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

Chemoorientation in male gametes of Ectocarpus siliculosus in response to sexual pheromones is effected by two distinct mechanisms, chemokinesis and chemoklinotaxis. These are characterized by a strongly asymmetric bending pattern of the anteriorly-directed flagellum and transient; unilateral bending of the hind flagellum, respectively. Removal of extracellular Ca2+ showed that normal flagellar movement and chemokinesis require millimolar concentrations of Ca2+ in the medium. The response to pheromones is strongly inhibited by La3+, whereas the Ca2+-channel drugs, verapamil and nifedipine, have only little effect. Nifedipine nethertheless effectively inhibited accumulation at pheromone sources. These results are interpreted as an indication for the involvement of two pharmacologically distinct Ca2+-channels in chemokinesis and chemoklinotaxis. The calmodulin-antagonist, trifluoperazine, induces, at low concentrations, the same flagellar response in chemokinesis as the pheromone, the mechanism of action remaining unknown.