Modulation of A1 adenosine receptor function in rat brain by the polyamine, spermine.

Studies on factors modulating the binding of agonist ligands to A1 adenosine receptors in rat forebrain membranes revealed that the reduction of [3H]cyclohexyladenosine [( 3H]CHA) binding, observed after removing Mg2+ by pretreatment with ethylene-dinitrilo-tetraacetic acid (EDTA), was restored by the polyamine, spermine (1mM). Parallel electrophysiological experiments performed on rat hippocampal slices in Mg(2+)-free medium indicated that spermine also led to a recovery of the depressive effect of 1 microM adenosine on stimulus train-evoked neuronal Ca2+ influx. These observations suggest that the polyamine, spermine is, like Mg2+, able to control the physiological adenosine-mediated modulation of synaptic transmission by changing the affinity state of A1 receptors.