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Muller cells express a variety of neurotransmitter receptors that permit them to sensethe 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 Muller cells. Changes in intracellular calcium ion concentration ([Ca 2+ ] i ) in Muller cells were measured using the Ca 2+ 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 [Ca 2+ ] i in both the presence and absence of extracellular Ca 2+ Therefore, the increases we observed were likely due to intracellular Ca 2+ release mediated by G-protein-coupled P2Y receptor activation, rather than Ca 2+ influx via P2X receptor channels. The P2Y 1 receptor agonists 2-methylthio-ATP, 2-methylthio-ADP, and ADP evoked increases in [Ca 2+ ] i that were inhibited by the P2Y 1 receptor antagonists adenosine 3'-phosphate 5'-phosphosulfate and 2'-deoxy-N6-methyleneadenosine-3',5'-bisphosphate. Responses to ADP were not completely inhibited by the P2Y 1 receptor antagonists. The residual response to ADP could be mediated by P2Y 13 receptors. UTP evoked an increase in [Ca 2+ ] i that was partially inhibited by suramin, suggesting that Muller cells express P2Y 2 and P2Y 4 receptors. The P2Y 6 receptor agonist UDP, and the P2Y 11 receptor agonists deoxyATP, and 3'-O-(4-benzoyl)benzoyl ATP, evoked increases in [Ca 2+ ] i in Muller cells. We conclude that isolated tiger salamander Muller cells express P2Y 1 , P2Y 2 , P2Y 6 , P2Y 11 , and possibly P2Y 4 and P2Y 13 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 [Ca 2+ ] i in Muller cells. GLIA 42:149-159, 2003. |
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