Involvement of cytosolic Cl- in osmoregulation of alpha-ENaC gene expression.
Hypotonicity stimulates transepithelial Na(+) reabsorption in renal A6 cells, but the mechanism for this stimulation is not fully understood. In the present study, we found that hypotonicity stimulated Na(+) reabsorption through increases in mRNA expression of the alpha-subunit of the epithelial Na(+) channel (alpha-ENaC). Hypotonicity decreases cytosolic Cl(-) concentration; therefore, we hypothesized that hypotonicity-induced decreases in cytosolic Cl(-) concentration could act as a signal to regulate Na(+) reabsorption through changes in alpha-ENaC mRNA expression. Treatment with the flavone apigenin, which activates the Na(+)-K(+)-2Cl(-) cotransporter and increases cytosolic Cl(-) concentration, markedly suppressed the hypotonicity-induced increase in alpha-ENaC mRNA expression. On the other hand, blockade of the Na(+)-K(+)-2Cl(-) cotransporter decreases cytosolic Cl(-) concentration and increased alpha-ENaC mRNA expression and Na(+) reabsorption. Blocking Cl(-) channels with 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) inhibited the hypotonicity-induced decrease in cytosolic Cl(-) concentration and suppressed the hypotonicity-induced increase in alpha-ENaC mRNA expression. Coapplication of NPPB and apigenin synergistically suppressed alpha-ENaC mRNA expression. Thus, in every case, changes in cytosolic Cl(-) concentration were associated with changes in alpha-ENaC mRNA expression and changes in Na(+) reabsorption: decreases in cytosolic Cl(-) concentration increased alpha-ENaC mRNA and increased Na(+) reabsorption, whereas increases in cytosolic Cl(-) concentration decreased alpha-ENaC mRNA and decreased Na(+) reabsorption. These findings support the hypothesis that changes in cytosolic Cl(-) concentration are an important and novel signal in hypotonicity-induced regulation of alpha-ENaC expression and Na(+) reabsorption.
Dept. of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.
Naomi
N
Niisato
Douglas C
DC
Eaton
Yoshinori
Y
Marunaka
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D047310:Apigenin; D015152:Blotting, Northern; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004594:Electrophysiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D053503:Epithelial Sodium Channels; D005110:Extracellular Space / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000502:physiology*; D009579:Nitrobenzoates / Q000494:pharmacology; D009994:Osmolar Concentration; D011794:Quercetin / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000096:biosynthesis* / Q000235:genetics; D014882:Water-Electrolyte Balance; D014982:Xenopus laevis
D002712:Chlorides; D053503:Epithelial Sodium Channels; D005419:Flavonoids; D009579:Nitrobenzoates; D012333:RNA, Messenger; D015222:Sodium Channels; C013407:benzamil; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D000584:Amiloride; D047310:Apigenin; D011794:Quercetin; D012964:Sodium