Properties of the principal anion-exchange mechanism in human neutrophils

As part of our ongoing studies aimed at understanding the physiology of human neutrophil function, we have been investigating the nature of the principal anion-exchange mechanism in these cells. This countertransport system functions physiologically as a Cl-/HCO3- exchanger in intracellular pH regulation from alkalinization (Simchowitz and Roos, 1985). In summarizing the results of our work, it is worthwhile to keep in mind the well-defined properties of the classic inorganic anion-exchange carrier of red blood cells, as important differences between the two are evident. Inhibitor Profile In our original articles on Cl- movements (Simchowitz and De Weer, 1986; Simchowitz et al., 1986), we had identified CHC, which suppresses monocarboxylate transport in mitochondria (Halestrap and Denton, 1975), as a relatively weak inhibitor. Several structural analogues, including alpha-methylcinnamate and alpha-phenylcinnamate, exhibited enhanced activity against anion exchange. The most potent compound thus far identified was UK-5099, which was approximately 300-fold more active than CHC. The inhibitory effect of each member of this series of compounds was strictly competitive in nature: both the drug and Cl ions appeared to bind to the same external translocation site on the exchange carrier. The inhibition by several other unrelated agents (e.g., MK-473, niflumate, flufenamate, and NAP-taurine), all weak organic acids, was also of the competitive type, which suggests that these compounds bind to the carrier by virtue of their negatively charged carboxyl or sulfonic groups. In marked contrast to erythrocytes, the anion-exchange carrier of neutrophils is rather insensitive to the disulfonic stilbenes SITS and DIDS (Simchowitz and De Weer, 1986): little or no effect can be detected in 148 mM Cl-. However, under conditions of low external Cl- (5-35 mM), SITS can in fact be shown to interact weakly with the anion binding site of the exchange carrier. In a comparable vein, several other drugs, all of which have been reported to suppress Cl- fluxes in red cells (for reviews, see Sachs et al., 1975; Gunn, 1979; Knauf, 1979; Lowe and Lambert, 1983), were either completely inactive against anion exchange in neutrophils at a concentration of 1 mM or only marginally effective at doses several orders of magnitude greater than those required in red blood cells. This list included furosemide, picrylsulfonate, maleic anhydride, 5,5'-dithio-bis(2-nitrobenzoate), salicylate, 2-methoxy-5-nitrotropone, and aldrithiol.4+he external