title: The amiloride-sensitive Na+/H+ antiport in 3T3 fibroblasts.
abstract: BALB/c 3T3 fibroblasts have an amiloride-sensitive Na+ uptake mechanism which is hardly detectable under normal physiological conditions. The activity of this Na+ transport system can be increased to a large extent by treatments that decrease the internal pH such as loss of intracellular NH4+ as NH3 or incubation with nigericin in the presence of a low external K+ concentration. These treatments have made possible an analysis of the interaction of the Na+/H+ antiport with amiloride and of the external pH dependence of the system. The addition of fetal bovine serum to quiescent 3T3 cells stimulates the initial rate of the amiloride-sensitive 22Na+ uptake by only 50%. However, after treatment of the cells with ammonia or nigericin, serum produces a 40-fold stimulation of the rate of the amiloride-sensitive 22Na+ uptake. Control experiments show that serum does not stimulate the activity of the Na+/H+ antiport by an indirect mechanism involving a depolarization of the membrane or a modification of the internal Ca2+ concentration. It is suggested that some serum component directly interacts with the Na+/H+ exchanger to modify its catalytic properties.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D005312:Fetal Blood; D005347:Fibroblasts / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D009550:Nigericin / Q000494:pharmacology; D011719:Pyrazines / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D011719:Pyrazines; D000644:Quaternary Ammonium Compounds; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; D009550:Nigericin