Characterization of redox activity in resting and activated mast cells by reduction and reoxidation of lipophilic nitroxides.

1. We measured redox systems in resting and activated rat peritoneal mast cells under anoxia by using the redox metabolism of free doxyl stearic acid (5DS) and phosphatidylcholine with two 5DS molecules esterified to the glycerol (di5DSPC). 2. In the absence of oxygen, 5DS and di5DSPC were reduced to the corresponding hydroxylamines by resting mast cells, with apparent first-order kinetics of 0.085 and 0.078/min, respectively. 3. The activation of mast cells induced by compound 48/80 and bradykinin did not affect the rates of reduction of the nitroxides, and therefore the activation appeared not to be closely coupled to the redox system of these cells; this finding implies that ischemia is unlikely to affect histamine release from mast cells. 4. The oxidation of the nitroxides by the mast cells was very fast and may be nonenzymatic. 5. We concluded that nitroxides can be useful probes of redox metabolism in the mast cells but, because the characteristics of the cellular reduction-reoxidation systems differed from that of other cells, the use of this approach in other cells will require careful characterization of the redox metabolism of nitroxides in those cells.