Investigative ophthalmology & visual science
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Invest. Ophthalmol. Vis. Sci. · Oct 2005
A developmental switch in the expression of aquaporin-4 and Kir4.1 from horizontal to Müller cells in mouse retina.
In adult retina, aquaporin-4 (AQP4) and inwardly rectifying K(+) (Kir4.1) channels localize to astrocyte and Müller cell membranes facing vascular and vitreous compartments, optimizing clearance of extracellular K(+) and water from the synaptic layers. However, it is unknown whether these channels are expressed at early developmental stages, before gliogenesis or angiogenesis take place in the neural retina. This study was conducted to determine the presence of AQP4 and Kir4.1 proteins in the developing mouse retina. ⋯ The findings showed that AQP4 and Kir4.1 protein expression is confined to differentiating horizontal cells before its expression in Müller cells. The finding of AQP4 in neurons is novel, since AQP4 expression within the central nervous system is restricted to glia. Also, the results demonstrated that AQP4 is a horizontal cell-specific immunomarker in neonatal retina. The transitory coexpression of AQP4 and Kir4.1 proteins by differentiating horizontal interneurons suggests that these cells mediate K(+) and water transcellular uptake until the initiation of phototransduction, when glial cells assume these functions.