Characteristics of high-affinity [3H]adenosine binding to rat brain synaptosomes and turkey erythrocyte membranes.

High affinity binding sites for [3H]adenosine in rat brain and in turkey erythrocytes can be identified by binding experiments. Displacement experiments using a number of adenosine analogs indicate that these high affinity sites do not represent the R-type adenosine receptors which mediate activation of adenylate cyclase, although the binding is theophylline sensitive. Similarly, the binding of [3H]adenosine is not to the P-site, which mediates inhibition of adenylate cyclase, since the high affinity binding persists in the presence of 2',5'-dideoxyadenosine. Furthermore, these results remain qualitatively similar also in the presence of dipyridamole which blocks adenosine transport sites. We conclude that theophylline sensitivity does not indicate that [3H]adenosine binding sites correspond to adenosine receptors coupled to adenylate cyclase.