Extracellular ATP-induced production of hydrogen peroxide in porcine thyroid cells.
Hydrogen peroxide (H2O2) is an essential substrate for the peroxidase reaction in thyroid hormone biosynthesis. We demonstrated the production of H2O2 from porcine thyroid cells stimulated with extracellular ATP, using a scopoletin-horseradish peroxidase (HRP) system. Incubation of isolated cells for 1 day in the presence of 10% (v/v) newborn calf serum was necessary for the detection of induction by ATP of H2O2 production. The rate of H2O2 production induced by the addition of ATP increased in a dose-dependent manner, and the concentration of ATP required for half-maximum stimulation was about 10 mumol/l. ADP and GTP were also effective, but only at higher concentrations than ATP. In the absence of extracellular Ca2+, the production rate was very low. Production of H2O2 from thyroid cells was also measured by a method which discriminated between H2O2 and superoxide anion (O2-); in this, diacetyldeuteroheme-substituted HRP was employed as the trapping agent for both O2 metabolites. The thyroid cells produced H2O2, but not O2-, when the cells were stimulated by extracellular ATP.