Effect of maitotoxin on sea urchin egg fertilization and on Ca2+ permeabilities of eggs and intracellular stores

Abstract Maitotoxin (MTX), a potent marine toxin involved in ciguatera poisoning, inhibited sea urchin egg fertilization in a dose-dependent manner with an IC 50 of 7.5 × 10 −3 MU (mouse-unit)/ml. It did not affect male gametes fertilizing capabilities but provoked exocytosis in female gametes. It induced a K + loss simultaneously with a Na + entry into unfertilized eggs and increased the Ca 2+ influx at higher concentrations. On isolated cortex preparations, high concentrations of MTX reduced the rate of ATP-dependent ca 2+ accumulation into reticulum compartments and caused a leakage of Ca 2+ from a preparation pre-loaded with 45 Ca 2+ . Verapamil (10 −4 M) similarly blocked the increase of egg permeability to Ca 2+ and the effect on Ca 2+ sequesting into intracellular compartment, induced by MTX. Ion transport perturbations which evolved relatively slowly are probably not the direct cause of fertilization inhibition which could be related to a modification of the plasma membrane of the female gametes by this hydrophilic toxin.