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

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.