Chemotactic factor-induced activation of Na+/H+ exchange in human neutrophils. I. Sodium fluxes.
The nature of Na+ fluxes in resting and in chemotactic factor-activated human neutrophils was investigated. In resting cells, ouabain-insensitive unidirectional 22Na+ in- and effluxes represented passive electrodiffusional fluxes through ion channels: they were nonsaturable and voltage-dependent (PNa = 4.3 X 10(-9) cm/s). Amiloride (1 mM) had little effect on resting 22Na+ influx (approximately 0.8 meq/liter X min), thereby suggesting a minor contribution of Na+/H+ exchange and a lack of amiloride-sensitive Na+ channels. When neutrophils were exposed to the chemotactic tripeptide N-formyl-methionyl-leucyl-phenylalanine (FMLP, 0.1 microM), 22Na+ influx was stimulated approximately 30-fold (initial rate approximately 22 meq/liter X min). The FMLP-induced 22Na+ influx was saturable with respect to external Na+ (Km 26-35 mM, Vmax approximately 28 meq/liter X min), was electroneutral, and could be competitively inhibited by amiloride (Ki 10.6 microM). From a resting value of approximately 30 meq/liter of cell water, internal Na+ in FMLP-stimulated cells rose exponentially to reach a concentration of approximately 60 meq/liter by 10-15 min. This uptake was blocked by amiloride. FMLP also stimulated the efflux of 22Na+ which followed a single exponential time course (rate coefficient approximately 0.16 min-1). The FMLP-induced 22Na+ fluxes were similar to those observed with 10 microM monensin, a known Na+/H+ exchanging ionophore. The data indicate that FMLP activates an otherwise quiescent, amiloride-sensitive Na+/H+ exchange. Furthermore, all of the FMLP-induced 22Na+ fluxes can be satisfactorily accounted for by transport through the exchanger, leaving little room for an appreciable increase in Na+ conductance.
D000584:Amiloride / Q000494:pharmacology; D002352:Carrier Proteins / Q000097:blood*; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000097:blood; D004073:Digitoxigenin / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials; D008985:Monensin / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; D004073:Digitoxigenin; C017227:20,22-dihydrodigitoxigenin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D010042:Ouabain; D000584:Amiloride; D008985:Monensin; D012964:Sodium; D011188:Potassium