Abstract
Paranoiac and related mutants of Paramecium tetraurelia display altered membrane excitability. We describe an extension of behavioral characterizations of the paranoiac, fast-2, and tetraethylammonium-insensitive mutants, comparing in detail their reactions to sodium stimulation under standard culture conditions, when grown at various temperatures and when starved. We also use freeze-fracture electron microscopic techniques to analyze in these stocks the morphology of organized arrays of membrane particles, the ciliary plaques. This group of mutants is diverse, showing differences in behavior under standard culture conditions and different reactions to temperature and starvation stresses. Ciliary plaque morphology is altered in some, but not all, of the mutants. The possibility is discussed that these plaques may be sites of potassium or sodium transport.