Anion/anion exchange in human neutrophils

Abstract

Of the total one-way chloride fluxes (~1.4 meq/liter cell water. min) in steady state human polymorphonuclear leukocytes bathed in 148 mM Cl media, ~70% behaves as self-exchange mediated by a nonselective anion carrier that is not inhibited by stilbene disulfonates. Five properties of this carrier-mediated exchange were investigated: (a) substrate saturation is seen with respect to 36Cl influx as a function of the external Cl concentration [for normal-Cl cells, the apparent Km(Cl) is ~22 mM when Cl replaces para-aminohippurate (PAH) and ~5 mM when 36Cl replaces glucuronate], and with respect to 36Cl efflux as a function of the concentration of internal Cl replacing PAH [apparent Km(Cl) ≃ 35 mM for cells bathed in 148 mM Cl]; (b) there is trans stimulation of 31CI influx by internal 36Cl (replacing PAH) with an apparent Km(CI) ≃ 35 mM, and of 36Cl efflux by external C1 with an apparent Km(Cl) ≃ 22 mM (Cl replacing PAH) or ~5 mM (Cl replacing glucuronate); (c) there is substrate competition between Cl and PAH, but the carrier appears devoid of affinity for glucuronate; (d) influxes and effluxes mediated by the carrier are subject to competitive inhibition by extracellular α-cyano-4-hydroxycinnamate (CHC), with an apparent Ki ≃ 9 mM in Cl medium or ~1 mM in PAH medium (transport of the inhibitor itself is very slow); and (e) internal Cl and external Cl or PAH undergo 1:1 countertransport, which is CHC sensitive. A simple equilibrium-competition model is proposed that accounts for all the extracellular ligand interactions presented for normal-Cl cells. Least-squares values of the carrier’s true Michaelis constants for extracellular CI, PAH, and CHC are 5.03 ± 0.83, 50.3 ± 14.9, and 0.29 ± 0.09 mM, respectively. © 1986, Rockefeller University Press., All rights reserved.