The presynaptic effect of fractions isolated from the sponge Tedania ignis.

Two fractions from the sponge Tedania ignis which have presynaptic effects were isolated. In neuromuscular junctions of Rana pipiens, the crude fraction decreases the amplitude of the evoked endplate potential and increases the frequency of miniature endplate potentials (MEPP), without effects on their amplitude or shape. Elution with 1 M acetic acid through Sephadex G15 produces three peaks, only one of which contains the biological activity. The compounds in this peak possess a molecular weight close to 900. Elution with 1M acetic acid through BioGel P2 produces 9 peaks, only 2 of which are biologically active. One of these fractions (f alpha) increases the frequency of MEPP and another fraction (f beta) inhibits the evoked release of neurotransmitter. None of the fractions change the amplitude or shape of MEPP, nor do they modify the resting membrane or action potentials in frog muscle. The action of f alpha occurs in low (15 microM) Ca2+, while the effect of f beta is antagonized by raising the extracellular Ca2+ concentration above 1.8 MM. Fraction beta antagonizes the increase of acetylcholine release produced by the venom of the black widow spider Latrodectus mactans mactans. This antagonistic action of f beta is reversible and the effect of the spider venom reappears if the sponge toxin is washed out with normal Ringer's solution.