E.M. for at least 3 or 4 experiments performed in duplicate or triplicate. A P < 0.05 was taken as significant. Although strong previous evidences suggest that the pigmented epithelium and retinal neurons are a main source of ATP in the developing chick retina (Pearson et al., 2005 and Santos et al., 1999), Müller glial cells were shown to release ATP

during the propagation of calcium waves induced by mechanical stimulation in the adult rat retina (Newman, 2001). In order to verify if Müller glial cells from the developing chick retina could release ATP, we first investigated whether these cells presented ATP-filled vesicles that could be labeled ATM Kinase Inhibitor ic50 by quinacrine as described in rat astrocytes (Coco et al., 2003). This acridine derivative is a weak-base that binds ATP with high affinity and is widely used to visualize ATP-containing sub-cellular compartments in living cells (Bodin and Burnstock,

2001b and Irvin and Irvin, 1954). Enriched Müller glia cell cultures were incubated with 5 μM quinacrine for 5 min, washed and immediately visualized under fluorescence illumination (Fig. 1A). An abundant punctate fluorescent staining, distributed over cell cytoplasm, was observed. Neurotransmitter uptake into secretory vesicles requires an electrochemical proton gradient that is maintained by a v-ATPase (Montana et al., 2006). In order to verify if fluorescent puncta were secretory vesicles or other acidic organelles, enriched glial cultures were incubated with the v-ATPase inhibitor bafilomycin A1 (1 μM) for 1 h, prior to quinacrine staining. As shown in Fig. 1C, this procedure completely Kinase Inhibitor Library cell assay blocked the appearance of fluorescent granules within cultured cells. Recently, Sawada et al. (2008) identified a novel member of the SLC17 family of anion transporters (VNUT) that could actively accumulate nucleotides into liposomes. The uptake of ATP by VNUT was dependent on membrane potential and could be greatly inhibited by DIDS and Evans blue, two potent blockers

of the glutamate transporter VGLUT. Since quinacrine staining of Müller glia in culture was blocked by the v-ATPase inhibitor bafilomycin A1, the effect of Evans blue Endonuclease on quinacrine staining of cultured Müller cells was investigated (Fig. 2). Enriched glial cultures were incubated with 2 μM Evans blue for 1 h prior to quinacrine staining. In contrast to control cultures where fluorescent granules could be easily noticed (Fig. 2A), no quinacrine fluorescence was detected in cultures pre-treated with Evans blue (Fig. 2C). Moreover, quinacrine labeling over glial cells was restored when quinacrine negative, Evans blue-treated cultures were washed briefly and re-incubated in complete culture medium for 2 h, at 37 °C. When these cultures were stained again with quinacrine, an abundant punctuate fluorescent labeling over the cytoplasm of cells was observed (Fig. 2E).