Ionic Mechanism of Thermoreception in Paramecium

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Abstract
The localization of thermoreceptors in Paramecium, and the ionic basis of thermoreception, was investigated in posterior and anterior fragments of cells. Transverse section of the animals was used to obtain these fragments, which sealed up and swam actively. In the anterior fragment, an increase in the frequency of directional changes in swimming and depolarization of the membrane was produced by cooling below the temperature of the culture. In the posterior fragment, these effects were produced by wanning above culture temperature. Reversal potentials of these effects were found by injection of constant current to change membrane potential. In the anterior fragment, the reversal potential of the response to cooling was more negative than the resting potential and was potassium-dependent (52 mV/log[K+]o). In the posterior fragment, the reversal potential of the warming response was above resting potential and was primarily calcium-dependent (28 mV/log[Ca2+]o). It is concluded that cooling results in changes in the frequency of directional changes in swimming of Paramecium by causing a transient change in the membrane conductance for potassium, whereas warming produces its effects by a transient change in calcium conductance.