title: Effects of chronic metabolic acidosis on Na(+)-H+ exchangers in LLC-PK1 renal epithelial cells.
abstract: Porcine renal epithelial cells (LLC-PK1/clone 4) have Na(+)-H+ exchangers with different kinetic properties in their apical and basolateral membranes. cDNAs encoding the basolateral Na(+)-H+ exchanger were recently cloned. To determine whether expression of the basolateral Na(+)-H+ exchanger was affected by chronic metabolic acidosis, LLC-PK1/clone 4 cells were grown on permeant supports and incubated in control medium (pH 7.4) or acid medium (pH 6.9). After 48 h, Na(+)-H+ exchanger transport activity was measured as N-ethyl-N-isopropylamiloride (EIPA)-sensitive 22Na+ influx. Acidification caused an 84% stimulation of the transport activity of the basolateral Na(+)-H+ exchanger. The apical Na(+)-H+ exchanger was stimulated 72%, and there was no change in the EIPA-insensitive 22Na+ flux across either membrane. Stimulation of Na(+)-H+ exchange was not due to differences in intracellular pH at the time transport was assayed. To determine whether there were corresponding changes in transcript levels, poly(A)+ RNA was isolated from LLC-PK1 cells and hybridized with a cDNA encoding the basolateral Na(+)-H+ exchanger. Levels of transcripts encoding the basolateral Na(+)-H+ exchanger were increased 70% after 48 h of acidification, and there were no changes in transcripts encoding cytoskeletal gamma-actin or glyceraldehyde-3-phosphate dehydrogenase. We conclude that conditions simulating chronic metabolic acidosis coordinately increase the transport activity and transcript levels of the basolateral Na(+)-H+ exchanger in porcine renal epithelial cells.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: P
authors.initials: P
authors.lastname: Igarashi
authors.forename: M I
authors.initials: MI
authors.lastname: Freed
authors.forename: M B
authors.initials: MB
authors.lastname: Ganz
authors.forename: R F
authors.initials: RF
authors.lastname: Reilly
mesh_terms: D000138:Acidosis / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002908:Chronic Disease; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers