Effect of euplotin C on swimming behavior in Paramecium

Abstract

The effect of euplotin C—a lipophilic toxic metabolite produced by the protist ciliate Euplotes crassus—on the swimming behavior was studied in a single‐celled system represented by the ciliate Paramecium primaurelia. When in P. primaurelia internal Ca2+ concentration coupled to membrane depolarization increases, a reversal in the direction of ciliary beating and consequently in swimming direction occurs. The ciliary reversal is correlated to Ca2+ influx amount. In this study, evidence was given that continuous ciliary reversal (CCR) duration, induced by high external KCl concentrations, is longer in euplotin C‐treated cells than in control cells. To test the hypothesis that euplotin C increases CCR duration by modulating a specific subtype of Ca2+ channel, selective Ca2+ channel blockers were used. Blocking L‐type channels by nimodipine and verapamil, N‐ and Q‐type channels by Ω‐conotoxins, fractions GVIA and MVIIC, significantly reduced the CCR duration evoked by membrane depolarization, suggesting an involvement of these channels in ciliary reversal in Paramecium. The effect of euplotin C on CCR duration persisted when Ω‐conotoxin GVIA or Ω‐conotoxin MVIIC were applied, conversely, it disappeared when L‐type channel blockers were used. The magnitude of the block by nimodipine and verapamil in the presence of euplotin C was comparable with that observed in the absence of euplotin C, suggesting that the Ca2+ channels modulated by euplotin C were dihydropyridine‐sensible calcium channels similar to L‐type channels found in mammalian cells.