INVESTIGATIONS INTO THE MECHANISM OF ACTION OF A NOVEL NITRIC-OXIDE GENERATOR ON CELLULAR RESPIRATION

Nitric oxide may regulate cellular respiration by competition with oxy gen at mitochondrial cytochrome oxidase. Using an astrocyte-derived ce ll line, we have compared the mechanism of action of the nitric oxide- generating compound Roussin's black salt with that of sodium nitroprus side on cellular oxygen consumption. Intense light exposure induced th e release of large quantities of nitric oxide from both of the donor c ompounds. However, in room light only Roussin's black salt generated l ow levels of the radical. Simultaneous measurement of oxygen consumpti on and of nitric oxide production demonstrated that sodium nitroprussi de only had inhibitory actions when exposed to intense light (nitric o xide release), whereas Roussin's black salt had inhibitory actions in room light. Extracellular haemoglobin did not prevent the inhibition o f respiration rate induced by Roussin's black salt even though stimula tion of nitric oxide release on light exposure was markedly reduced. P reincubation of cells with Roussin's black salt and subsequent measure ment of levels of light-liberated nitric oxide demonstrated that the c ompound was rapidly internalised. The uptake of sodium nitroprusside w as minimal. These data suggest that, in contrast to sodium nitroprussi de, the cellular internalisation of Roussin's black salt allows site-d irected nitric oxide release and very effective inhibition of cellular respiration.