Protoplasmic Contraction of Paramecium

Abstract

A primitive form of contraction in Paramecium is described. Two factors independent of each other are found to constitute the stimulation, an increase in Ca ions and an increase in OH ions within the cell. The effect common to these two factors is considered to produce a diminution of the intracellular free phosphate ions. It is probably not the absolute concentration of the diminished phosphate but the rate of diminution that is effective for the initiation of contraction. This conclusion is exactly the same as that offered in a previous paper to account for a similar sort of reaction observed in amphibian skeletal muscle. In electrical stimulation, a local contraction is established as a result of polar excitation. It seems reasonable to account for the polar contraction also by the diminution of intracellular free phosphate. Under a special condition, reversal of the polar excitation is induced. This modification seems to be due to the suppressed permeability of the cell membrane to Ca ions and attributable to the shift of the pole at which the concentration of phosphate ions is reduced.