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A role for aquaporin-4 in fluid regulation in the inner retina

Published online by Cambridge University Press:  01 March 2009

MELINDA J. GOODYEAR ,
SHEILA G. CREWTHER  and
BARBARA M. JUNGHANS
MELINDA J. GOODYEAR
Affiliation:
School of Psychological Science, La Trobe University, Melbourne, Victoria, Australia
SHEILA G. CREWTHER*
Affiliation:
School of Psychological Science, La Trobe University, Melbourne, Victoria, Australia
BARBARA M. JUNGHANS
Affiliation:
School of Psychological Science, La Trobe University, Melbourne, Victoria, Australia School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
*
*Address correspondence and reprint requests to: Sheila G. Crewther, School of Psychological Science, La Trobe University, Melbourne, Victoria 3086, Australia. E-mail: s.crewther@latrobe.edu.au
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Abstract

Many diverse retinal disorders are characterized by retinal edema; yet, little experimental attention has been given to understanding the fundamental mechanisms underlying and contributing to these fluid-based disorders. Water transport in and out of cells is achieved by specialized membrane channels, with most rapid water transport regulated by transmembrane water channels known as aquaporins (AQPs). The predominant AQP in the mammalian retina is AQP4, which is expressed on the Müller glial cells. Müller cells have previously been shown to modulate neuronal activity by modifying the concentrations of ions, neurotransmitters, and other neuroactive substances within the extracellular space between the inner and the outer limiting membrane. In doing so, Müller cells maintain extracellular homeostasis, especially with regard to the spatial buffering of extracellular potassium (K+) via inward rectifying K+ channels (Kir channels). Recent studies of water transport and the spatial buffering of K+ through glial cells have highlighted the involvement of both AQP4 and Kir channels in regulating the extracellular environment in the brain and retina. As both glial functions are associated with neuronal activation, controversy exists in the literature as to whether the relationship is functionally dependent. It is argued in this review that as AQP4 channels are likely to be the conduit for facilitating fluid homeostasis in the inner retina during light activation, AQP4 channels are also likely to play a consequent role in the regulation of ocular volume and growth. Recent research has already shown that the level of AQP4 expression is associated with environmentally driven manipulations of light activity on the retina and the development of myopia.

Keywords

AQP4Kir4.1Müller cellsFluid homeostasisRetina
Type
Review
Information
Visual Neuroscience , Volume 26 , Issue 2 , March 2009 , pp. 159 - 165
Copyright
Copyright © Cambridge University Press 2009

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