Homeostasis in the vertebrate lens: mechanisms of solute exchange

Author:

Dahm Ralf123,van Marle Jan4,Quinlan Roy A.5,Prescott Alan R.6,Vrensen Gijs F. J. M.7

Affiliation:

1. Center for Brain Research, Medical University of Vienna, Spitalgasse 4, A-1090 Vienna, Austria

2. Department of Biology, University of Padua, Via U. Bassi 58/B, I-35121 Padova, Italy

3. Institute of Molecular Biology gGmbH (IMB), Ackermannweg 4, 55128 Mainz, Germany

4. Department of Cell Biology and Histology, Academic Medical Center, Amsterdam, The Netherlands

5. School of Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, UK

6. Division of Cell Signalling and Immunology, College of Life Sciences, University of Dundee, Dundee DD1 4HN, UK

7. Department of Ophthalmology, Leiden University Medical Center, Leiden, The Netherlands

Abstract

The eye lens is avascular, deriving nutrients from the aqueous and vitreous humours. It is, however, unclear which mechanisms mediate the transfer of solutes between these humours and the lens' fibre cells (FCs). In this review, we integrate the published data with the previously unpublished ultrastructural, dye loading and magnetic resonance imaging results. The picture emerging is that solute transfer between the humours and the fibre mass is determined by four processes: (i) paracellular transport of ions, water and small molecules along the intercellular spaces between epithelial and FCs, driven by Na+-leak conductance; (ii) membrane transport of such solutes from the intercellular spaces into the fibre cytoplasm by specific carriers and transporters; (iii) gap-junctional coupling mediating solute flux between superficial and deeper fibres, Na+/K+-ATPase-driven efflux of waste products in the equator, and electrical coupling of fibres; and (iv) transcellular transfer via caveoli and coated vesicles for the uptake of macromolecules and cholesterol. There is evidence that the Na+-driven influx of solutes occurs via paracellular and membrane transport and the Na+/K+-ATPase-driven efflux of waste products via gap junctions. This micro-circulation is likely restricted to the superficial cortex and nearly absent beyond the zone of organelle loss, forming a solute exchange barrier in the lens.

Publisher

The Royal Society

Subject

General Agricultural and Biological Sciences,General Biochemistry, Genetics and Molecular Biology

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