Adenosine modulation of D-[H-3]aspartate release in cultured retina cells exposed to oxidative stress

In this study we evaluated the role of adenosine receptor activation on the K (+)-evoked D-[H-3]aspartate release in cultured chick retina cells expos ed to oxidant conditions. Oxidative stress, induced by ascorbate (3.5 mM)/F e2 + (100 mu M), increased by about fourfold the release of D-[3H]aspartate , evoked by KCI 35 mM in the presence and in the absence of Ca2 +. Tar agon ist of A(1) adenosine receptors, N-6-cyclopentyladenosine (CPA; 10 nM), inh ibited the K (+)-evoked D-[H-3]aspartate release in control in oxidized cel ls. The antagonist of A(1) adenosine receptor, 1,3-dipropyl-8-cyclopentylxa nthine (DPCPX; 50 nM), potentiated the release of D-[H-3]aspartate in oxidi zed cells, and reverted the effect observed in the presence of CPA 10 nM. H owever, in oxidized cells, when DPCPX was tested together with CPA 100 nM t he total release of D-[H-3]aspartate increased from 5.1 +/- 0.4% to 11.4 +/ - 1.0%, this increase being reverted by 3,7-dimethyl-1-propargylxanthine (D MPX; 100 nM), an antagonist of A(2A) adenosine receptors. In cells of both experimental conditions, the K (+) -evoked release of D-[H-3]aspartate was potentiated by the selective agonist of A(2A) adenosine receptors, 2-[4-(2- carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680; 10 nM), whereas the antagonist of these receptors, DMPX (100 nM), inhibited th e release of D-[H-3]aspartate in oxidized cells, but not in control cells. Adenosine deaminase (ADA; 1U/ml), which is able to remove adenosine from th e synaptic space, reduced the K (+) -evoked D-[H-3]aspartate release, from 5.1 +/- 0.4% to 3.1 +/- 0.3% in oxidized cells, and had no significant effe ct in control cells. The extracellular accumulation of endogenous adenosine , upon K (+) -depolarization, was higher in oxidized cells than in control cells, and was reduced by the inhibitors of adenosine transporter (NBTI) an d of ecto-5'-nucleotidase (AOPCP). This suggests that adenosine accumulatio n resulted from the outflow of adenosine mediated by the transporter, and f rom extracellular degradation of adenine nucleotide. Our data show that bot h inhibitory A(1) and excitatory A(2A) adenosine receptors are present in c ultured retina cells. and that the K (+) -evoked D-[H-3]aspartate release i s modulated by the balance between inhibitory and excitatory responses. Und er oxidative stress conditions, the extracellular accumulation of endogenou s adenosine seems to reach levels enough to potentiate the release of D-[H- 3]aspartate by the tonic activation of A(2A) adenosine receptors. (C) 2000 Elsevier Science Ltd. All rights reserved.