ROLE OF HYDROXYL RADICAL IN THE OXIDANT H2O2-MEDIATED CA2-MUSCLE MITOCHONDRIA( RELEASE FROM PULMONARY SMOOTH)

We sought to investigate the mechanism(s) by which the oxidant H2O2 st imulates Ca2+ release from mitochondria of bovine pulmonary vascular s mooth muscle tissue and to test the hypothesis that hydroxyl radical i s involved in this phenomenon. Treatment of the smooth muscle tissue w ith 1 mM H2O2 dramatically stimulated hydroxyl radical generation as m easured by methane (CH4) production by GLC using dimethylsulfoxide (DM SO) as the substrate. Pretreatment of the mitochondria with the hydrox yl radical scavanger dimethylthiourea (DMTU) prevented the increase in CH4 production caused by H2O2. In the absence of ECTA, H2O2 caused st imulation of Ca2+ release from mitochondria occurred with a lag time o f about 4 min. Addition of EGTA to Ca2+ loaded mitochondria resulted a n immediate loss of Ca2+ and that has been found to be augmented by H2 O2. The release of Ca2+ by H2O2 did not appear to occur with concommit ant increase in sucrose entry into, K+ release from, and swelling of m itochondria when the Ca2+ cycling was prevented by EGTA. These observa tions suggested that H2O2-mediated Ca2+ release from bovine pulmonary vascular smooth muscle tissue mitochondria occurred (i) through the in volvement of hydroxyl radical; (ii) via specific pathway(s); and (iii) did not appear to happen primarily via nonspecific 'pore' formation.