Center for Brain Research, Medical University of Vienna, Spitalgasse 4, A-1090 Vienna, Austria.
Philos Trans R Soc Lond B Biol Sci. 2011 Apr 27;366(1568):1265-77. doi: 10.1098/rstb.2010.0299.
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 In this review, we integrate the published data with the previously unpublished ultrastructural, dye loading and magnetic resonance imaging results.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.
晶状体无血管，从房水和玻璃体中获取营养。然而，尚不清楚哪些机制介导了这些房水和晶状体纤维细胞（FCs）之间溶质的转移。在这篇综述中，我们整合了已发表的数据和以前未发表的超微结构、染料加载和磁共振成像结果。出现的情况是，房水和纤维质之间溶质的转移是由四个过程决定的：（i）上皮细胞和 FCs 之间的细胞间隙中，由于钠（Na+）漏导，离子、水和小分子的旁分泌转运；（ii）特定载体和转运蛋白将这些溶质从细胞间隙转运到纤维细胞质中；（iii）缝隙连接偶联介导浅层和深层纤维之间的溶质通量、赤道区 Na(+)/K(+)-ATPase 驱动废物的外流以及纤维的电偶联；以及（iv）通过小窝和被覆小泡进行细胞间转运，以摄取大分子和胆固醇。有证据表明，溶质的 Na+驱动内流通过旁分泌和膜转运，而废物的 Na(+)/K(+)-ATPase 驱动外流则通过缝隙连接。这种微循环可能仅限于浅层皮质，在细胞器丢失区之外几乎不存在，在晶状体中形成溶质交换屏障。
