Chemotactic factor-induced activation of Na+/H+ exchange in human neutrophils. II. Intracellular pH changes.
The intracellular pH (pHi) changes resulting from chemotactic factor-induced activation of Na+/H+ exchange in isolated human neutrophils were characterized. Intracellular pH was measured from the equilibrium distribution of [14C]-5,5-dimethyloxazolidine-2,4-dione and from the fluorescence of 6-carboxyfluorescein. Exposure of cells to 0.1 microM N-formyl-methionyl-leucyl-phenylalanine (FMLP) in 140 mM Na+ medium at extracellular pH (pHo) 7.40 led to a rise in pHi along an exponential time course (rate coefficient approximately 0.55 min-1). By 10 min, a new steady-state pHi was reached (7.75-7.80) that was 0.55-0.60 units higher than the resting pHi of control cells (7.20-7.25). The initial rate of H+ efflux from the cells (approximately 15 meq/liter X min), calculated from the intrinsic intracellular buffering power of approximately 50 mM/pH, was comparable to the rate of net Na+ influx (approximately 17 meq/liter X min), an observation consistent with a 1:1 stoichiometry for Na+/H+ exchange. This counter-transport could be inhibited by amiloride (apparent Ki approximately 75 microM). When either the external ([Na+]o) or internal Na ([Na+]i) concentrations, pHo, or pHi were varied independently, the new steady-state [Na+]i and pHi values in FMLP-stimulated cells were those corresponding to a chemical equilibrium distribution of Na+ and H+ across the cell membrane. By analogy to other activated cells, these results indicate that an alkalinization of pHi in human neutrophils is mediated by a chemotactic factor-induced exchange of internal H+ for external Na+.
D000584:Amiloride / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood*; D005452:Fluoresceins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007424:Intracellular Fluid; D007700:Kinetics; D008744:Methylamines; D008985:Monensin / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000097:blood / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D005452:Fluoresceins; D007202:Indicators and Reagents; D008744:Methylamines; D017923:Sodium-Hydrogen Exchangers; C024098:6-carboxyfluorescein; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000584:Amiloride; D008985:Monensin; D012964:Sodium; C023336:trimethylamine