Effects of bafilomycin A 1 on functional capabilities of LPS‐activated alveolar macrophages

Resident alveolar macrophages (mφ) possess plasmalemmal vacuolar‐type H + ‐ATPase (V‐ATPase) that plays a crucial role in regulation of intracellular pH (pH i ). To assess the importance of this V‐ATPase to mφ effector functions, resident alveolar mφ from rabbits were activated with E. coli ‐derived lipopolysaccharide (LPS) and exposed to bafilomycin A 1 a specific inhibitor of V‐ATPase. Bafilomycin caused a significant cytosolic acidification in both the absence and presence of CO 2 ‐HCO 3 ‐ , and in both unstimulated and activated mφ. Superoxide production and F c receptor‐mediated phagocytosis also were reduced in bafilomycin‐treated mφ. Similar effects were elicited by acidifying the cytoplasm in the absence of bafilomycin, by lowering extracellular pH (pH o ) from 7.4 to 6.5–6.6. Thus, the effects of bafilomycin on phagocytosis and superoxide production probably were related to cytosolic acidification, secondary to blockade of V‐ATPase‐mediated H + extrusion across the plasma membrane. Conversely, bafilomycin significantly increased TNF‐ α release. This effect cannot be explained by a bafilomycin‐induced acidosis because acidic pH o significantly reduced TNF‐ α release. The results demonstrate that V‐ATPase activity is an important determinant of the effector functions of LPS‐activated mφ. J. Leukoc. Biol. 57: 275–281; 1995.