L-Glutamate-induced membrane hyperpolarization and behavioural responses inParamecium tetraurelia

Summary Paramecium tetraurelia is attracted to L-glutamic acid concentrations of 10^–9M to 10^–4M in a behavioural assay. Electrophysiological studies show thatP. tetraurelia responds to L-glutamate application with hyperpolarization. This response is transient, even in the continued presence of the stimulus. The concentration dependence of the membrane potential response is similar to that of the behavioural responses, although the threshold concentration of L-glutamate required for hyperpolarization is three orders of magnitude lower than for attraction. The membrane potential response to L-glutamate persists following artificial deciliation ofP. tetraurelia.While application of L-glutamate toP. tetraurelia invariably elicits a hyperpolarization, withdrawal of the stimulus frequently results in a second transient membrane response, in the form of either a hyperpolarization or a depolarization. It is suggested that these off-responses may have a significant role in maintaining a behavioural response to L-glutamate.Abbreviation I_che index of chemokinesis