Markovich D, Verri T, Sorribas V, Forgo J, Biber J, Murer H
Institute of Physiology, University of Zürich, Switzerland.
Pflugers Arch. 1995 Aug;430(4):459-63. doi: 10.1007/BF00373881.
Renal proximal tubular Na-dependent phosphate transport (Na/Pi cotransport) has been studied extensively in the opossum kidney (OK) cell line. Recently, we cloned a complementary deoxyribonucleic acid (cDNA) (NaPi-4) from OK cells encoding an apical NaPi cotransport system. OK cells exposed to a low-Pi medium, as compared to high-Pi media, responded with an increase in Na/Pi cotransport, which was followed by an increase in NaPi-4 messenger ribonucleic acid (mRNA) abundance; maximal stimulation of Na/Pi cotransport was reached in 2 h, with no further increase for up to 16 h. NAPi-4 mRNA abundance was unaltered for 2 h, then increased to a maximum after 6-16 h in cells treated with low Pi medium. NaPi-4 mRNA decay rate was lowered by low-Pi media when compared to high-Pi media, with no increase in the NaPi-4 mRNA transcription rate. These data suggest that the upregulation of Na/Pi cotransport in OK cells by low-Pi media involves two regulatory mechanisms: an immediate (early) increase (after 2 h) in the expression of Na/Pi cotransport, independent of mRNA synthesis or stability, and a delayed (late) effect (after 4-6 h), resulting in an increase in NaPi-4 mRNA abundance, due to an increased stability.
在负鼠肾（OK）细胞系中，对肾近端小管钠依赖性磷酸盐转运（钠/磷酸盐共转运）进行了广泛研究。最近，我们从OK细胞中克隆了一种互补脱氧核糖核酸（cDNA）（NaPi - 4），其编码一种顶端钠/磷酸盐共转运系统。与高磷培养基相比，暴露于低磷培养基的OK细胞，其钠/磷酸盐共转运增加，随后NaPi - 4信使核糖核酸（mRNA）丰度增加；在2小时内达到钠/磷酸盐共转运的最大刺激，在长达16小时内没有进一步增加。在低磷培养基处理的细胞中，NaPi - 4 mRNA丰度在2小时内未改变，然后在6 - 16小时后增加到最大值。与高磷培养基相比，低磷培养基降低了NaPi - 4 mRNA的衰减率，而NaPi - 4 mRNA转录率没有增加。这些数据表明，低磷培养基对OK细胞中钠/磷酸盐共转运的上调涉及两种调节机制：一种是即时（早期）增加（2小时后）钠/磷酸盐共转运的表达，与mRNA合成或稳定性无关；另一种是延迟（晚期）效应（4 - 6小时后），由于稳定性增加导致NaPi - 4 mRNA丰度增加。
