Effect of ammonium on the expression of osmosensitive genes in Madin-Darby canine kidney cells.
The cells of the kidney medulla are exposed routinely to high extracellular concentrations of various solutes including NaCl, urea and ammonium (NH4+). 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 NH4+ in these cellular responses is unclear. This study thus addressed the effect of NH4+ 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 NH4Cl (50 mM; total osmolality 400 mosmol (kg H2O)(-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, NH4Cl-containing medium enhanced apoptosis compared with equiosmolar, NaCl-containing media. These results suggest that, in addition to NaCl, NH4Cl 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.
Neuhofer
Wolfgang
W
Physiologisches Institut der Universität, Pettenkoferstrasse 12, 80336 München, Germany.
Vastag
Monika
M
Fraek
Maria-Luisa
ML
Beck
Franz-X
FX
D000449:Aldehyde Reductase / Q000378:metabolism; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D004285:Dogs; D050485:GABA Plasma Membrane Transport Proteins; D005786:Gene Expression Regulation / Q000187:drug effects*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D007668:Kidney / Q000187:drug effects*; D050778:NFATC Transcription Factors; D009994:Osmolar Concentration; D011944:Receptors, Androgen / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050485:GABA Plasma Membrane Transport Proteins; D018840:HSP70 Heat-Shock Proteins; D050778:NFATC Transcription Factors; D011944:Receptors, Androgen; D014157:Transcription Factors; D000643:Ammonium Chloride; C072207:betaine plasma membrane transport proteins; D000449:Aldehyde Reductase