Ultrastructural Identification of P2Y2 Receptor mRNA in the Rat Thymus

In situ hybridisation to identify P2Y(2) receptor mRNA was performed for the first time at the ultrastructural level on the thymus of adult male rats. These studies revealed transcripts for P2Y(2) receptors in cortical T cells and endothelial cells of thymic blood vessels. These transcripts are likely to be linked with the production of functional P2Y(2) receptors in these cells. In the T cells, transcripts for the P2Y(2 )receptor were localised in the cytoplasm as well as on the smooth endoplasmic reticulum and cell membrane. Dividing T cells also expressed P2Y(2 )receptor mRNA, mostly in the cytoplasm around chromosomal material. Endothelial cells displaying labels for P2Y(2 )receptor transcripts were of cortical arteries/arterioles and capillaries and of postcapillary venules in the corticomedullary junction. P2Y(2) 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 P2Y(2) receptor were seen migrating across the P2Y(2) 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 P2Y(2) receptors in the rat thymus.