3H]kainic acid binding sites in chick cerebellar membranes

1. A total particulate fraction of chick cerebellar membranes, obtained by a simple method, has been found to specifically bind 3H]kainic acid. Non-neuronal tissue, like chick liver, does not show any appreciable specific binding under the same experimental conditions. 2. Specific 3H]kainic acid binding to chick cerebellar membranes increases linearly with tissue concentration, reaches the binding equilibrium almost instantaneously and is pH and temperature dependent. 3. Specifically bound 3H]kainic acid is displaced by suitable concentrations of unlabelled kainic acid, L-glutamic acid and other excitatory amino acid analogues, both agonist and antagonist. This pharmacological pattern agrees with the general pharmacological properties of kainic acid receptors. 4. Saturation kinetic studies of kainic acid binding sites show one single binding mode with an apparent dissociation constant KD = 278 nM and a maximum number of binding sites of 187 pmoles/mg of protein. 5. In view of the mentioned data and the high amount of receptor sites found in chick cerebellar membranes, as compared with related values in rat cerebellum, we suggest that these receptors play a different physiological role or that they have a different cellular localization in chick and rat cerebellum.