Heme‐NO Dilates Arteries via Mobilization of NO Moieties From an Intracellular NO Store Within Vascular Smooth Muscle Cells

ABSTRACT Nitrosyl heme (heme‐NO) has recently emerged as a surrogate signaling entity for nitric oxide (NO). However, questions remain about how heme‐NO signals across the cell membrane. Herein, we test the hypothesis that extracellular heme‐NO signals as a nitrodilator that vasodilates by mobilizing NO moiety from a nitrodilator‐activated intracellular NO store (NANOS) in the vasculature. We identify a novel mechanism for glutathione‐catalyzed formation of a model compound, alb‐heme‐NO, and determine glutathione (GSH) as a ligand in its structure. Heme‐NO complexes with plasma proteins in blood and, as such, it is impermeable to red blood cells or the vascular wall. Alb‐heme‐NO‐mediated vasodilation, both ex vivo and in vivo, is attenuated by prior depletion of the NANOS and potentiated by NANOS supplementation. Incubation with alb‐heme‐NO induces efflux of NO moieties from arteries. Additionally, the role of nitrosyl hemoglobin (HbNO) in mediating NO bioactivity export from erythrocytes is challenged. In conclusion, heme‐NO functions as an extracellular nitrodilator via activation of the intracellular NANOS.