Abstract
Astrocytes exhibit a form of excitability based on variations of intracellular Ca(2+) concentration in response to various stimuli, including ADP, ATP, UTP and dinucleotides. Here, we investigate the presence of the recently cloned ADP-sensitive receptors, P2Y(12) and P2Y(13) subtypes, which are negatively coupled to adenylate cyclase, in cerebellar astrocytes. We checked the effect of specific agonists, 2-methylthioadenosine diphosphate (2MeSADP) and ADP, on adenylate cyclase stimulation induced by isoproterenol. Both agonists significantly reduced the cAMP accumulation induced by isoproterenol. The inhibitory effect was concentration-dependent with IC(50) values of 46 +/- 13 and 23 +/- 14 nM for 2MeSADP and ADP, respectively. The experiments were carried out in the presence of MRS-2179, a specific antagonist of P2Y(1) receptor, to avoid any contribution of this receptor. Using fura-2 microfluorimetry we also proved that astrocytes responded to 2MeSADP stimulations with calcium responses in the absence and also in the presence of MRS-2179. Both effects, inhibition of adenylate cyclase and intracellular calcium mobilization, were not modified by 2MeSAMP, an antagonist of P2Y(12) receptor, suggesting that were mediated by P2Y(13)-like receptors.