Factors which affect superoxide anion release from rat alveolar macrophages

In order to investigate some of the characteristics of superoxide anion release from alveolar macrophages, the effects of substances known to influence superoxide release from polymorphonuclear leukocytes (PMN) were studied in rat alveolar macrophages. There is a relatively small, but constant, amount of superoxide released from alveolar macrophages at rest. The amount released increases 5- to 6-fold and becomes maximal in about 20-30 min following exposure to unopsonized zymosan particles. The rate of superoxide release is maximal only 2 min after exposure of the cells to particles, i.e., long before particle uptake is complete. In addition to particles, release of superoxide anion can be stimulated by phorbol-12-myristate-13-acetate (PMA). Lectins and chemotactic factors, which stimulate release in PMN, have little or no effect in alveolar macrophages. Superoxide release during exposure to zymosan appears to be dependent upon extracellular Ca++. Also, the release mechanism can be affected by the addition of cyclic AMP or various protein modifiers to the medium. Since many of these findings differ from those reported by others for PMN, the control of superoxide anion release from alveolar macrophages and PMN is probably different.