Ciliary Movement of Sea-urchin Embryos
摘要
Living matter is constantly in motion: we human beings walk through the repeated contraction and relaxation of leg muscles ; migratory fish swim long way also by the muscle contraction ; a great number of unicellular and multicellular microorganisms swim about through the beating of miniature hairlike appendages called "cilia". To address the unsolved question how cilia are regulated when these microorganisms explore their environment and are successful in life, we studied the ciliary movement of embryos and larvae of sea urchins by means of high-speed video micrography and by computerized analysis of ciliary beating at a high resolution. We found the four stages, E_1 through E_4, in the effective stroke with pauses intervening between one and the next. Serotonin, which has been demonstrated to increase the swimming speed of sea-urchin embryos, reduced reversibly the fluctuation and the length of period of E_4, and hence made the beating more stable and faster than before its application. Dopamine, which is known to decrease the swimming speed, increased the fluctuation and the period of E_4 antagonistically to ser\notonin and, in addition, prolonged the pause between E_1 and E_2 and reduced the rate of angular change in E_3. The potassium ion at higher concentrations than of standard seawater, which will depolarize the cell membrane and known to reduce the swimming speed, and to induce backward swimming in larvae of the pluteus and later stages, modified the beating in a manner similar to dopamine. Pauses between E_2 and E_3 often found in the pluteus stage were lengthened by serotonin and the potassium ion. These findings indicate that the internal motility machinery, i.e., the axoneme, can be regulated by modifying one or more of independently controllable stages of beating including E_1 through E_4 described in the present study.