Erythroid anion Exchanger-1 (band 3) transports nitrite for nitric oxide metabolism.

Nitrite (NO) interacts with hemoglobin (Hb) in various ways to regulate blood flow. During hypoxic vasodilation, nitrite is reduced by deoxyHb to yield nitric oxide (NO). While NO, a hydrophobic gas, could freely diffuse across the cell membrane, how the reactant nitrite anion could permeate through the red blood cell (RBC) membrane remains unclear. We hypothesized that Cl/HCO anion exchanger-1 (AE1; band 3) abundantly embedded in the RBC membrane could transport NO, as HCO and NO exhibit similar hydrated radii. Here, we monitored NO/NO generated from NO inside human RBCs by DAF-FM fluorophore. NO, not NO, increased intraerythrocytic DAF-FM fluorescence. To test the involvement of AE1-mediated transport in intraerythrocytic NO/NO production from nitrite, we lowered Cl or HCO in the RBC-incubating buffer by 20 % and indeed observed slower rise of the DAF-FM fluorescence. Anti-extracellular AE1, but not anti-intracellular AE1 antibodies, reduced the rates of NO formation from nitrite. The AE1 blocker DIDS similarly reduced the rates of NO/NO production from nitrite in a dose-dependent fashion, confirming that nitrite entered RBCs through AE1. Nitrite inside the RBCs reacted with both deoxyHb and oxyHb, as evidenced by 6.1 % decrease in deoxyHb, 14.7 % decrease in oxyHb, and 20.7 % increase in methemoglobin (metHb). Lowering Cl in the milieu equally delayed metHb production from nitrite-oxyHb and nitrite-deoxyHb reactions. Thus, AE1-mediated NO transport facilitates NO-Hb reactions inside the red cells, supporting NOx metabolism in circulation.