title: Enhanced Na(+)-H+ exchanger activity and NHE-1 mRNA levels in human lymphocytes during metabolic acidosis.
abstract: It has recently been demonstrated that uremic metabolic acidosis and experimental metabolic acidosis caused by ingestion of ammonium chloride coincide with increased Na(+)-H+ exchanger (NHE-1) activity in human blood cells. In the present study, we investigated whether an increased level of NHE-1 specific mRNA in human lymphocytes during the course of an experimental metabolic acidosis could explain the enhanced transport activity during metabolic acidosis. Six healthy individuals were studied before and after 5 days of taking 15 g of ammonium chloride daily. Plasma pH and bicarbonate decreased significantly, from 7.42 +/- 0.027 to 7.28 +/- 0.05 and from 26.7 +/- 2.0 to 15.6 +/- 2.9 mM, respectively. Basal cytosolic pH (pHi) and Na(+)-H+ exchange activity were measured in lymphocytes loaded with the fluorescent pHi indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Basal pHi remained unchanged during metabolic acidosis (7.03 +/- 0.07 vs. 7.03 +/- 0.06). Ethylisopropylamiloride-sensitive pHi recovery increased from 0.046 +/- 0.007 to 0.076 +/- 0.012 dpHi/min (P < 0.0001). The transcript level of NHE-1 mRNA was measured by reverse-transcription polymerase chain reaction in comparison with a constitutively expressed reference gene (glyceraldehyde-3-phosphate dehydrogenase). NHE-1 mRNA in human lymphocytes increased 1.5-fold in metabolic acidosis. These data suggest that the increased Na(+)-H+ exchange activity in metabolic acidosis may be caused by de novo synthesis of antiport protein.
authors.affiliation: Max-Planck-Institut für Biophysik, Frankfurt/Main, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Quednau
authors.forename: D
authors.initials: D
authors.lastname: Rosskopf
authors.forename: H P
authors.initials: HP
authors.lastname: Reusch
authors.forename: F C
authors.initials: FC
authors.lastname: Luft
authors.forename: W
authors.initials: W
authors.lastname: Siffert
mesh_terms: D000138:Acidosis / Q000378:metabolism*; D001345:Autoradiography; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D004996:Ethidium; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008214:Lymphocytes / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics* / Q000378:metabolism*; D013194:Staining and Labeling
chemical_list: D018076:DNA, Complementary; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D004996:Ethidium