Interactions of the anticonvulsant carbamazepine with adenosine receptors. 1. Neurochemical studies.

At therapeutic concentrations the tricyclic anticonvulsant carbamazepine inhibited the binding of the adenosine analogue [3H]L-N6-phenylisopropyladenosine ([3H]PIA) to rat brain membranes (Ki = 46 microM) in vitro. Carbamazepine interacted much less potently with muscarinic cholinergic, beta-adrenergic, gamma-aminobutyric acid, or L-glutamate binding sites. Carbamazepine was of lower potency (Ki = 112 microM) as an inhibitor of the binding of the putative A2 adenosine agonist [3H]5'-N-ethylcarboxamidoadenosine. GTP greatly reduced the potencies of purine agonists, but not antagonists, as inhibitors of [3H]PIA. The potency of carbamazepine, like that of the antagonist theophylline, was not reduced by GTP. Studies on the adenosine-stimulated adenylate cyclase activity in guinea pig brain slices also revealed theophyllinelike activity of carbamazepine. The possible relevance of agonist and antagonist interactions with adenosine receptors to the anticonvulsant action of carbamazepine is discussed.