Müller cells express a variety of neurotransmitter receptors that permit them to "sense" the extracellular environment within the retina. We have used a battery of agonists and antagonists to characterize the purinergic receptor subtypes expressed on isolated tiger salamander Müller cells. Changes in intracellular calcium ion concentration ([Ca2+]i) in Müller cells were measured using the Ca2+ indicator dye Fura-2 and digital imaging microscopy. ATP, 2-methylthio-ATP, 2-methylthio-ADP, ADP, UTP, UDP, deoxyATP, and 3′-O-(4-benzoyl)benzoyl ATP evoked increases in [Ca2+]i in both the presence and absence of extracellular Ca2+. Therefore, the increases we observed were likely due to intracellular Ca2+ release mediated by G-protein-coupled P2Y receptor activation, rather than Ca2+ influx via P2X receptor channels. The P2Y1 receptor agonists 2-methylthio-ATP, 2-methylthio-ADP, and ADP evoked increases in [Ca2+]i that were inhibited by the P2Y1 receptor antagonists adenosine 3′-phosphate 5′-phosphosulfate and 2′-deoxy-N6-methyleneadenosine-3′,5′- bisphosphate. Responses to ADP were not completely inhibited by the P2Y1 receptor antagonists. The residual response to ADP could be mediated by P2Y13 receptors. UTP evoked an increase in [Ca2+]i that was partially inhibited by suramin, suggesting that Müller cells express P2Y2 and P2Y4 receptors. The P2Y6 receptor agonist UDP, and the P2Y11 receptor agonists deoxyATP, and 3′-O-(4-benzoyl)benzoyl ATP, evoked increases in [Ca2+]i in Müller cells. We conclude that isolated tiger salamander Müller cells express P2Y1, P2Y2, P2Y6, P2Y11, and possibly P2Y4 and P2Y13 receptors. Therefore, the physiological release of ATP, ADP, UTP, and UDP and/or their accumulation in the retina under pathological conditions could stimulate increases in [Ca2+]i in Müller cells.