Differences between rat primary cortical neurons and astrocytes in purine release evoked by ischemic conditions

In the brain, the levels of adenosine increase up to 100-fold during cerebral ischernia; however, the roles of specific cell types, enzymatic pathways and membrane transport processes in regulating intra- and extracellular concentrations of adenosine are poorly characterized. Rat primary cortical neurons and astrocytes were incubated with [³H]adenine for 30 min to radiolabel intracellular ATP. Cells were then treated with buffer, glucose deprivation (GD), oxygen-glucose deprivation (OGD), 100 μM sodium cyanide (NaCN) or 500 μM iodoacetate (IAA) for 1 h to stimulate the metabolism of ATP and cellular release of [³H]purines. The nucleoside transport inhibitor dipyridamole (DPR) (10 μM), the adenosine kinase inhibitor iodotubercidin (ITU) (1 μM), the adenosine deaminase inhibitor EHNA (1 μM) and the purine nucleoside phosphorylase inhibitor BCX-34 (10 μM) were tested to investigate the contribution of specific enzymes and transporters in the metabolism and release of purines from each cell type. Our results indicate that (a) under basal conditions astrocytes released significantly more [³H]adenine nucleotides and [³H]adenosine than neurons, (b) OGD, NaCN and IAA conditions produced significant increases in [³H]adenosine release from neurons but not astrocytes, and (c) DPR blocked [³H]inosine release from both astrocytes and neurons but only blocked [³H]adenosine release from neurons. These data suggest that, in these experimental conditions, adenosine was formed by an intracellular pathway in neurons and then released via a nucleoside transporter. In contrast, adenine nucleotide release and extracellular metabolism to adenosine appeared to predominate in astrocytes.