Abstract
Layers of rabbit corneal endothelial cells were cultured on permeable inserts. We characterized the diffusional permeability of the cell layer to nonelectrolyte and charged molecules and compared the diffusional and filtration permeabilities of the paracellular and transcellular pathways. We determined the rates of diffusion of 3H- and 14C-labeled nonelectrolyte test molecules and estimated the equivalent pore radius of the tight junction. Negatively charged molecules permeate slower than neutral molecules, while positively charged molecules permeate faster. Palmitoyl-dl-carnitine, which opens tight junctions, caused an increase of permeability and equivalent pore radius. Diffusional water permeability was determined with 3H-labeled water; the permeabilities of the tight junction and lateral intercellular space were calculated using tissue geometry and the Renkin equation. The diffusional permeability (P d ) of the paracellular pathway to water is 0.57 μm s−1 and that of the transcellular path is 2.52 μm s−1. From the P d data we calculated the filtration permeabilities (P f ) for the paracellular and transcellular pathways as 41.3 and 30.2 μm s−1, respectively. In conclusion, the movement of hydrophilic molecules through tight junctions corresponds to diffusion through negatively charged pores (r = 2.1 ± 0.35 nm). The paracellular water permeability represents 58% of the filtration permeability of the layer, which points to that route as the site of sizable water transport. In addition, we calculated for NaCl a reflection coefficient of 0.16 ≤ σNaCl ≤ 0.33, which militates against osmosis through the junctions and, hence, indirectly supports the electro-osmosis hypothesis.
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Acknowledgements
This work was supported by NIH grant EY06178 and by CONICET grant PIP 01688, both to J. F., who is a career investigator with the Argentine National Research Council (CONICET).
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Friedrich P. Diecke is now deceased.
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Diecke, F.P., Cacace, V.I., Montalbetti, N. et al. Comparative Permeabilities of the Paracellular and Transcellular Pathways of Corneal Endothelial Layers. J Membrane Biol 242, 41–51 (2011). https://doi.org/10.1007/s00232-011-9375-5
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DOI: https://doi.org/10.1007/s00232-011-9375-5