Mackie G O, Meech R W
Nature. 1985;313(6005):791-3. doi: 10.1038/313791a0.
Aglantha digitale is a jellyfish (order Hydromedusae) capable of two distinct kinds of locomotion; 'slow' swimming which is generated endogenously and is used in fishing behaviour, and 'fast' swimming which is evoked by predators and serves for escape. Both forms of swimming are produced by contraction of the bell-shaped body wall and expulsion of a jet of water from an opening at the base of the animal. During slow swimming, the contractions are weak and the animal moves about 15 mm, roughly one body length, but during a fast swim there is a more violent contraction which can propel the animal five times as far. Both forms of contraction depend on impulses in the eight giant motor axons that synapse directly with the muscle sheet making up the inner surface of the body wall. We report here that the giant motor axons are able to mediate both kinds of activity because they can conduct two different sorts of impulse. Fast swimming requires a rapidly conducted Na+-dependent action potential whereas slow swimming depends on a low amplitude Ca2+ 'spike'. This is the first report of an axon capable of two kinds of impulse propagation and it provides a physiological function for low potential Ca2+ activation.
指状艾氏水母是一种水母（水螅水母目），能够进行两种不同类型的运动；一种是“慢速”游动，由内部产生，用于捕食行为，另一种是“快速”游动，由捕食者引发，用于逃生。这两种游动形式都是通过钟形身体壁的收缩以及从动物基部的开口处喷出一股水流来实现的。在慢速游动时，收缩较弱，动物移动约15毫米，大致为一个身体长度，但在快速游动时，会有更剧烈的收缩，能将动物推进五倍远的距离。这两种收缩形式都依赖于八条巨大运动轴突中的冲动，这些轴突直接与构成身体壁内表面的肌肉片层形成突触。我们在此报告，巨大运动轴突能够介导这两种活动，因为它们可以传导两种不同类型的冲动。快速游动需要快速传导的依赖钠离子的动作电位，而慢速游动则依赖低幅度的钙离子“尖峰”。这是关于能够进行两种冲动传播的轴突的首次报告，它为低电位钙离子激活提供了一种生理功能。
