ANTAGONISM OF GLUTAMATE RECEPTORS BY A CHROMATOGRAPHIC FRACTION FROM THE EXUDATE OF THE SEA-ANEMONE PHYLLACTIS-FLOSCULIFERA

In the search for new glutamate antagonists it seems promising to char acterize the effects of venom from invertebrates that prey mainly on c rustaceans. In this work, the exudate of the sea anemone Phyllactis fl osculifera was used as a source of this type of compound. The action o f chromatographic fraction D from P. flosculifera was tested upon micr oion-tophoretically evoked glutamate responses in intracellular record ings from central neurons of the land snail Zachrysia guanensis. Path application of fraction D (2-8 mg/ml, n = 13) diminished both the exci tatory and the inhibitory components of glutamate agonists in Z. guane nsis neurons; this action was dose-dependent and partially reversible, Fraction D actions were also tested in the multiunit spontaneous and mechanically evoked responses of the glutamatergic junction between ha ir cells and afferent neurons of the axolotl Ambystoma tigrinum. Press ure ejection of fraction D in concentrations ranging from 0.5 to 2 mg/ ml (n = 9) decreased the spontaneous and mechanically evoked activity of semicircular canal afferent neurons and the responses evoked by kai nic acid and lpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid. This action was also dose-dependent and partially reversible. These re sults indicate that fraction D acts as a glutamate receptor antagonist in snail and amphibian neurons, Further studies are required to chara cterize the active compounds responsible for this action and its speci ficity upon the subtypes of glutamate receptors. (C) 1996 Elsevier Sci ence Ltd.