CHEMOTACTIC FACTOR-INDUCED ACTIVATION OF NA+/H+ EXCHANGE IN HUMAN-NEUTROPHILS .1. SODIUM FLUXES

  • 1 January 1985
    • journal article
    • research article
    • Vol. 260  (24) , 3237-3247
Abstract
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 .times. 10-9 cm/s). Amiloride (1 mM) had little effect on resting 22Na+ influx (.apprx. 0.8 meq/liter .cntdot. 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 .mu.M), 22Na+ influx was stimulated .apprx. 30-fold (initial rate .apprx. 22 meq/liter .cntdot. min). The FMLP-induced 22Na+ influx was saturable with respect to external Na+ (Km 26-35 mM, Vmax .apprx. 28 meq/liter .cntdot. min), was electroneutral, and could be competitively inhibited by amiloride (Ki 10.6 .mu.M). From a resting value or .apprx. 30 meq/liter of cell water, internal Na+ in FMLP-stimulated cells rose exponentially to reach a concentration of .apprx. 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 .apprx. 0.16 min-1). The FMLP-induced 22Na+ fluxes were similar to those observed with 10 .mu.M 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.

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