Intracellular or extracellular calcium can be used to trigger C5a-stimulated enzyme secretion from rabbit neutrophils

The ability of C5a to stimulate lysosomal enzyme release and ⁴⁵Ca²⁺ efflux from rabbit neutrophils was studied. C5a stimulated β-glucuronidase release from cytochalasin B-treated neutrophils either in the presence or absence of extracellular calcium. Depletion of cell calcium by pretreatment with the calcium ionophore A23187 blocked both the ability of C5a to elicit enzyme release in the absence of extracellular calcium and its ability to stimulate ⁴⁵Ca²⁺ efflux. Both actions were dose-dependent over the same concentration range (10^-8-10^-6 M ionophore A23187). In contrast, ionophore pretreatment had no effect on C5a-stimulated enzyme release in the presence of extracellular calcium. These results suggest that (a) release of cell calcium is required for enzyme secretion in the absence of extracellular calcium, and (b) C5a can trigger near-maximal enzyme release by using calcium from either of two sources: the extracellular space or an intracellular site.