Arkett S A
Department of Biology, University of Victoria, B.C.
J Neurobiol. 1988 Oct;19(7):612-23. doi: 10.1002/neu.480190704.
The rhythmical ciliary arrest behavior characteristic of the veliger larvae of the prosobranch Calliostoma ligatum develops in a predictable sequence of events. Spontaneous, small-amplitude (1-3 mV) postsynaptic potentials (PSPs) are first recorded intracellularly from prototrochal ciliated cells at about 45 h after fertilization. Prototrochal ciliated cells, which are precursors of the locomotory, preoral ciliated cells of mature veligers, are electrically coupled to each other. Cilia beat continuously and erratically at this stage. PSP amplitude and duration gradually increase with age, and at about 56 h, preoral ciliated cells become electrically excitable. A single regenerative action potential first occurs at this time and causes a velum-wide, ciliary arrest. Between 56 and 72 h, the duration of the depolarizing phase of the preoral ciliated cell action potential decreases, the amplitude increases, and the hyperpolarizing undershoot develops. Preoral ciliated cell action potentials appear to be Ca2+-dependent throughout development. Shortening of the action potential duration and development of the hyperpolarizing undershoot may be due to activation of later developing K+ channels. As veligers become competent to metamorphose, the preoral velar cells and their connections with the body deteriorate.
前鳃类扁玉螺（Calliostoma ligatum）面盘幼虫特有的节律性纤毛停止行为，其发展遵循一系列可预测的事件顺序。在受精后约45小时，首次从原纤毛带的纤毛细胞内记录到自发的、小幅度（1-3毫伏）的突触后电位（PSP）。原纤毛带的纤毛细胞是成熟面盘幼虫运动性口前纤毛细胞的前体，它们彼此电耦合。在此阶段，纤毛持续且不规则地摆动。PSP的幅度和持续时间随年龄逐渐增加，在约56小时时，口前纤毛细胞变得电可兴奋。此时首次出现单个再生动作电位，并导致整个面盘的纤毛停止。在56至72小时之间，口前纤毛细胞动作电位去极化阶段的持续时间缩短，幅度增加，超极化后电位出现。口前纤毛细胞动作电位在整个发育过程中似乎都依赖Ca2+。动作电位持续时间的缩短和超极化后电位的出现可能是由于后期发育的K+通道被激活。当面盘幼虫具备变态能力时，口前的面盘细胞及其与身体的连接会退化。
