Roles of superoxide dismutase in rat mast cell granules.

BACKGROUND: It has been suggested that in the granules of rat mast cells there is some kind of superoxide dismutase (SOD), but details of this SOD in mast cells remain unclear. In the present study, we studied the mode of existence of SOD in mast cells and its releasing mechanism from the granules. In addition, we discussed the physiological role of SOD in allergic events. METHODS: Purified rat mast cells were disrupted with a sonic disrupter and granules (sample I) were separated from supernatant (sample II) by centrifugation. The granules were treated with 1 mM Ca(2+), and the supernatant (sample III) was separated from the pellet (sample IV). Sample III was applied to a heparin column and the eluate was used as sample V. SOD activity was measured in these samples. RESULTS: SOD existed in mast cell granules as a heparin-binding and an inactive form. However, when granules were released and exposed to high Ca(2+) concentration, SOD was discharged from heparin and shifted to the active form. The expression of macrophage inflammatory protein-1 alpha mRNA was enhanced when hydrogen peroxide (H(2)O(2)) or sample III with the xanthine-xanthine oxidase system were added to the culture media. CONCLUSIONS: These findings suggest that in stimulated rat mast cells, the released SOD may transform the generated superoxide anion into H(2)O(2), and the generated H(2)O(2) may enhance the expression of chemokine mRNA in the mast cells.