amplitude) during repetitive firing exceeding 1s-1. The same terminals show reduced impulse duration with hyperpolarization and broadened impulses with imposed depolarization. The changes are due to altered repolarization rates. Terminals sustain steady impulse firing at rates (up to 5s-1) linearly related to the imposed depolarizing current. Regenerative potentials, though of reduced rate of rise and amplitude, can be evoked by depolarizing current passed through the electrode during perfusion with salines having 1/2 normal [Na+], or containing tetrodotoxin (10(-6)moll-1). However, these block axonal conduction. Nominally Ca-free saline causes increased spontaneity and depolarization of about 5 mV in half the preparations examined, but reaching 20 mV in the others, with resultant inactivation of regenerative activity. Impulses in low-Ca saline show alterations of the falling phase, it being faster initially and then slower than normal. Thus, while the action potentials of neurosecretory axons are Na dependent, the terminals support regenerative impulses mediated by both Na and Ca.
本文描述了从蟹（主要是关氏硬壳蟹和食蟹硬壳蟹）窦腺中肽能神经分泌终末膨大处进行细胞内记录的电活动。记录是在离体眼柄神经组织上原位的神经血器官以及分离的窦腺 - 窦腺神经标本上进行的。通过染料标记来验证电极是否穿透了终末。静息电位在 -30 至 -80mV 之间。在大约 70% 的稳定穿透记录中，相对于非分泌性轴突（小于 2ms），记录到了持续时间较长（半幅值时为 5 - 20ms）的超射动作电位。在 75% 的穿透记录中，动作电位以缓慢（小于 0.2s⁻¹）的速率自发出现。用同一微电极在同一终末进行的细胞内和细胞外顺序记录表明，动作电位是由终末自身产生的。对轴突束进行细胞外刺激会在特定阈值和潜伏期引发全或无动作电位。当刺激速率超过 5s⁻¹ 时，会出现离散的反应形式波动。类似的波形会自发出现，并且可以通过使电流通过电极来诱发。它们被解释为复杂轴突终末分支其他部分的电紧张性记录活动。在超过 1s⁻¹ 的重复放电过程中，一些（但不是全部）终末会出现冲动展宽（半幅值时可达三倍）。相同的终末在超极化时冲动持续时间缩短，在去极化时冲动展宽。这些变化是由于复极化速率改变所致。终末能够以与施加的去极化电流呈线性相关的速率（高达 5s⁻¹）维持稳定的冲动发放。在用含 1/2 正常[Na⁺]的生理盐水灌注或含有河豚毒素（10⁻⁶mol·l⁻¹）的情况下，通过电极施加去极化电流可以诱发再生电位，尽管其上升速率和幅度有所降低。然而，这些会阻断轴突传导。在名义上无钙的生理盐水中，大约一半被检查的标本自发性增加且去极化约 5mV，但在其他标本中可达 20mV，导致再生活动失活。在低钙生理盐水中的冲动显示下降相发生改变，最初较快，然后比正常情况慢。因此，虽然神经分泌轴突的动作电位依赖于 Na，但终末支持由 Na 和 Ca 介导的再生冲动。
