Membrane potential fluctuation in Paramecium.

The fluctuation of the membrane potential in Paramecium caudatum cells was measured. The fluctuation was very large and composed of slow and periodic components and fast and random ones. The power of fast fluctuation depended on the environmental salt condition, particularly on the ratio of the potassium ion concentration to the square root of the calcium ion concentration, [K+]o/[Ca2+]o(1/2), in the medium. The power greatly increased with the decrease of this ratio. The power density spectrum of fluctuation was of the 1/(1 + (f/fc)2) type when the total power was large. There, the fluctuation arose mainly from the local current of potassium ions. Some cooperation among potassium channels to increase the fluctuation was suggested. The spectrum became of the 1/f type when the total power was small.