Extra- and intracellular Ca2+ requirements for lysosomal enzyme secretion in human neutrophils

Abstract

Ca²⁺-EGTA combinations were utilized in Hank's buffers to fix extracellular free Ca²⁺ concentrations [Ca²⁺ _f] for the study of human neutrophil lysosomal enzyme secretion. Ca²⁺-dependent neutrophil secretion initiated by formyl-methionyl-leucyl-phenylalanine (FMLP) and C5a required small amounts of [Ca²⁺ _f] (1–3×10⁻⁶ M) while that caused by ionophore A23187 required 10⁻⁵ M or greater [Ca²⁺ _f]. The inhibition of FMLP- and C5a-induced lysosomal enzyme secretion by the intracellular Ca²⁺ antagonist, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) was additive to lowering extracellular [Ca²⁺ _f] from 10⁻⁴ M to 10⁻⁶ M or blocking plasma membrane Ca²⁺ flux with verapamil. These results suggest that extracellular and intracellular Ca²⁺ flux may be coupled in the initiation of neutrophil secretion caused by FMLP and C5a.