P1-/P2-purinergic receptors on cultured rabbit retinal Müller cells

Adenosine 5'-triphosphate (ATP) and its metabolic products function as neurotransmitters or neuromodulators under the control of P1/P2-purinergic receptors. To determine the presence of these receptors on retinal Müller cells, spectrofluorometry was carried out on intracellular calcium mobilization, using Fura-2 images. Müller cells were cultured from adult rabbit retinas. Cytosolic calcium ([Ca2+]i) increased dose dependently with the application of ATP. This response was not blocked when a calcium channel blocker, nifedipine, was present, but this response was blocked, for the most part, when a P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) was present. Increase in [Ca2+]i was noted by the A1 or A2 agonist, which was blocked completely by each antagonist. Response to the A1 agonist was apparent only at high concentrations. Increase in [Ca2+]i was seen in some cells following administration of the P2x agonist, methylene ATP, only at a high concentration (100 microM) but not in the presence of PPADS (50 nM). The greatest increase in [Ca2+]i was induced by a P2y agonist, methyl thio ATP at 1 to 10 microM, which was completely blocked by PPADS. Cultured Müller cells are thus shown quite likely to possess the P1-/P2-purinergic receptors including A2 and P2y.