ADENOSINE A(2B)-RECEPTOR-MEDIATED CYCLIC-AMP ACCUMULATION IN PRIMARY RAT ASTROCYTES

1 The effects of adenosine receptor agonists and antagonists on the accumulation of cyclic AMP have been investigated in primary cultures of rat astrocytes. 2 Adenosine A(2)-receptor stimulation caused a concentration-dependent increase in the accumulation of [H-3]-cyclic AMP in cells prelabelled with [H-3]-adenine. The rank order of agonist potencies was 5'-N-ethylcarboxamidoadenosine (NECA; EC(50) = 1 mu M)) adenosine (EC(50) = 5 mu M))>2-chloroadenosine (ECS, = 20 mu M)>>CGS 21680 (EC(50)>10 mu M). The presence of 0.5 mu M dipyridamole, an adenosine uptake blocker, had no effect on the potency of adenosine. 3 The response to 10 mu M NECA was antagonized in a concentration-dependent manner by the non-selective adenosine receptor antagonists, xanthine amine congener (apparent K-D = 12 nM), PD 115,199 (apparent K-D = 134 nM) and 8-phenyltheophylline (apparent K-D = 126 nM). However, the A(1)-receptor-selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine, had no significant effect on the responses to NECA or 2-chloroadenosine at concentrations up to 1 mu M. 4 Stimulation of A(1)-receptors with the selective agonist, N-6-cyclopentyladenosine, did not alter the basal accumulation of [H-3]-cyclic AMP but inhibited a forskolin-mediated elevation of [H-3]-cyclic AMP accumulation by a maximal value of 42%. This inhibition was fully reversed in the presence of 0.1 mu M, 8-cyclopentyl-1,3-dipropylxanthine. 5 The time course for NECA-mediated [H-3]-cyclic AMP accumulation was investigated. The results suggest that there is a substantial efflux of cyclic AMP from the cells in addition to the rapid and sustained elevation of intracellular cyclic AMP (5 fold over basal) which was also observed. 6 These data indicate that rat astrocytes in primary culture express an A(2B)-adenosine receptor coupled positively to adenylyl cyclase. Furthermore, the presence of A(1)-receptors negatively coupled to adenylyl cyclase appears to have no significant effect on the A(2B)-receptor-mediated cyclic AMP responses to NECA and 2-chloroadenosine.