Renal epithelial cell growth can occur in absence of Na+-H+ exchanger activity.
An electroneutral Na+-H+ exchange system has been described in a variety of tissues and cell types, including those of renal origin, and has been proposed to play a role in the activation of growth. We have recently characterized the presence of this ubiquitous transporter in the apical domain of confluent epithelial LLC-PK1 cells (J. Biol. Chem. 261: 3252-3258, 1986). Because most apical membrane proteins appear late in cell growth, accompanying epithelial cell polarization, we determined whether the Na+-H+ exchanger is required for the growth of LLC-PK1 cells. The studies reported here show that there is no obligatory requirement for increased H+ efflux or Na+ entry via the Na+-H+ exchanger for the initiation of cell growth in this epithelial cell line. We used 22Na+ influx, acid extrusion, and intracellular pH determinations to show that onset of cell growth, as measured by DNA content, precedes the activity of the Na+-H+ exchanger in exponentially growing cells, whereas confluent monolayers express Na+-H+ exchanger activity. When confluent cells are replated at low density, Na+-H+ exchanger activity disappears within 8 h in contrast to high-density replated cells. The fact that Na+-H+ exchanger activity is only present in confluent monolayers suggests that the development of tight junctions and polar differentiation play a role in the expression of the Na+-H+ exchanger and that this exchanger is more important to the polar epithelial cell for transepithelial transport than for the maintenance of intracellular pH.
Mohrmann
M
M
Department of Medicine, Massachusetts General Hospital, Boston.
Cantiello
H F
HF
Ausiello
D A
DA
D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D001839:Bombesin / Q000494:pharmacology; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology* / Q000187:drug effects; D011189:Potassium Chloride / Q000494:pharmacology; D011522:Protons; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D004815:Epidermal Growth Factor; D011189:Potassium Chloride; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D004247:DNA; D012964:Sodium; D001839:Bombesin