Changes in Membrane Potential during Adaptation to External Potassium Ions in Paramecium Caudatum

Abstract

When Paramecium are transferred from the solution to which they have been adapted to a solution of a different K+ concentration, they initially change their swimming behaviour and then gradually recover normal swimming. This adaptation to the new solution takes 2–3 h. We found that in the process of adaptation there was a change in membrane potential: transfer of the cells to a lower K+ concentration caused depolarization of the potential, whereas transfer to a higher concentration produced a hyperpolarization. In both cases, the change in potential was followed by a gradual repolarization to the original value in the control solution. During adaptation, the intracellular concentration of K+ did not change much. It is probable that the cells change their membrane potential towards a constant level by controlling the membrane conductance for K+.