The occurrence in and actions of amino acids on isolated supra oral sphincter preparations of the sea anemone Actinia equina.

1. L-glutamic acid reversibly inhibits the contractions of isolated circular muscle preparations from different body regions of the sea anemone Actinia equina to electrical stimulation.2. L-glutamic acid does not cause inhibition of contraction by conversion to ammonia or gamma-amino-butyric acid, but appears to act on a glutamate receptor.3. It is postulated that in Actinia equina there is a receptor for glutamic acid whose structural requirements for activation are met by comparatively few analogues of glutamic acid. Of thirty-four analogues tested, only seven were active, most were less active, and only homocysteic acid had a greater activity than L-glutamic acid.4. Glutamic acid does not depress conduction of contraction in circular muscle preparations.5. The inhibition produced by L-glutamic acid does not appear to be conducted from one part of a preparation to another.6. Glutamic acid occurs in high concentrations in supra oral sphincter preparations of Actinia equina.7. Glutamic acid is released into sea water from sphincter preparations at rest and the amount released is increased by electrical stimulation of the preparation. However, many other amino acids are released at rest and following electrical stimulation, so that it is difficult to suggest that glutamic acid may be involved as a neurotransmitter in the sea anemone.