Activation of adenosine A1 and A2A receptors modulates dopamine D2 receptor-induced responses in stably transfected human neuroblastoma cells

Adenosine can influence dopaminergic neurotransmission in the basal ganglia via postsynaptic interaction between adenosine A(2A) and dopamine D-2 receptors, We have used a human neuroblastoma cell line (SH-SY5Y) that was found to express constitutively moderate levels of adenosine A(1) and A(2A) receptors (similar to 100 fmol/mg of protein) to investigate the interactions of A(2A)/D-2 receptors, at a cellular level. After transfection with human D-2L receptor cDNA, SH-SY5Y cells expressed between 500 and 1,100 fmol of D-2 receptors/mg of protein. In membrane preparations, stimulation of adenosine A(2A) receptors decreased the affinity of dopamine D-2 receptors for dopamine. In intact cells, the calcium concentration elevation induced by KCI treatment was moderate, and dopamine had no effect on either resting intracellular free Ca2+ concentration ([Ca2+](i)) or KCl-induced responses. In contrast, pretreatment with adenosine deaminase for 2 days dramatically increased the elevation of [Ca2+](i) evoked by KCl, which then was totally reversed by dopamine. The effects induced by 48-h adenosine inactivation were mimicked by application of adenosine A(1) antagonists and could not be further reversed by acute activation of either A(1) or A(2A) receptors, Acute application of the selective A(1) receptor agonist CGS-21680 counteracted the D-2 receptor-induced [Ca2+](i) responses. The present study shows that SH-SY5Y cells are endowed with functional adenosine A(2A) and A(1) receptors and that A(2A) receptors exert an antagonistic acute effect on dopamine D-2 receptor-mediated functions. In contrast, A(1) receptors induce a tonic modulatory role on these dopamine functions.