NIMODIPINE INHIBITS [H-3] NITROBENZYLTHIOINOSINE BINDING TO THE ADENOSINE TRANSPORTER IN HUMAN BRAIN

The inhibition of [H-3]nitrobenzylthioinosine ([H-3]NBI) binding to hu man parietal cortex membranes by adenosine transport inhibitors, adeno sine receptor agonists and antagonists and dihydropyridines was invest igated. While the adenosine transport inhibitors inhibited [H-3]NBI bi nding with K(i) values in the low nanomolar range and the adenosine A1 receptor agonist, cyclopentyladenosine, with a K(i) in the low microm olar range, no IC50 values could be obtained for the adenosine recepto r antagonists at concentrations up to 100,000 nM. Among the dihydropyr idines (+)-nimodipine was the most potent with a K(i) of 201 +/- 55 nM . Inhibition of adenosine transport thus may contribute to the clinica l effects of nimodipine in the central nervous system.