ABSTRACT
Intense neuronal activity in the sensory retina is associated with a volume increase of neuronal cells (Uckermann et al., J. Neurosci. 2004, 24:10149) and a decrease in the osmolarity of the extracellular space fluid (Dmitriev et al., Vis. Neurosci. 1999, 16:1157). Here, we show the existence of an endogenous purinergic mechanism that prevents hypoosmotic swelling of retinal glial (Müller) cells in mice. In contrast to the cells from wild-type mice, hypoosmotic stress induced rapid swelling of glial cell somata in retinal slices from mice deficient in P2Y(1), adenosine A(1) receptors, or ecto-5'-nucleotidase (CD73). Consistently, glial cell bodies in retinal slices from wild-type mice displayed osmotic swelling when P2Y(1) or A(1) receptors, or CD73, were pharmacologically blocked. Exogenous ATP, UTP, and UDP inhibited glial swelling in retinal slices, while the swelling of isolated glial cells was prevented by ATP but not by UTP or UDP, suggesting that uracil nucleotides indirectly regulate the glial cell volume via activation of neuronal P2Y(4/6) and neuron-to-glia signaling. It is suggested that autocrine/paracrine activation of purinergic receptors and enzymes is crucially involved in the regulation of the glial cell volume.
Subject(s)
Cell Size , Neuroglia/cytology , Osmosis , Receptors, Purinergic/metabolism , Retina/cytology , Signal Transduction/physiology , 5'-Nucleotidase/deficiency , Adenine/analogs & derivatives , Adenine/pharmacology , Adenosine Diphosphate/analogs & derivatives , Adenosine Diphosphate/pharmacology , Animals , Barium Compounds/metabolism , Calcium/metabolism , Chlorides/metabolism , Cyclic AMP/metabolism , Drug Combinations , Enzyme Inhibitors/pharmacology , In Vitro Techniques , Inositol 1,4,5-Trisphosphate Receptors/deficiency , Mice , Mice, Knockout , Neuroglia/drug effects , Neurons/drug effects , Neurons/metabolism , Osmolar Concentration , Potassium Channel Blockers/pharmacology , Purinergic Agonists , Purinergic Antagonists , Pyrimidine Nucleotides/pharmacology , Quaternary Ammonium Compounds/pharmacology , Receptors, Purinergic/deficiency , Signal Transduction/drug effects , Signal Transduction/genetics , Thionucleotides/pharmacology , Time Factors , Valerates/pharmacology , Xanthines/pharmacologyABSTRACT
PURPOSE: Osmotic swelling of Müller glial cells has been suggested to contribute to retinal edema. We determined the role of adenosine signaling in the inhibition of Müller cell swelling in the murine retina. METHODS: The size of Müller cell somata was recorded before and during perfusion of retinal sections and isolated Müller cells with a hypoosmolar solution. Retinal tissues were freshly isolated from wild-type mice and mice deficient in A(1) adenosine receptors (A(1)AR(-/-)), or cultured as whole-mounts for three days. The potassium conductance of Müller cells was recorded in isolated cells, and retinal slices were immunostained against Kir4.1. RESULTS: Hypotonic exposure for 4 min induced a swelling of Müller cell bodies in retinal slices from A(1)AR(-/-) mice but not wild-type mice. Pharmacological inhibition of A(1) receptors or of the ecto-5'-nucleotidase induced hypoosmotic swelling of Müller cells from wild-type mice. Exogenous adenosine prevented the swelling of Müller cells from wild-type but not A(1)AR(-/-) mice. The antiinflammatory corticosteroid, triamcinolone acetonide, inhibited the swelling of Müller cells from wild-type mice; this effect was blocked by an antagonist of A(1) receptors. The potassium conductance of Müller cells and the Kir4.1 immunolabeling of retinal slices were not different between A(1)AR(-/-) and wild-type mice, both in freshly isolated tissues and retinal organ cultures. CONCLUSIONS: The data suggest that autocrine activation of A(1) receptors by extracellularly generated adenosine mediates the volume homeostasis of Müller cells in the murine retina. The swelling-inhibitory effect of triamcinolone is mediated by enhancement of endogenous adenosine signaling.
Subject(s)
Neuroglia/metabolism , Osmosis , Receptors, Purinergic P1/metabolism , Retina/cytology , Adenosine/metabolism , Adenosine/pharmacology , Animals , Immunohistochemistry , Ion Channel Gating/drug effects , Mice , Models, Biological , Neuroglia/drug effects , Organ Culture Techniques , Osmosis/drug effects , Potassium Channels, Inwardly Rectifying/metabolism , Receptors, Purinergic P1/deficiency , Signal Transduction/drug effectsABSTRACT
Prevention of osmotic swelling of retinal glial (Müller) cells is required to avoid detrimental decreases in the extracellular space volume during intense neuronal activity. Here, we show that glial cells in slices of the wildtype mouse retina maintain the volume of their somata constant up to approximately 4 min of perfusion with a hypoosmolar solution. However, calcium chelation with BAPTA/AM induced a rapid swelling of glial cell bodies. In glial cells of retinas from inositol-1,4,5-trisphosphate-receptor type 2-deficient (IP(3)R2(-/-)) mice, hypotonic conditions caused swelling of the cell bodies without delay. Exogenous ATP (acting at P2Y(1) receptors) prevented the swelling of glial cells in retinal slices from wildtype but not from IP(3)R2(-/-) mice. Müller cells from IP(3)R2(-/-) mice displayed a strongly reduced amplitude of the ATP-evoked calcium responses as compared to cells from wildtype mice. It is concluded that endogenous calcium signaling mediated by IP(3)R2 is required for the osmotic volume regulation of retinal glial cells.
