Expression of pI(Cln) mRNA in cultured bovine lens epithelial cells: Response to changes in cell volume

Purpose. The authors recently established a link between swelling-activated myo-inositol efflux and chloride movement via anion channels in cultured bovine lens epithelial cells (BLECs). To further define this pathway, the relationship between cell volume, myo-inositol movement and mRNA expression of pI(Cln), a proposed chloride channel regulatory protein was investigated. Methods. To demonstrate the effect of cell volume changes on pI(Cln) transcription, BLECs were exposed to either hypertonic or hypotonic medium conditions. For rapid cellular shrinkage, BLECs were maintained at confluence in physiologic medium (257 ± 2 mosm) then transferred to sodium hypertonic medium (473 ± 6 mosm) or raffinose hypertonic medium (452 ± 2 mosm). For rapid cellular swelling, cells were switched from sodium hypertonic medium to physiologic medium ± tamoxifen. The expression of pI(Cln) mRNA was determined by Northern blot analysis. Results. Upon cell volume reduction (increasing intracellular osmolality), BLECs upregulate the expression of pI(Cln) mRNA. Contrastly, when cell volume rapidly increases (decreasing intracellular osmolality), BLECs moderately downregulate pI(Cln) mRNA, with expression levels reaching near physiologic control by 24 h. Blockage of swelling-activated chloride movement and osmolyte efflux with either tamoxifen or niflumic acid enhances the downregulation of pI(Cln) mRNA expression. Conclusions. In cultured BLECs, pI(Cln) transcriptional regulation appears to be responsive to cell volume fluctuations. These data suggest a converse relationship exists between pI(Cln) mRNA expression and changes in cell volume.