Glutamate Immunoreactivity in Non-neuronal Cells of the Sea Anemone Metridium senile

The distribution of glutamate in the tentacles and oral disk of the sea anemone Metridium senile was investigated by wholemount immunohistochemistry with the use of a monoclonal antibody raised against the derivatization product {gamma}-L-glutamyl-L-glutamic acid. Immunoreactivity was localized in one class of tentacle nematocysts and on their associated threads. These nematocysts were concentrated at the distal end of tentacles, none being found at the base of tentacles or in the oral disk. Muscle end-feet of epitheliomuscular cells also stained in the longitudinal muscle of tentacle ectoderm. In contrast, immunostaining in the oral disk was confined to ectodermal granule-containing cells overlying the radial muscle. These results support a role for glutamate as an osmolyte precursor in nematocysts but provide little clue as to the functional significance of this amino acid in muscle and gland cells.