( 3H)dipyridamole and ( 3H)nitrobenzylthioinosine binding sites at the human parietal cortex and erythrocyte adenosine transporter: A comparison

We compared the binding sites of the adenosine transport inhibitors ( 3H)dipyridamole (DPR) and ( 3H)nitrobenzylthioinosine (NBI) in human parietal cortex and erythrocytes. In comparison with guinea pig ( 3H)DPR marked only slightly more binding sites than ( 3H)NBI with a Bmax of 1080±29 and 780±7 fmol/mg protein respectively in parietal cortex and 24288±2725 and 20875±1905 fmol/mg protein respectively in erythrocytes. NBI displaced ( 3H)DPR binding completely from its binding sites at about K D/2 concentrations in parietal cortex as well as erythrocytes with inhibition constants comparable to its dissociation constants. Lineweaver-Burke analysis in erythrocytes indicated a competitive inhibition of ( 3H)DPR binding by NBI. Pharmacological characterization of ( 3H)DPR binding sites in human erythrocytes is consistent with their localization on adenosine transporters. These findings provide evidence that as opposed to guinea pig ( 3H)DPR and ( 3H)NBI largely label binding sites to the same adenosine transporter in human erythrocytes and parietal cortex.