Characteristics ofN-formyl-methionyl-leucyl-phenylalanine as an inducer of lysosomal enzyme release from human neutrophils

Abstract

N-Formyl-methionyl-leucyl-phenylalanine (FMLP) stimulated a timeand concentration-dependent release of granule associatedβ-glucuronidase and lysozyme but not cytoplasmic lactate dehydrogenase from human neutrophils. Maximum discharge of lysosomal enzymes occurred two minutes after cell contact with FMLP. The percent of total enzyme activity released is insignificant when cells are not preincubated with cytochalasin B prior to being exposed to FMLP (10⁻¹⁰-10⁻⁷ M); although 11.2 ± 1.3 and 12.4 ±1.1% of total activity forβ-glucuronidase and lysozyme, respectively, is secreted from neutrophils with 10⁻⁴ M FMLP in the absence of cytochalasin B. FMLP-stimulated release of lysosomal enzymes occurs but is significantly curtailed in the absence of extracellular calcium. Incubation of neutrophils with EGTA in calcium-free medium, however, had no effect on FMLP-elicited lysosomal enzyme extrusion. 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), a purported antagonist of intracellular calcium, demonstrated a dose-dependent inhibition of FMLP-induced release ofβ-glucuronidase and lysozyme from cytochalasin B-treated neutrophils in the absence of extracellular calcium. This effect of TMB-8 could be reversed with the addition of calcium to the extracellular medium. These studies indicate that TMB-8 may be useful in elucidating the role of calcium in the mechanism of lysosomal enzyme release.