Osmoregulatory alterations in myo-inositol uptake by bovine lens epithelial cells. III. Effects of cycloheximide and colchicine on Na(+)-myo-inositol cotransporter activity under hypertonic conditions, inhibition of a plasma membrane osmotic stress protein.
Cultured bovine lens epithelial cells adapt to hypertonic sodium stress via an increase in Na(+)-myo-inositol cotransporter activity and accumulate myo-inositol. At least 12 hr of hypertonic exposure was necessary to enhance myo-inositol accumulation; and thereafter, uptake activity continued to increase throughout the duration of a 72-hr exposure period. Switching from hypertonic to isotonic medium for 24 hr reversed the otherwise elevated accumulation activity. The protein synthesis inhibitor, cycloheximide, did not affect myo-inositol uptake in isotonic medium but markedly decreased myo-inositol uptake in hypertonic medium. Cells exposed to hypertonic conditions and the microtubule disrupter, colchicine, similarly showed marked impairment of the otherwise enhanced myo-inositol uptake. These studies indicated that hypertonicity-induced elevation of Na(+)-myo-inositol cotransporter activity in cultured bovine lens epithelial cells is not solely attributed to the increased sodium gradient alone, but rather involves increased de novo synthesis of the Na(+)-myo-inositol cotransporter protein(s).
Department of Anatomy and Cell Biology, University of North Texas Health Science Center, Fort Worth/North Texas Eye Research Institut 76107.
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Cammarata
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Chen
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Zhou
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Reeves
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology*; D007294:Inositol / Q000493:pharmacokinetics*; D017136:Ion Transport; D007903:Lens Capsule, Crystalline / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis; D008870:Microtubules / Q000187:drug effects; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D012964:Sodium / Q000378:metabolism; D013997:Time Factors
D008565:Membrane Proteins; D007294:Inositol; D003513:Cycloheximide; D012964:Sodium; D003078:Colchicine