Gene regulation of renal-osmotic stress-induced Na-CL organic solute cotransporter.
BACKGROUND
Na- and Cl-dependent organic solute cotransporters participate in transporting neurotransmitters in the brain and organic osmolytes in the kidney.


METHODS
We examined the intranephron localization and regulation of the renal osmotic-stress-induced Na-Cl organic solute cotransporter (ROSIT) mRNA expression using microdissected nephron segments from control and dehydrated rats and RT-PCR. To further know the mechanisms of gene regulation of ROSIT, microdissected proximal straight tubules (PST) were incubated in isotonic (290 mosm/kg H2O) or hyperosmotic (490- 1,090 mosm/kg H2O) solution.


RESULTS
ROSIT mRNA was expressed predominantly in PST and to a lesser extent in cortical thick ascending limbs and cortical collecting ducts in control rats, and dehydration caused an increase in the expression in whole nephron segments. ROSIT mRNA in PST was decreased with time by incubation in isotonic solution. Incubation of PST in hypertonic solution by adding NaCl increased mRNA expression as early as 15 min (1.5- and 3-fold at 15 and 30 min, respectively). This stimulating effect of NaCl was largest at 890 mosm/kg H2O. Hypertonicity by mannitol or myoinositol also increased ROSIT mRNA expression. In contrast, hyperosmolality by urea reduced ROSIT mRNA expression. GAPDH mRNA expression, an internal standard, did not change by incubation in NaCl or mannitol solution.


CONCLUSIONS
In summary, ROSIT mRNA expression was most abundant in PST in control and it was stimulated in whole nephron segments by dehydration. ROSIT mRNA expression in PST was stimulated by hypertonicity but not by urea. These data suggest that ROSIT may participate in the transport of amino acid under control conditions and organic osmolytes in dehydration.
Baba
Tomoko
T
Department of Nephrology, Kumamoto University Graduate School of Medical Sciences, Honjo, Kumamoto, Japan.
Nonoguchi
Hiroshi
H
Itoh
Kazuko
K
Nakayama
Yushi
Y
Kohda
Yukimasa
Y
Inoue
Takeaki
T
Tomita
Kimio
K
D000818:Animals; D001769:Blood; D046508:Culture Techniques; D003681:Dehydration; D004234:Diuretics, Osmotic / Q000494:pharmacology; D005786:Gene Expression Regulation; D007294:Inositol / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D009399:Nephrons / Q000737:chemistry / Q000378:metabolism*; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D014508:Urea / Q000494:pharmacology; D014556:Urine / Q000737:chemistry
D004234:Diuretics, Osmotic; D012333:RNA, Messenger; C089982:Slc6a18 protein, rat; D027981:Symporters; D008353:Mannitol; D012965:Sodium Chloride; D007294:Inositol; D014508:Urea