| Abstract: | In an attempt to understand better the molecular basis for the enhanced respiratory burst of activated macrophages (M phi), we investigated the relationship between stimulus-induced changes in membrane potential and release of superoxide anion (O2-) in mouse peritoneal M phi. Resident M phi and M phi elicited by injection of lipopolysaccharide (LPS-M phi) or obtained from animals infected with bacille Calmette-Guérin (BCG-M phi) were used. LPS-M phi and BCG-M phi showed more pronounced changes in membrane potential (depolarization) and greater release of O2- on contact with phorbol myristate acetate (PMA) than did resident macrophages. The lag time between addition of stimulus and onset of release of O2- was reduced in activated compared with resident cells. Membrane potential changes began 60 to 90 sec before release of O2- could be detected in each cell type. The dose-response curves for triggering of membrane potential changes and O2- release by PMA were identical. The magnitude of membrane potential changes and of O2- release in LPS-M phi and BCG-M phi declined progressively during in vitro culture, and values on day 3 approached those in resident macrophages ("deactivation"). Extracellular glucose was required for effective stimulated change in membrane potential and O2- release. These findings indicate that membrane potential changes are closely associated with O2- -releasing capacity in macrophages, and that the systems that mediate membrane potential changes and production of O2- develop or decline concomitantly during activation or deactivation of the cells. Although the plasma membrane was highly depolarized by high extracellular K+ or by the sodium ionophore gramicidin, O2- release was not induced by these maneuvers, indicating that changes in membrane potential by themselves are not sufficient to trigger the respiratory burst in macrophages. Release of O2- was not impaired in buffers in which Na+ was completely replaced with equimolar concentrations of K+ or choline+; thus, induction or maintenance of the respiratory burst in M phi does not require an influx of Na+. |
