title: Regulation of nitrite transport in red blood cells by hemoglobin oxygen fractional saturation.
abstract: Allosteric regulation of nitrite reduction by deoxyhemoglobin has been proposed to mediate nitric oxide (NO) formation during hypoxia. Nitrite is predominantly an anion at physiological pH, raising questions about the mechanism by which it enters the red blood cell (RBC) and whether this is regulated and coupled to deoxyhemoglobin-mediated reduction. We tested the hypothesis that nitrite transport by RBCs is regulated by fractional saturation. Using human RBCs, nitrite consumption was faster at lower fractional saturations, consistent with faster reactions with deoxyheme. A membrane-based regulation was suggested by slower nitrite consumption with intact versus lysed RBCs. Interestingly, upon nitrite addition, intracellular nitrite concentrations attained a steady state that, despite increased rates of consumption, did not change with decreasing oxygen tensions, suggesting a deoxygenation-sensitive step that either increases nitrite import or decreases the rate of nitrite export. A role for anion exchanger (AE)-1 in the control of nitrite export was suggested by increased intracellular nitrite concentrations in RBCs treated with DIDS. Moreover, deoxygenation decreased steady-state levels of intracellular nitrite in AE-1-inhibited RBCs. Based on these data, we propose a model in which deoxyhemoglobin binding to AE-1 inhibits nitrite export under low oxygen tensions allowing for the coupling between deoxygenation and nitrite reduction to NO along the arterial-to-venous gradient.
authors.affiliation: Dept. of Pathology, Univ. of Alabama at Birmingham, 901 19th St. S., BMR-2, Rm. 302, Birmingham, AL 35294, USA.
authors.forename: Dario A
authors.initials: DA
authors.lastname: Vitturi
authors.forename: Xinjun
authors.initials: X
authors.lastname: Teng
authors.forename: José C
authors.initials: JC
authors.lastname: Toledo
authors.forename: Sadis
authors.initials: S
authors.lastname: Matalon
authors.forename: Jack R
authors.initials: JR
authors.lastname: Lancaster
authors.forename: Rakesh P
authors.initials: RP
authors.lastname: Patel
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D001457:Anion Exchange Protein 1, Erythrocyte / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia / Q000097:blood*; D007700:Kinetics; D008706:Methemoglobin / Q000378:metabolism; D008955:Models, Cardiovascular; D009569:Nitric Oxide / Q000097:blood; D009573:Nitrites / Q000097:blood*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism*; D014664:Vasodilation
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D006454:Hemoglobins; D009573:Nitrites; D010108:Oxyhemoglobins; D009569:Nitric Oxide; C100003:deoxyhemoglobin; D008706:Methemoglobin; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D010100:Oxygen