Effects of agents that inactivate free radical NO (NO•) on nitroxyl anion-mediated relaxations, and on the detection of NO• released from the nitroxyl anion donor Angeli's salt

1 The effects of agents that inactivate free radical nitric oxide (carboxy-PTIO, hydroxocobalamin and pyrogallol) were tested on relaxations produced by the nitroxyl anion (NO-) donor Angeli's salt in rat aortic rings and anococcygeus muscles. The amount of NO. generated from Angeli's salt in the presence of these agents was measured using a NO.-selective electrode sensor. 2 Carboxy-PTIO (100, 300 muM), hydroxocobalamin (30, 100 muM) and pyrogallol (10, 30 muM) significantly reduced relaxations produced by Angeli's salt (0.3 muM) in aortic rings but not in anococcygeus muscles. 3 NO. generated from Angeli's salt (0.1 - 10 muM), as detected by the sensor electrode, was less than 0.5% of the amount of Angeli's salt added. Carboxy-PTIO (100 muM) and hydroxocobalamin (30 muM), but not pyrogallol significantly increased the amount of NO. detected. 4 In the presence of an oxidizing agent copper [II] (as CUSO4 100 muM), the amount of NO. detected from 0.3 muM of Angeli's salt increased from an undetectable level of 142.7 +/- 15.7 nM (equivalent to 47.6% of Angeli's salt added). Under these conditions, carboxy-PTIO, hydroxocobalamin and pyrogallol significantly reduced the amount of NO. detected from Angeli's salt as well as the signal generated by an equivalent amount of authentic NO (0.33 muM). 5 The difference in effects of these agents on relaxations to Angeli's salt in the aorta and the anococcygeus muscle may be explained by the ready conversion of NO- to NO. in the aorta through an unidentified mechanism, which makes NO- susceptible to inactivation by these agents. Furthermore, in addition to inactivating NO., carboxy-PTIO and hydroxocobalamin may themselves oxidize NO- to NO., albeit slightly.