title: Serum stimulates the Na+,K+ pump in quiescent fibroblasts by increasing Na+ entry.
abstract: Two ionophores (monensin and gramicidin) that carry Na+ into 3T3 cells markedly enhance the rate of 86Rb+ uptake. Ouabain prevents both ionophores from increasing 86Rb+ uptake, indicating that the ionophores activate the Na+,K+ pump. Measurements of 86Rb+ uptake and cell Na+ and K+ over a range of monensin concentrations show that the activity of the Na+,K+ pump in 3T3 cells is limited by the supply of internal Na+ and is extremely sensitive to small changes in internal Na+. Serum rapidly enhances the rate of 22Na+ uptake and net Na+ entry when Na+ exit is inhibited by ouabain. At 0.3 microgram/ml, monensin increases the rate of net Na+ entry and activates the Na+,K+ pump by the same degree as serum. The stimulation of 86Rb+ uptake by serum or the ionophores has an absolute requirement for external Na+. Thus, serum appears to stimulate the Na+,K+ pump in quiescent 3T3 cells by increasing its supply of Na+.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001769:Blood; D000001:Calcimycin / Q000494:pharmacology; D002417:Cattle; D002460:Cell Line; D003470:Culture Media; D004247:DNA / Q000096:biosynthesis; D005347:Fibroblasts / Q000378:metabolism; D006096:Gramicidin / Q000494:pharmacology; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D003470:Culture Media; D006096:Gramicidin; D014634:Valinomycin; D000001:Calcimycin; D004247:DNA; D008985:Monensin; D012964:Sodium; D012413:Rubidium; D011188:Potassium