Modes of operation of an electroneutral Na+/Li+ countertransport in human skin fibroblasts.
An elevated activity of erythrocyte Na+/Li+ countertransport (SLC) is an intermediate phenotype of human essential hypertension, but cells other than erythrocytes have not been studied. Therefore, we have examined several transport modes of Na+/Li+ exchange in human skin fibroblasts. External Na+-stimulated Li+ efflux was 152 +/- 31 (SE) nmol x mg protein(-1) x min(-1) (n = 8). At intracellular pH 7.3, intracellular Na+-stimulated Li+ influx, intracellular Li+-stimulated Na+ influx, and external Li+-stimulated Na+ efflux were very similar, indicating the presence of a tightly coupled 1:1 SLC. This pathway was not affected by 5-(N,N-dimethyl)-amiloride and changes in the membrane potential, but phloretin and intracellular acidification (intracellular pH 6.8) were markedly inhibitory. Kinetic analyses of the external Na+ site also compared with SLC, although the internal site appeared to show a low affinity for Li+. We conclude that an SLC pathway similar to that in human erythrocytes is expressed in human skin fibroblasts.
Zerbini
G
G
Division of Medicine, Scientific Institute San Raffaele, University of Milan, Italy.
Mangili
R
R
Gabellini
D
D
Pozza
G
G
D017920:Antiporters / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007474:Ion Exchange; D007700:Kinetics; D008094:Lithium / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials; D012867:Skin / Q000166:cytology / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
D017920:Antiporters; C045885:sodium-lithium countertransporter; D006859:Hydrogen; D008094:Lithium; D012964:Sodium