Purinergic Signalling (2012) 8 (Suppl 1):S61–S79 S65 Fig. 1 Expression of P2Y receptors in Müller cells of the adult rat and mouse retinal slices. Immunohistochemical staining was accomplished using anti-P2Y2 receptor (#APR-010) and anti-P2Y6 receptor (#APR- 011) antibodies. a No distinct immunoreactivity for the P2Y2 receptor (red) was observed in Müller cells. However, ganglion cells (asterisk) and structures within the inner plexiform layer (IPL), inner nuclear layer (INL), and outer plexiform layer (OPL) display faint staining. b P2Y4 receptor (red) is highly expressed in Müller cell end-feet (arrows), as detected using anti-P2Y4 receptor antibody (#APR-006). Additionally, a band of globular structures, probably representing synapse of bipolar cells in the ON-sublamina (ON) of the IPL, is stained for this receptor. c The staining pattern of the P2Y6 receptor (red) is similar to that of P2Y2. cells and that their differential subcellular expression patterns suggest they may regulate distinct processes in the lens under steady-state conditions. P2Y receptors in the heart, cardiovascular and vascular systems Purinergic signaling has been shown to be important in the cardiac and cardiovascular systems [17]. Presented are a number of studies examining the functions of these receptors in these vital systems. The insets in (b) and (c) show the ganglion cell layer (GCL) and the INL, respectively, at higher magnification. ONL outer nuclear layer, OFF OFF-sublamina of the IPL, PRS photoreceptor segments. Scale bars, 20 μm; inset scale bars, 10 μm. d Immunohistochemical staining was carried out using anti-P2Y4 receptor antibody. The slices were co-stained against the glial cell marker cellular retinaldehyde-binding protein (CRALBP); co-labeling yielded a yellow-orange merge signal. Arrows, Müller cell end-feet; arrowheads, Müller cell somata. GCL ganglion cell layer, IPL inner plexiform layer, NFL nerve fiber layer, ONL outer nuclear layer, PRS, photoreceptor segments. Scale bars, 20 μm. a–c Adapted from reference 12 with permission of John Wiley and Sons. d Adapted from reference 13 with permission of Wiley-Blackwell Cardiac fibroblasts are a major cell type in the heart. They have an important role in the functional and structural aspects of the organ by secreting growth factors, cytokines, and components of the extracellular matrix. During myo- cardial infarction, ATP and ADP are released [18]. In addition, various P2Y subtypes have been detected in rat cardiac fibroblasts [19], and various studies indicate that these receptors may play a role in cardiac function and may be involved in the pathological processes of cardiac diseases [20]. Cardiac fibroblasts are differentiated into myofibroblasts which seem to play an important role in myocardial infarction [21]. The differentiation of cardiac