title: Defective ion regulation in a class of membrane-excitation mutants in Paramecium.
abstract: The "paranoiac" mutants of Paramecium aurelia show prolonged backward swimming in solutions containing Na+, unlike wild-type paramecia, which jerk back and forth in Na+ solutions. The paranoiac mutants in Na+ solutions also show large losses of cellular K+ and large influxes of Na+. Three different paranoiac mutants all show similar defects in ion regulation but to different degrees. Wild-type Paramecium, in contrast, shows no Na+ -dependent loss of cellular K+ and a much smaller Na+ influx. In K+ -containing solutions, there is no difference between wild-type and paranoiac paramecia with respect to their cellular K+ content. The Na+ influx, the K+ loss, and the duration of backward swimming are all proportional to the extracellular Na+ concentration. Electrophysiologically, the backward swimming of the paranoiac mutants corresponds to a prolonged depolarization of the membrane potential, while the backward jerks of wild-type Paramecium correspond to a series of transient depolarizations. We propose that the large Na+ influxes and the large K+ effluxes in paranoiacs occur during the periods of backward swimming, while the membrane is depolarized.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002465:Cell Movement / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials; D009154:Mutation; D010247:Paramecium / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013045:Species Specificity
chemical_list: D012964:Sodium; D011188:Potassium