The Relative Role of Soluble Guanylyl Cylase Dependent and Independent Pathways in Nitric Oxide Inhibition of Platelet Aggregation Under Flow

Endothelial cell derived nitric oxide (NO) inhibits the activation and aggregation of platelets. NO inhibition occurs through the intracellular receptor soluble guanylyl cyclase (sGC)-dependent pathways, but there is also evidence of sGC-independent pathways at high NO concentrations. In this study, we integrated a NO-releasing polymer into a microfluidic vascular injury model to measure the relative roles of sGC-dependent and sGC-independent pathways as a function of NO flux and shear rate. Whole blood was perfused at 200–1000 s −1 over collagen with NO wall fluxes of 0.4 and 6.8 × 10 −10 mol cm −2 min −1 , and 1 H -[1,2,4]oxadiazolo[4,3- a ]quinoxalin-1-one (ODQ) was used to inhibit sGC. A sGC-independent pathway dominated inhibition of platelet aggregation at high NO flux, while the sGC-dependent pathway dominated at low NO flux independent of shear rate. Experiments performed with inhibitors of thrombin or an antagonist of the ADP receptor P2Y 12 showed that platelet aggregation was primarily driven by ADP, but that the sGC-independent pathway dominated in both cases at high NO flux. These data suggest that a sGC-independent pathway may play an important role under conditions where NO flux is elevated such as inducible nitric oxide mediated NO production at the site of a vascular injury.