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J Fischbarg, JM Sanchez, A Rubashkin, P Iserovich, K Kuang, FP J Diecke; Time Course Of Current-induced Fluid Flow Across Corneal Endothelium . Invest. Ophthalmol. Vis. Sci. 2002;43(13):902.
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Purpose:. We have reported that application of electrical current induces fluid movements across corneal endothelium. We investigated the time course of this phenomenon to try to distinguish between two possible explanations, electro-osmosis, or local osmosis. Methods: We used de-epithelialized rabbit corneal endothelial preparations mounted in a volume clamp chamber endowed with current-sending electrodes. Fluid movements were detected with a nanoinjector at a resolution of ∼ 10 nL. The voltage output of the nanoinjector instrument went to both a chart recorder and to a 2-channel Dataq interface for a computer running the data-acquisition program Windaq. Current was recorded using the second channel. Data were collected every 0.2 seconds. We also did theoretical modeling; using the program FlexPDE, we modeled the local osmotic effect resulting from solute accumulation at the apical membrane induced by apical solute flux into an apical unstirred layer for a range of membrane osmotic permeabilities. Results: After mounting the endothelial preparations, we verified that the transendothelial rate of fluid transport reached a steady state level. At that point, we imposed a current step (total of 19 current steps in four different preparations). In all cases, fluid movement either increased or decreased, depending on the current polarity (+ current, from basolateral (stroma) to apical, induced an increase). Importantly, the change in fluid movement was detected as soon as the current was imposed. The delay was at most ∼3 seconds, and the characteristic rise time was 0.6 s. In contrast, the time course for the simulated local osmotic flow was much slower. Using an osmotic permeability (Pf) value of 93 µm/s for the endothelium, the rise time was 32 minutes. Even using the maximum theoretical Pf value of 600 µm/s (for an endothelium 4 µm in height and no membrane barrier), the rise time was ∼ 40 s. Conclusion: The time course of current-induced transendothelial fluid movement is consistent with electro-osmosis but not with our simulations of local osmosis. The relevance of these findings for the mechanism of spontaneous transendothelial fluid transport is being investigated. CR: N. Support: USPHS Grant EY06178, and RPB, Inc.
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