Chloride movements in human neutrophils. Diffusion, exchange, and active transport.

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Abstract
Chloride content and fluxes were measured in isolated resting human peripheral polymorphonuclear leukocytes. The intracellular Cl concentration of cells kept at 37.degree. C in 148 mM Cl media was .apprx. 80 meq/liter cell water, fourfold higher than expected for passive distribution at the cell''s estimated membrane potential (approximately -53 mV). All intracellular Cl was rapidly exchangeable with external 36Cl. Cells lost Cl exponentially into Cl-free media, and reaccumulated it when Cl was restored to the bath; this reuptake was dependent on metabolism. One-way 36Cl fluxes in steady state cells were .apprx. 1.4 meq/liter .cntdot. min. The bulk (.apprx. 70%) of these represented electrically silent Cl/Cl exchange mediated by a carrier insensitive to disulfonic stilbenes but blocked by the anion carrier inhibitor .alpha.-cyano-4-hydroxycinnamate (CHC). The remaining fluxes were characterized in some detail. About 20% of 36Cl influx behaved as active transport: it moved thermodynamically uphill and was absent in cells treated with 2-deoxy-D-glucose, displayed Michaelis-Menten kinetics with Km(Cl) .simeq. 5 mM, Vmax .simeq. 0.25 meq/lite .cntdot. min, and was inhibited by CHC (Ki .simeq. 1.7 mm), ethacrynate (Ki .simeq. 50 .mu.m), and furosemide (Ki .simeq. 50 .mu.M). About 30% of Cl efflux and .apprx. 8% of Cl influx behaved as electrodiffusion through a low-permeability pathway (PCl .simeq. 4 .times. 10-9 cm/s; gCl .simeq. 1 .mu.S/cm2; PK/PNa/PCl .simeq. 10:1:1); these fluxes were linear with concentration and strongly voltage sensitive. The putative Cl channel does not appear to be voltage gated, and gives evidence of single filing.