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Keywords:

  • A1/D1 interactions;
  • adenosine;
  • dopamine release;
  • fast cyclic voltammetry

Abstract

Dopamine release is regulated by presynaptic dopamine receptors and interactions between adenosine and dopamine receptors have been well documented. In the present study, dopamine release from isolated striatal slices from Wistar rats was measured using fast cyclic voltammetry. Single-pulse stimulation (0.1 ms, 10 V) was applied every 5 min over a 2-h period. Superfusion with the adenosine (A)1 receptor agonist N6-cyclopentyladenosine (CPA), but not the A2 receptor agonist 3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl] phenyl]propanoic acid (CGS 21680), inhibited dopamine release in a concentration-dependent manner (IC50 3.80 × 10−7 m; n = 10). The dose–response curve to CPA was shifted to the right (IC50 6.57 × 10−6 m; n = 6, P < 0.05 vs. control) by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Neither the D1 agonist 6-chloro-APB nor the D1 antagonist R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3- benzazepine-7-ol (SCH 23390) altered dopamine release on their own. However, SCH 23390 (3 µm) significantly attenuated the response to CPA (IC50 1.44 × 10−5 m; n = 6, P < 0.01 vs. control). Furthermore, the inhibitory effect of CPA was significantly increased in the presence of 6-chloro-APB (1 µm). In radioligand binding experiments, CPA interacted with high- and low-affinity states of [3H]DPCPX-lableled A1 receptors. The high-affinity agonist binding to A1 receptors was inhibited by the stable guanosine triphosphate analogue Gpp(NH)p. In contrast, neither the proportion nor the affinity of high-affinity A1 receptors was altered by dopamine or SCH 23390. These results provide evidence that the inihibition of dopamine release by adenosine A1 receptors is dependent, at least in part, on the simultaneous activation of D1 dopamine receptors. While the mechanism underlying this interaction remains to be determined, it does not appear to involve an intramembrane interaction between A1 and D1 receptors.