Receptor binding properties of di (1,N6-ethenoadenosine) 5', 5'''-P1, P4-tetraphosphate and its modulatory effect on extracellular glutamate levels in rat striatum.

Our aim was to investigate the neuromodulatory role of diadenosine tetraphosphate (Ap(4)A). Ap(4)A-binding sites were detected in striatum and hippocampus membranes using [(35)S]-ADP beta S as radioligand and Ap(4)A and epsilon-(Ap(4)A), di-ethenoadenosine tetraphosphate, as displacers. Effects of epsilon-(Ap(4)A) on extracellular glutamate levels were studied using intracerebral perfusion. Both areas contain high-affinity binding sites for [(35)S]-ADP beta S with K(d) values in the low nM range. [(35)S]-ADP beta S binding was displaced by Ap(4)A and epsilon-(Ap(4)A). At 1 and 10 microM doses, epsilon-(Ap(4)A) markedly decreased glutamate levels in the striatum. The possibility of Ap(4)A acting as an endogenous modulator of excitatory neurotransmission is discussed.