Adenosine A 1 receptor-mediated inhibition of cyclic AMP accumulation in type-2 but not type-1 rat astrocytes

Abstract

The effects of adenosine receptor-selective ligands on [ 3H]cyclic AMP accumulation have been investigated in type-1 and type-2 astrocyte-enriched cultures derived from neonatal rat forebrains. In type-1 astrocytes, 5′- N-ethylcarboxamidoadenosine (NECA) caused a concentration-dependent increase in [ 3H]cyclic AMP accumulation (EC 50 = 1.2 μM) which was antagonised by pretreatment with either xanthine amine congener (8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl]oxy]-phenyl]-1,3-dipropylxanthine, apparent K d = 9 nM) or PD115,199 ( N-[2-(dimethylamino)ethyl]- N-methyl-4-(1,3-dipropylxanthine)benzene sulphonamide, apparent K d = 122 nM). In these cultures, N 6-cyclopentyladenosine (CPA), did not affect forskolin- or isoprenaline-mediated elevations of [ 3H]cyclic AMP accumulation. These data indicate that type-1 astrocytes possess adenosine A 2B but not adenosine A 1 receptors coupled to adenylyl cyclase. In type-2 astrocyte-enriched cultures, 10 μM NECA caused significant elevations of [ 3H]cyclic AMP accumulation which were similarly inhibited by either 1 μM xanthine amine congener or 10 μM PD115,199 suggesting that they were primarily due to adenosine A 2B receptor stimulation. However, CGS 21680 ((2-[[4-(2-carboxyethyl) phenethyl]-amino]adenosine-5′- N-ethylcarboxamide, 10 μM), also significantly increased [ 3H]cyclic AMP accumulation in type-2 astrocytes suggesting the additional presence of adenosine A 2A receptors. Forskolin-mediated elevations of [ 3H]cyclic AMP accumulation in type-2 astrocytes were inhibited in a concentration-dependent manner by CPA. This effect was reversed by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 μM), confirming the presence of adenosine A 1 receptors negatively coupled to adenylyl cyclase in type-2 astrocytes.