Anion channel blockers inhibit lysosomal enzyme secretion from human neutrophils without affecting generation of superoxide anion

Abstract

The role of permeant anions in lysosomal enzyme secretion from human neutrophils was investigated by means of anion-channel-blocking agents: 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), and pyridoxal phosphate. Lysosomal enzyme release from cytochalasin B-treated human neutrophils stimulated by immune complexes (bovine serum albumin and IgG anti-bovine serum albumin) was inhibited by DIDS, SITS, and pyridoxal phosphate at concentrations that inhibited sulfate fluxes. Enzyme secretion triggered by calcium ionophore A23187 was also inhibited by DIDS and SITS; these agents acted on secretory events subsequent to Ca2+ influx. Neither the species of permeant anion(s) nor the role of anion fluxes in degranulation was identified, although influxes of chloride, hydroxide, or phosphate ions were not critical. In contrast to degranulation, generation of superoxide anions (O2.-) stimulated by immune complex or A23187 was not inhibited by these agents. Ultrastructural cytochemical studies demonstrated that, although lysosomal contents were not discharged from stimulated cells, vacuole formation and lysosome-lysosome fusion were unaffected by SITS or DIDS. Data suggest that anion channel blockers specifically inhibit fusion of lysosomes with the plasma membrane or its invaginations.