Nitrite Ion Fluxes in Human Erythocytes.

Our recent studies suggest that nitrite ions serve as a storage pool of nitric oxide (NO^•) bioactivity, with reduction of nitrite to NO^• within red blood cells (RBC), thus potentially explaining endocrine effects of NO^•. We have investigated nitrite uptake and decay in human RBC using recently described methodologies based on assaying after stabilization of nitrite to reaction with hemoglobin by treatment with ferricyanide and quantificating by reductive chemiluminescence. Uptake of nitrite added to whole blood is very rapid (sec) and independent of temperature (from 4°C to 37°C) and state of oxygenation of the cells, or treatment with carbon monoxide. We obtain intracellular values as high as 711 ± 45.44 nM/l with an extracellular value of 10,935.089 ± 897.370 nM/l. Decay of nitrite levels within the RBC is, however, strongly temperature and ligand dependent. At 37°C only 22% of the original maximal value remains at 30 minutes (half life: 5.24 min), while there is no apparent decay at 4°C. Carbon monoxide also prevents nitrite destruction. If the nitrite-containing RBC are suspended in nitrite-free plasma, decay of nitrite levels is faster (half life 2.1min) suggesting export of nitrite as well as reaction with hemoglobin. We have also observed whole blood and RBC artery-to-vein gradients of nitrite levels in human forearm circulation suggesting rapid loss during RBC transit of the microcirculation. These results suggest rapid fluxes of nitrite ions into and out of RBC, as well as controlled intra-erythrocytic metabolism, which could contribute to local, rapid modulation of blood flow by mechanisms involving nitrite activation to NO^• by intra-erythrocytic hemoglobin.