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  • Publication
    Metabotropic Receptor-Activated Calcium Increases and Store-Operated Calcium Influx in Mouse Müller Cells
    (Association for Research in Vision and Opthalmology, 2008-07) ; ; ;
    Purpose: Metabotropic receptor agonists that signal through Gq-coupled pathways increase Ca2+ in mammalian Müller cells by release from intracellular stores and Ca2+ influx pathways that have not been well described. The authors examined the involvement of voltage-dependent and non–voltage-dependent Ca2+ channels in metabotropic muscarinic receptor-activated Ca2+ increases and store-operated Ca2+ influx in cultured mouse Müller cells. Methods: Intracellular Ca2+ was measured using fluorescence imaging with the ratiometric dye fura-2. Currents were recorded using the whole-cell patch-clamp recording method. mRNA and protein were identified using reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemical approaches. Results: The muscarinic receptor agonist carbachol (3–20 μM) produced increases in Ca2+ that were blocked by the muscarinic receptor antagonists atropine and pirenzepine. RT-PCR confirmed mRNA for metabotropic M1 muscarinic receptors. Depletion of Ca2+ stores by the sarcoplasmic/endoplasmic Ca2+ ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid or the inhibition of phospholipase C occluded the carbachol-activated increase in Ca2+. Carbachol-activated Ca2+ increases in Müller cells were enhanced by the diacylglycerol derivative 1-oleyl-2-acetyl-sn-glycerol and were blocked by transient receptor potential (TRP) channel blockers Gd3+, La3+, 2-APB, and flufenamic acid. Both muscarinic receptor activation and thapsigargin treatment depleted Ca2+ stores and produced Ca2+ entry that was attenuated by La3+, 2-APB, Gd3+, and flufenamic acid. mRNA and protein for TRPC1 and TRPC6 were present in mouse Müller cells, and carbachol activated a Gd3+-sensitive, TRP-like cation channel. Conclusions: Metabotropic muscarinic receptor-activated Ca2+ increases in mouse Müller cells require the release of Ca2+ from intracellular stores and the activation of Ca2+ entry that involves TRP-like cation channels but is independent of voltage-dependent Ca2+ channels.
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