Reeves R E, Cammarata P R
Department of Anatomy and Cell Biology, University of North Texas Health Science Center at Fort Worth, 76107, USA.
Invest Ophthalmol Vis Sci. 1996 Mar;37(4):619-29.
Cultured bovine lens epithelial cells (BLECs) exposed to sodium hypertonicity respond with an accumulation of intracellular myo-inositol. Using BLECs initially maintained at hypertonicity and reacting to a decrease in medium osmolality, a mechanism for the tonicity-activated release of myo-inositol was recognized. Alternatively, BLECs acclimated to sodium hypertonicity and subsequently transferred to high sodium osmolality plus hypergalactosemia rapidly accumulate intracellular galactitol, an experimental manipulation that permitted characterization of the role of sugar alcohols in polyol-activated myo-inositol efflux. The authors identify a communal transport route for tonicity-activated and polyol- activated myo-inositol release from cell to medium and demonstrate an association for myo-inositol efflux with chloride movement.
Two distinct experimental approaches were designed to delineate the physiological circumstances that initiate myo-inositol efflux. For tonicity-induced inositol efflux, BLECs were maintained at confluence in sodium hypertonic medium (473+/-6 mOsm) for 48 hours; afterward, the medium was replaced with isotonic medium (285+/-4 mOsm) containing 40 mM galactose +/- Sorbinil. For polyol-induced inositol release, hypertonically adapted BLECs were transferred to fresh sodium hypertonic medium containing 40 mM galactose (513+/- 10 mOsm).
On reduction in medium osmolality, intracellular myo-inositol was lost because of a rapid, transient efflux during the first 30 minutes, which was followed by a slow, sustained decrease in efflux during the next 12 hours. Inhibition of aldose reductase activity substantially diminished myo-inositol efflux from cell to galactose-containing, isotonic medium. Administration of phloretin significantly inhibited both tonicity-activated and polyol-activated myo-inositol release, as did the chloride channel blocker, niflumic acid.
In cultured bovine lens epithelial cells, tonicity-activated movement of myo-inositol from cell to medium and myo-inositol efflux as induced by intracellular polyol accumulation appear to be interactively associated with chloride movement and moderated by a common anionic (chloride) channel, carrier-mediated transport protein, or both.
暴露于高渗钠环境中的培养牛晶状体上皮细胞（BLECs）会出现细胞内肌醇积累的反应。利用最初维持在高渗环境并对培养基渗透压降低作出反应的BLECs，识别出了一种渗透压激活的肌醇释放机制。另外，适应高渗钠环境并随后转移至高钠渗透压加高半乳糖血症环境中的BLECs会迅速积累细胞内半乳糖醇，这种实验操作有助于确定糖醇在多元醇激活的肌醇外排中的作用。作者确定了从细胞到培养基的渗透压激活和多元醇激活的肌醇释放的共同转运途径，并证明了肌醇外排与氯离子移动有关。
设计了两种不同的实验方法来描述引发肌醇外排的生理情况。对于渗透压诱导的肌醇外排，将BLECs在高渗钠培养基（473±6 mOsm）中汇合培养48小时；之后，将培养基替换为含有40 mM半乳糖±索比尼尔的等渗培养基（285±4 mOsm）。对于多元醇诱导的肌醇释放，将适应高渗环境的BLECs转移至含有40 mM半乳糖（513±10 mOsm）的新鲜高渗钠培养基中。
培养基渗透压降低时，细胞内肌醇在前30分钟因快速、短暂的外排而减少，随后在接下来的12小时内外排缓慢、持续减少。醛糖还原酶活性的抑制显著减少了从细胞到含半乳糖的等渗培养基中的肌醇外排。根皮素的施用显著抑制了渗透压激活和多元醇激活的肌醇释放，氯离子通道阻滞剂尼氟酸也有同样的效果。
在培养的牛晶状体上皮细胞中，渗透压激活的肌醇从细胞到培养基的移动以及细胞内多元醇积累诱导的肌醇外排似乎与氯离子移动相互关联，并由共同的阴离子（氯离子）通道、载体介导的转运蛋白或两者共同调节。
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