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R. T. Mathias, J. Gao, X. Sun, L. Moore, T. W. White, P. R. Brink; The Circulation of Sodium and Fluid Through Lens Gap Junctions. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3459.
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A fundamental question on the biophysical properties of gap junction channels concerns their role in transporting fluid through stratified epithelia. Surprisingly, no previous data address this question. We recently modeled fluid flow through gap junction channels of the ciliary body, and concluded the channels could indeed carry near isotonic fluid, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be small and difficult to measure, but in the lens, intracellular fluid flow from central fibers to the surface crosses hundreds of layers of gap junctions and should require a large hydrostatic gradient.
A microelectrode based pressure sensing system was constructed to measure intracellular hydrostatic pressure in the lens.
In wild type (WT) mouse lenses, the measured pressure gradient varied from an average of 330 mmHg at the center to zero at the surface. In Cx46 for Cx50 knock in (KI) lenses, mature fiber cell coupling conductance is 2.2-times higher than that of WT. Hydrostatic pressure in KI lenses varied from an average of 150 mmHg at the center to zero at the surface, or about 2.2-times lower than that in WT. In GPX knockout (KO) lenses, mature fiber cell gap junction coupling is 1.7-times lower than that of WT. Hydrostatic presure in KO lenses varied from an average of 490 mmHg at the center to 0 at the surface, or about 1.5-times higher than that in WT. When WT lenses were bathed in high potassium low sodium solution to block the normal circulation of sodium, the hydrostatic pressure went to zero over the same time period as the circulation of sodium went to zero.
These data suggest there is indeed a vigorous circulation of fluid through the lens,the intracellular leg of fluid circulation is through fiber cell gap junction channels, and the fluid flow is coupled to the lens circulation of sodium.
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