title: Genetic deletion of laminin isoforms β2 and γ3 induces a reduction in Kir4.1 and aquaporin-4 expression and function in the retina.
abstract: BACKGROUND
  Glial cells such as retinal Müller glial cells are involved in potassium ion and water homeostasis of the neural tissue. In these cells, inwardly rectifying potassium (Kir) channels and aquaporin-4 water channels play an important role in the process of spatial potassium buffering and water drainage. Moreover, Kir4.1 channels are involved in the maintenance of the negative Müller cell membrane potential. The subcellular distribution of Kir4.1 and aquaporin-4 channels appears to be maintained by interactions with extracellular and intracellular molecules. Laminins in the extracellular matrix, dystroglycan in the membrane, and dystrophins in the cytomatrix form a complex mediating the polarized expression of Kir4.1 and aquaporin-4 in Müller cells.
  
  
  RESULTS
  The aim of the present study was to test the function of the β2 and γ3 containing laminins in murine Müller cells. We used knockout mice with genetic deletion of both β2 and γ3 laminin genes to assay the effects on Kir4.1 and aquaporin-4. We studied protein and mRNA expression by immunohistochemistry, Western Blot, and quantitative RT-PCR, respectively, and membrane currents of isolated cells by patch-clamp experiments. We found a down-regulation of mRNA and protein of Kir4.1 as well as of aquaporin-4 protein in laminin knockout mice. Moreover, Müller cells from laminin β2 and γ3 knockout mice had reduced Kir-mediated inward currents and their membrane potentials were more positive than those in age-matched wild-type mice.
  
  
  CONCLUSIONS
  These findings demonstrate a strong impact of laminin β2 and γ3 subunits on the expression and function of both aquaporin-4 and Kir4.1, two important membrane proteins in Müller cells.
authors.affiliation: Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany. petra.hirrlinger@medizin.uni-leipzig.de
authors.forename: Petra G
authors.initials: PG
authors.lastname: Hirrlinger
authors.forename: Thomas
authors.initials: T
authors.lastname: Pannicke
authors.forename: Ulrike
authors.initials: U
authors.lastname: Winkler
authors.forename: Thomas
authors.initials: T
authors.lastname: Claudepierre
authors.forename: Shweta
authors.initials: S
authors.lastname: Varshney
authors.forename: Christine
authors.initials: C
authors.lastname: Schulze
authors.forename: Andreas
authors.initials: A
authors.lastname: Reichenbach
authors.forename: William J
authors.initials: WJ
authors.lastname: Brunken
authors.forename: Johannes
authors.initials: J
authors.lastname: Hirrlinger
mesh_terms: D000818:Animals; D051401:Aquaporin 4 / Q000032:analysis / Q000235:genetics*; D015536:Down-Regulation; D017353:Gene Deletion; D007797:Laminin / Q000235:genetics* / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D018345:Mice, Knockout; D009457:Neuroglia / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D000098854:Kcnj10 Channel
chemical_list: C496031:Aqp4 protein, mouse; D051401:Aquaporin 4; D000098854:Kcnj10 Channel; C504220:Lamc3 protein, mouse; D007797:Laminin; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; C058783:laminin beta2