Effect of ammonium on the expression of osmosensitive genes in Madin–Darby canine kidney cells

• Published in: The Journal of physiology 2005-03, Vol.563 (2), p.497
• Main Authors: Wolfgang Neuhofer, Monika Vastag, Maria-Luisa Fraek, Franz-X Beck
• Format: Article
• Language: English
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2004.077784

The cells of the kidney medulla are exposed routinely to high extracellular concentrations of various solutes including NaCl, urea and ammonium (NH 4 + ). Although it is well established that the expression of a variety of osmosensitive genes and proteins, which confer cytoprotection on renal medullary cells, is induced by high NaCl concentrations, the role of NH 4 + in these cellular responses is unclear. This study thus addressed the effect of NH 4 + on the expression of the betaine/GABA transporter (BGT-1), the sodium/ myo -inositol cotransporter (SMIT), aldose reductase (AR), and heat shock protein 70 (HSP70) in Madin–Darby canine kidney (MDCK) cells, using Northern and Western blot analyses and enzyme-linked immunosorbent assay (ELISA). The incidence of apoptosis was monitored by determining caspase-3 activity and annexin V binding. Addition of NH 4 Cl (50 m m ; total osmolality 400 mosmol (kg H 2 O) −1 to the medium was more effective than equiosmolar NaCl in increasing BGT-1 and HSP70 mRNA abundance, but less effective in enhancing BGT-1 and HSP70 expression at the protein level. Qualitatively similar results were obtained for SMIT and AR mRNAs. Exposure to both isotonic and hypertonic, NH 4 Cl-containing medium enhanced apoptosis compared with equiosmolar, NaCl-containing media. These results suggest that, in addition to NaCl, NH 4 Cl may play a role in regulating the intracellular accumulation of organic osmolytes, the abundance of HSP70 and cell turnover in the renal medulla in vivo .