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

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 x 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.