Developmental expression of metabotropic P2Y1 and P2Y2 receptors in freshly isolated astrocytes from rat hippocampus

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Abstract
There are at least three subtypes of cloned metabotropic P2 receptors linked to intracellular Ca2+ rises in rat brain cells, namely, P2Y1, P2Y2 and P2Y4. In this study we explore the subtypes of the metabotropic P2 receptors seen in freshly isolated astrocytes (FIAs) from P8‐P25 rats. We found by single cell RT‐PCR that in process‐bearing FIAs from hippocampi of P8‐P12 rats, 31% of the glial fibrillary acidic protein (GFAP) mRNA (+) cells expressed P2Y1 mRNA while only 5% of the cells tested expressed P2Y2 mRNA. The expression of P2Y1 receptor mRNA was not changed in FIAs from the hippocampi of P18‐P25 rats, but 38% of the GFAP mRNA (+) cells in the P18‐P25 age group then showed P2Y2 mRNA. We also studied whether the mRNA was expressing functional receptor protein by measuring Ca2+ responses to specific agonists for P2Y1 and P2Y2. We found that similar proportions of GFAP mRNA (+) FIAs responded to ATP or UTP as showed mRNAs for P2Y 1 and P2Y2, respectively. Total tissue RNA from P9 and P24 rat hippocampus showed a 2.8‐fold increase in P2Y2 mRNA levels from P9 to P24 with a decrease in P2Y1 mRNA. Thus, this study shows a marked up‐regulation of mRNA for P2Y2 from 9 to 24 days in rat hippocampus, and some of this increase is likely due to the protoplasmic astrocytes which is being translated into functional receptor protein in these cells.