Yamauchi A, Uchida S, Preston A S, Kwon H M, Handler J S
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Am J Physiol. 1993 Jan;264(1 Pt 2):F20-3. doi: 10.1152/ajprenal.1993.264.1.F20.
Myo-inositol is a major compatible osmolyte accumulated in the hypertonic renal medulla and in Madin-Darby canine kidney (MDCK) cells cultured in hypertonic media. Myo-inositol is taken up by MDCK cells on a Na(+)-coupled transporter whose activity increases sixfold 24 h after cells are switched to hypertonic medium. To investigate the mechanism of regulation of the cotransporter by hypertonicity, we used the cDNA encoding the canine Na(+)-myo-inositol cotransporter that we recently cloned to measure the abundance of the mRNA for the cotransporter and its rate of transcription after changes in osmolality. When MDCK cells were switched from isotonic to hypertonic medium, cotransporter mRNA abundance rose 10-fold in 16 h. Transcription of the cotransporter gene also rose and 16 h after the switch reached a peak approximately 15-fold that in isotonic cells. When cells were switched back to isotonic medium, mRNA abundance and transcription of the gene returned to isotonic levels in 8 h and transport rate reached isotonic levels in 48 h. Thus transcription appears to be the primary step in regulation of myo-inositol transport by hypertonicity.
肌醇是一种主要的相容性渗透溶质，在高渗的肾髓质以及在高渗培养基中培养的Madin-Darby犬肾（MDCK）细胞中积累。MDCK细胞通过一种与Na⁺偶联的转运体摄取肌醇，当细胞转换至高渗培养基后24小时，该转运体的活性增加6倍。为了研究高渗对该共转运体的调节机制，我们使用了最近克隆的编码犬Na⁺-肌醇共转运体的cDNA，来测量渗透压改变后共转运体mRNA的丰度及其转录速率。当MDCK细胞从等渗培养基转换至高渗培养基时，共转运体mRNA丰度在16小时内上升了10倍。共转运体基因的转录也增加，转换后16小时达到峰值，约为等渗细胞中的15倍。当细胞再转换回等渗培养基时，mRNA丰度和基因转录在8小时内恢复到等渗水平，转运速率在48小时内达到等渗水平。因此，转录似乎是高渗调节肌醇转运的主要步骤。
