Secretion of granule enzymes from alveolar macrophages : Regulation by intracellular Ca-buffering capacity

Rabbit alveolar macrophages exposed to the ionophore A23187 in the presence of extracellular Ca²⁺ take up about 12 nmoles of Ca²⁺/1 × 10⁶ cells. This uptake induces a slight, but significant, extracellular release of granule enzymes, β-glucuronidase and lysozyme, but not of the cytoplasmic marker, lactate dehydrogenase. If either EGTA is added to the medium or Mg²⁺ replaces Ca²⁺ no stimulation of secretion is observed. If the energy supply is decreased by treating the macrophages with mitochondrial inhibitors such as oligomycin, cyanide, or rotenone and antimycin, Ca²⁺-dependent secretion is potentiated several fold. Selective release of granule enzymes from macrophages exposed to A23187 and Ca²⁺ is also stimulated by cytochalasin B (CB).