The hydra GSH receptor. Pharmacological and radioligand binding studies.

1. The GSH-induced feeding response of hydra has been studied using pharmacological and biochemical methods. 2. Dopaminergic agonists inhibit the response, whereas dopaminergic blocking agents increase it. Phosphodiesterase inhibitors completely inhibit the feeding response. 3. The specific binding of the competitive inhibitor of feeding response, [3H]glutamate, to hydra cellular fractions has been evaluated, and a strong GSH-sensitive binding has been observed in a nematocyst-rich fraction. 4. After pharmacological reduction of the nematocyst number, both feeding response and glutamate binding are severely reduced. 5. Ca2+ ions must be present for the feeding response to occur, whereas glutamate binding occurs both without Ca2+ and in the presence of EDTA.