生物の自発性の源について : ゾウリムシの場合

Abstract

Single cell organisms such as Paramecium swim in water by beating of a large number of cilia on the cell membrane. They change the swimming direction spontaneously by partial and transient reversal of cilia beating. The signal for the reversal is an electric pulse across the membrane. Its origin is simple thermal fluctuation of protein molecules of ion channels in the membrane, which produces the electric field fluctuation. It is amplified via the circular ionic current across the membrane. Then, the electric-pulse is generated by field-sensitive channels. The whole process is not deterministic but stochastic. The average time interval of the direction change depends on the population density of swimming cells, although its mechanism is not yet made clear. Finally discussions are made on the meaning of "spontaneous" and a possible relationship is suggested between the spontaneous activity of single cell organisms and our“free will."