Key Words

In situ hybridisation to identify P2Y2 receptor mRNA was performed for the first time at the ultrastructural level on the thymus of adult male rats. These studies revealed transcripts for P2Y2 receptors in cortical T cells and endothelial cells of thymic blood vessels. These transcripts are likely to be linked with the production of functional P2Y2 receptors in these cells. In the T cells, transcripts for the P2Y2 receptor were localised in the cytoplasm as well as on the smooth endoplasmic reticulum and cell membrane. Dividing T cells also expressed P2Y2 receptor mRNA, mostly in the cytoplasm around chromosomal Abbreviations used in this paper DIG digoxigenin PBSphosphate-buffered saline SSC saline sodium citrate buffer material. Endothelial cells displaying labels for P2Y2 receptor transcripts were of cortical arteries/arterioles and capillaries and of postcapillary venules in the corticomedullary junction. P2Y2 mRNA transcripts were localised in the cytoplasm of endothelial cells, although they did not appear to be specifically associated with subcellular organelles or structures. In postcapillary venules, T cells displaying labelling for the P2Y2 receptor were seen migrating across the P2Y2 receptor mRNA-positive endothelium. Our findings are discussed in terms of the relationship between thymic immune cells and the endothelium. This includes the issue of immune cell trafficking into the circulation, and the ATP-related regulatory role and involvement of P2Y2 receptors in the rat thymus.