Abstract
P 076
Glutamine induces acute osmotic swelling of retinal glial (Müller) cells – impact for hepatic retinopathy
Anett Karl1, Andreas Bringmann2, Andreas Reichenbach1
1Paul-Flechsig-Institut für Hirnforschung, Universität Leipzig, Leipzig; 2Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Leipzig, Leipzig
Objective
Chronic liver diseases may lead to hepatic retinopathy (HR) which is causally related to increased blood ammonium levels. Müller glial cells are capable to detoxify ammonium because of the glia-specific expression of glutamine synthetase (GS). GS produces glutamine from glutamate and ammonium which may result in elevated extracellular levels of glutamine during HR, where Müller cells display swollen cell nuclei. This may suggest a disturbance of Müller cell-mediated ion and water regulation, and may contribute to the development of retinal edema which further impairs retinal function. The aim of the study was to investigate i) whether an increase in extracellular glutamine induces a swelling of Müller cells, ii) whether a glutamine-induced swelling can be inhibited pharmacologically, and iii) whether glutamine causes a disturbance in the mitochondrial integrity of Müller cells.
Methods
Freshly isolated retinal slices and Müller cells of the rat were used to examine the size of Müller cell bodies. To mimic pathological alterations of the osmotic gradients in the retinal tissue, a hypotonic solution (60% of control osmolarity) was applied. The cationic dye JC-1 was used to record alterations of mitochondrial membrane potential.
Results
Administration of the hypotonic solution did not alter the size of Müller cell bodies. However, application of glutamine (5 mM) in hypotonic solution resulted in a swelling of Müller cell bodies. Glial cell swelling was significantly reduced by administration of inhibitors of oxidative/nitrosative stress and by substances which inhibit the transfer of glutamine into mitochondria and its conversion inside. JC-1-stained isolated Müller cells showed an elevated green/red ratio during perfusion with hypotonic solution containing glutamine (5 mM), suggesting a decrease in the mitochondrial membrane potential.
Conclusions
We conclude that glutamine plays a crucial role in the development of retinal edema and that increased glutamine levels as occurring in HR may induce the formation of oxidative/nitrosative stress mainly in the mitochondria of Müller cells. This may result in the formation of cytotoxic edema of Müller cells.
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