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Abstract
PURPOSE: This study explores at which level of the guanylate cyclase pathway oxygen modulates retinal pericyte relaxation induced by nitric oxide (NO). METHODS: Bovine retinal microvascular pericytes were grown on silicone. On silicone, pericyte contractile tone induces wrinkles. Drug-induced relaxation was quantified as a reduced number of wrinkles after exposure to 3-morpholino-sydnonimine (SIN-1) or atrial natriuretic peptide (ANP) in the absence or in the presence of either 0.3 microM methylene blue (MB), a guanylate cyclase inhibitor, or 10 microM hemoglobin, a NO scavenger; and under 100% oxygen (hyperoxia), ambient air (normoxia), or 100% nitrogen (hypoxia). RESULTS: Pericytes were relaxed with SIN-1 and ANP in a concentration-dependent manner (EC50: 0.1 microM and 0.01 microM, respectively). Relaxations induced by SIN-1 or ANP were inhibited (P < 0.001) by MB, whereas hemoglobin inhibited only SIN-1 relaxations (P < 0.001). Relaxations induced by SIN-1, but not by ANP were increased (P < 0.001) under hypoxia and decreased (P = 0.002) under hyperoxia. CONCLUSIONS: SIN-1 and ANP relax pericytes through the activation of guanylate cyclase (inhibited by MB), but only SIN-1 through an extracellular release of NO (inhibited by hemoglobin). That oxygen only modulates pericyte relaxations induced by SIN-1 (NO-mediated) but not those induced by ANP suggests that an interaction between oxygen and NO might participate in the capillary network's blood-flow modulation according to local tissue oxygen tension.