EFFECT OF EXTRACELLULAR CA2-ANTAGONISTS ON THE MOVEMENT AND CHEMOORIENTATION OF MALE GAMETES OF ECTOCARPUS-SILICULOSUS (PHAEOPHYCEAE)( AND CA2+)

Chemoorientation in male gametes of Ectocarpus siliculosus in response to sexual pheromones is effected by two distinct mechanisms, chemokin esis and chemoklinotaxis. These are characterized by a strongly asymme tric bending pattern of the anteriorly-directed flagellum and transien t; unilateral bending of the hind flagellum, respectively. Removal of extracellular Ca2+ showed that normal flagellar movement and chemokine sis require millimolar concentrations of Ca2+ in the medium. The respo nse to pheromones is strongly inhibited by La3+, whereas the Ca2+-chan nel drugs, verapamil and nifedipine, have only little effect. Nifedipi ne nethertheless effectively inhibited accumulation at pheromone sourc es. These results are interpreted as an indication for the involvement of two pharmacologically distinct Ca2+-channels in chemokinesis and c hemoklinotaxis. The calmodulin-antagonist, trifluoperazine, induces, a t low concentrations, the same flagellar response in chemokinesis as t he pheromone, the mechanism of action remaining unknown.