EFFECTS OF CA2-SALINA( AND K+ ON MOTILITY AND PHOTOMOTILITY OF THE MARINE CILIATE FABREA)

Fabrea salina is a motile ciliate marine protozoan belonging to the or der Heterotrichida that shows photomotile reactions. We report here th e results of a study on motility and phototaxis of F. salina exposed t o different Ca2+ and K+ concentrations. Our findings show that concent rations of potassium ions greater than that of the growth medium and c oncentrations of calcium ions lower than that of the growth medium cau se a significant increase in phototactic response, while the cell spee d is not significantly affected. A more thorough analysis shows that t he absolute concentrations of Ca2+ or K+ are not important and that th e phototactic responsiveness depends mainly on the ratio of the K+ con centration to the square root of the Ca2+ (the so-called Ja value), in agreement with the results obtained in other protozoa. Our results ar e tentatively discussed in terms of altered membrane potential or ion channel conductances. (C) 1998 Elsevier Science S.A. All rights reserv ed.