Cold-Sensitive Responses in the Paramecium Membrane

Abstract

A transient depolarization was recorded in response to the cooling of a deciliated Paramecium. The amplitude of the depolarization was almost proportional to the cooling rate. Therefore, the cells are sensitive to the rate of temperature change. The input resistance of the membrane transiently increased during the cooling. When constant current was applied to shift the resting membranepotential to a negative or positive level, the initial depolarization in response to cooling decreased, and the following hyperpolarization during cooling reversed to a gradual depolarization during a positive shift. The potential at which the reversal occurred was independent of K⁺ concentration and was slightly dependent on Ca²⁺ concentration (10 mV/log[Ca²⁺]₀). The amplitude of the initial depolarization decreased with the increase in K⁺ and was not affected by Ca²⁺. These results are discussed in terms of changes in membraneconductances in response to cooling.