Membrane Potential Responses to Thermal Stimulation and the Control of Thermoaccumulation in Paramecium Caudatum

Abstract

The overall membrane potential response of the ciliate Paramecium caudatum to a rise in the temperature of its environment was depolarizing when the ambient temperature before stimulation (Te) was equal to or higher than the culture temperature (Tc), but hyperpolarizing when Te was lower than Tc. The anterior region of the cell responded to a rise in temperature with a localized membrane depolarization. The posterior region was depolarized when Te was equal to or higher than Tc, but hyperpolarized when Te was lower than Tc. The Te-dependent polarity reversal of the posterior response was responsible for the comparable reversal of the overall response. The temperature at which the polarity reversal of the posterior response took place shifted according to Tc. This shift caused a comparable shift in the temperature at which polarity reversal occurred for the overall response. The Tc -dependent polarity reversal of the posterior response and its Tc-dependence are major causes of thermoaccumulation mediated by ciliary activity of Paramecium in regions with temperatures close to Te.