title: Serum stimulation of sodium transport in human fibroblasts containing low and high levels of intracellular sodium.
abstract: The relationships between intracellular sodium content, sodium transport and serum effects were investigated in human fibroblasts. In the cells with low intracellular sodium (Na+iL; 0.04 mumol sodium/mg protein), serum stimulated the sodium-potassium pump as measured by ouabain-sensitive sodium efflux and rubidium influx and also exerted a transstimulation of ouabain-insensitive sodium transport resulting in net influx. In cells with high intracellular sodium (Na+iH; 0.42 mumol sodium/mg protein) all aspects of sodium transport were increased compared to Na+iL cells. In these cells serum caused no change in sodium-potassium pump activity but significantly increased the ouabain-insensitive sodium fluxes resulting in net efflux. In Na+iL cells, serum promoted net sodium influx through an amiloride-sensitive pathway that was undetectable in the basal state. In Na+iH cells the serum-stimulated net efflux was amiloride sensitive but this pathway also contributed to a major portion of sodium transport in the basal state. This study demonstrated that sodium-potassium pump activity is directed by the supply of internal sodium and that serum can increase this supply by promoting net influx, and that serum-induced sodium transport can be modified by intracellular sodium content.
mesh_terms: D000818:Animals; D001769:Blood; D002417:Cattle; D002478:Cells, Cultured; D003470:Culture Media; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D003470:Culture Media; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium