Nuccitelli R, Poo M M, Jaffe L F
J Gen Physiol. 1977 Jun;69(6):743-63. doi: 10.1085/jgp.69.6.743.
We have studied the pattern of electrical currents through amebas (mainly Chaos chaos) with an ultrasensitive extracellular vibrating probe. Amebas drive both steady currents and current pulses through themselves. Relatively steady current with an average surface density of 0.1-0.2 muA/cm2 enters the rear quarter of an ameba and leaves its pseudopods. Streaming reversals are preceded by changes in this current pattern and the region with the largest new inward current becomes the new tail. Ion substitution studies suggest that some of the steady inward current is carried by calcium ions. Characteristic stimulated pulses of current sometimes follow the close approach of the vibrating probe to the side of an advancing pseudopod. Such a pulse enters the cytoplasm through a small patch of membrane near the probe (and seems to leave through the adjacent membrane), is usually followed by hyaline cap and then by pseudopod initiation, is calcium dependent, lasts about 5-10 s, and has a peak density of about 0.4 muA/cm2. Spontaneous pulses of similar shape and duration may enter or leave any part of an animal. They are much less localized, tend to have higher peak densities, and occur in physiological salt solutions at about 0.2-4 times per minute. Retraction of a pseudopod is always accompanied or preceded by a spontaneous pulse which leaves its sides.
我们用一个超灵敏的细胞外振动探针研究了通过变形虫（主要是大变形虫）的电流模式。变形虫能驱动稳定电流和电流脉冲通过自身。平均表面密度为0.1 - 0.2微安/平方厘米的相对稳定电流进入变形虫的后四分之一部分，并从其伪足流出。在流动逆转之前，这种电流模式会发生变化，新的内向电流最大的区域会成为新的尾部。离子替代研究表明，一些稳定的内向电流是由钙离子携带的。当振动探针靠近前进中的伪足一侧时，有时会出现特征性的刺激电流脉冲。这样的脉冲通过探针附近一小片膜进入细胞质（似乎从相邻的膜流出），通常随后会出现透明帽，然后是伪足起始，它依赖于钙，持续约5 - 10秒，峰值密度约为0.4微安/平方厘米。形状和持续时间相似的自发脉冲可能进入或离开动物的任何部位。它们的定位性差得多，往往具有更高的峰值密度，并且在生理盐溶液中大约每分钟出现0.2 - 4次。伪足的回缩总是伴随着或先于一个从其侧面离开的自发脉冲。
