POTENT AND SELECTIVE-INHIBITION OF NITRIC OXIDE-SENSITIVE GUANYLYL CYCLASE BY 1H-[1,2,4]OXADIAZOLO[4,3-A]QUINOXALIN-1-ONE

In brain and other tissues, nitric oxide (NO) operates as a diffusible second messenger that stimulates the soluble form of the guanylyl cyc lase enzyme and so elicits an accumulation of cGMP in target cells. In hibitors of NO synthesis have been used to implicate NO in a wide spec trum of physiological and pathophysiological mechanisms in the nervous system and elsewhere. The function of cGMP in most tissues, however, has remained obscure. We have now identified a compound, H-1-[1, 2,4]o xadiazolo[4,3-a]quinoxalin-1-one (ODQ), that potently and selectively inhibits NO-stimulated guanylyl cyclase activity. In incubated slices of cerebellum, ODQ reversibly inhibited the NO-dependent cGMP response to glutamate receptor agonists (IC50 approximate to 20 nM) but did no t affect NO synthase activity. The compound did not affect synaptic gl utamate receptor function, as assessed in hippocampal slices, nor did it chemically inactivate NO. ODQ did, however, potently inhibit cGMP g eneration in response to NO-donating compounds. An action on NO-stimul ated soluble guanylyl cyclase was confirmed in studies with the purifi ed enzyme. ODQ failed to inhibit NO-mediated macrophage toxicity, a ph enomenon that is unrelated to cGMP, nor did it affect the activity of particulate guanylyl cyclase or adenylyl cyclase. ODQ is the first inh ibitor that acts selectively at the level of a physiological NO ''rece ptor'' and, as such, it is likely to prove useful for investigating th e function of the cGMP pathway in NO signal transduction.