The relations between membrane potential and parameters of ciliary beat in free-swimming Paramecium caudatum.

It has been known for many years that electric currents flowing through a suspension of Paramecium modify the beating characteristics of the cilia in such a way that the organisms turn and move towards the cathode (Ludloff, 1895; Jennings, 1906). Jahn (1961) has accounted for this behaviour by supposing that current flows through the cell membrane and either enhances or reverses the normal ciliary beat, depending on the direction of the current. Naitoh & Kaneko (1972) have recently shown that the important parameter in controlling the direction of ciliary beat in models of Paramecium extracted with Triton X-100 is the internal calcium ion concentration, and Eckert (1972) has proposed a unifying theory of bioelectric control of ciliary activity in which the internal calcium concentration is governed by the cell-membrane potential. The response of Paramecium to electric fields can then be understood in terms of a variation in membrane potential causing local changes in the direction and frequency of ciliary beat. This paper describes experiments on Paramecium caudatum in which the normal movement is perturbed by external electric fields. The underlying changes in the parameters of ciliary beat are then deduced and interpreted in terms of changes in membrane potential. This method obviates the need for micro-electrodes which would otherwise be necessary to perturb the membrane potential, and the results furnish a useful check on the reliability of the usual micro-electrode studies.