Relationship between intracellular ionic strength and expression of tonicity-responsive genes in rat papillary collecting duct cells
Intracellular ionic strength may play an important role in regulating the expression of genes encoding osmolyte-accumulating molecules. To establish whether a strict relation exists between these variables, intracellular ionic strength (sum of Na + , Cl â and K + concentrations) and the relative a...
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Published in | The Journal of physiology Vol. 543; no. 1; pp. 147 - 153 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
The Physiological Society
15.08.2002
Blackwell Publishing Ltd Blackwell Science Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Intracellular ionic strength may play an important role in regulating the expression of genes encoding osmolyte-accumulating
molecules. To establish whether a strict relation exists between these variables, intracellular ionic strength (sum of Na + , Cl â and K + concentrations) and the relative abundance of mRNA derived from various tonicity-sensitive genes was examined using electron
microprobe analysis and Northern blots on primary cultures of rat papillary collecting duct (PCD) cells following acute or
long-term alterations in medium tonicity. Hypertonic medium (450 mosmol kg â1 ) evoked an initial rise in intracellular ionic strength (269 ± 5 vs. 194 ± 7 mmol (kg wet weight (wt)) â1 in isotonic controls; means ± s.e.m. ), which subsequently declined gradually, and a significantly higher abundance of bgt1 (Na + - and Cl â -dependent betaine transporter), smit (Na + / myo -inositol cotransporter), ar (aldose reductase) and osp94 (osmotic stress protein 94) mRNAs. Conversely, exposure to hypotonic medium (200 mosmol kg â1 ) for 12 h was associated with significantly reduced intracellular ionic strength (153 ± 4 mmol (kg wet wt) â1 ) and significantly reduced the abundance of smit and ar mRNAs. PCD cells preconditioned in hypotonic medium and re-exposed to isotonic medium showed significantly higher abundance
of these mRNAs than isotonic controls, although the intracellular ionic strength did not differ. Two further tonicity-sensitive
genes responded differently to medium tonicity: while the abundance of hsp70 (heat shock protein 70) mRNA increased significantly following both hypo- and hypertonic stress, inos (inducible nitric oxide synthase) mRNA abundance correlated inversely with medium tonicity. These findings support the view
that the effect of intracellular ionic strength on the expression of bgt1, smit, ar and osp94 is modulated by additional factors such as cell volume, and that its effect on the pathways regulating hsp70 and inos is even more complex. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2002.021931 |