Pharmacology of the nitric oxide receptor, soluble guanylyl cyclase, in cerebellar cells

1 The nitric oxide (NO) receptor, soluble guanylyl cyclase (sGC), is commonly manipulated pharmacologically in two ways. Inhibition of activity is achieved using 1-H-[1.2,4]oxadiazolo[4,3a]quinoxalin-1-one (ODQ) which oxidizes the haem prosthetic group to which NO binds, while the compound 3-(5-hydroxymethyl-2-furyl)-1-benzylindazole (YC-1) is considered an 'allosteric' activator. Knowledge of how these agents function and interact in a normal cellular environment is limited. These issues were addressed using rat cerebellar cells. 2 Inhibition by ODQ was not simply competitive with NO. The rate of onset was ODQ concentration-dependent and developed in two kinetic phases. Recovery from inhibition occurred with a half-time of similar to5 min. 3 YC-1 slowed the rate at which sGC deactivated on removal of NO by 45 fold. consistent with YC-1 increasing the potency of NO for sGC. YC-1 also enhanced the maxitnal response to NO by 2 fold. Furthermore, when added to cells in which sGC was 90% desensitized. YC-1 abruptly enhanced sGC activity to a degree that indicated partial reversal of desensitization. 4 After pre-exposure to YC-1, sGC became resistant to inhibition by ODQ. In addition, YC-1 rapidly reversed inhibition by ODQ in cells and for purified sGC. suggesting that YC-1 either increases the NO affinity of the oxidized sGC haem or reverses haem oxidation. 5 It is concluded that the actions of ODQ and YC-1 on sGC are broadly similar in cells and purified preparations. Additionally, YC-1 transiently reverses sGC desensitization in cells. It is hypothesized that YC-1 has multiple actions on sGC, and thereby both modifies the NO binding site and enhances agonist efficacy.