Abstract
P 074
Deletion of aquaporin-4 induces osmotic swelling in retinal Müller cells
Thomas Pannicke1, Antje Wurm1, Ianors Iandiev2, Gerald Seifert3, Christian Steinhäuser3, Peter Wiedemann2, Andreas Reichenbach1, Andreas Bringmann2
1Paul-Flechsig-Institut, Universität Leipzig, Leipzig, 2Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Leipzig, Leipzig, 3Institut für Zelluläre Neurowissenschaften, Universität Bonn, Bonn
Objective
Müller cells control the osmo- and ionhomeostasis of the retina mainly by transcellular K+ and water fluxes facilitated by Kir4.1 potassium and aquaporin-4 (AQP4) water channels. Kir4.1 and AQP4 proteins are colocalized in perivascular and vitreal membranes of Müller cells. We determined whether a deficiency in AQP4 is associated with alterations in the swelling properties of Müller cells and, thus, whether AQP4 is implicated in the homeostasis of the cellular volume under varying osmotic conditions.
Methods
The size of Müller cell bodies in retinal slices from control and AQP4-/- mice was recorded during superfusion with a hypoosmotic solution (60% of control osmolarity). Retinal slices were immunostained, and K+ currents were recorded from Müller cells.
Results
Application of a hypotonic solution caused a volume increase of Müller cell somata from AQP4-/- mice. Cells from wild-type animals did not swell under the same condition. Application of Ba2+ induced a swelling in both groups. The swelling of Müller cells from AQP4 /- mice could be reduced by several pharmacological agents: inhibitors of enzymes that produce inflammatory mediators, the reducing agent dithiothreitol, and by replacing extracellular Na+ ions. Moreover, activation of metabotropic glutamate, P2Y1 and adenosine A1 receptors inhibited Müller cell swelling via a complex signalling cascade. Deletion of AQP4 does not alter the retinal distribution of Kir4.1 and AQP1 immunoreactivities. Whole-cell recordings of isolated Müller cells displayed no significant differences in potassium currents between Müller cells from AQP4-/- and wildtype mice, confirming that lack of AQP4 does not modify the respective membrane properties of Müller cells.
Conclusions
The data suggest that glial cells in retinae of AQP4-/- animals are more sensitive to osmotic stress than glial cells in wildtype retinae. Müller cells of AQP4-/- animals are restricted in their ability to regulate their volume in response to alterations in the transmembrane osmotic gradient.
Seitenanfang