Exposure of SSRBCs to NO increases formation of stable Hb-bound NO. Total NO bound to Hb (A), SNO-Hb (B), and Hb[Fe]NO (C) was assayed by photolysis-chemiluminescence before (sham) and at varying times (in minutes) after RBC exposure to aqueous NO solution (1:250 NO:Hb ratio). Results are expressed as number of moles (S)NO per moles of Hb. Hb-bound NO in SSRBCS (SS) after exposure to NO is stable for at least 3 hours. The mean and standard error of the mean (SEM) of 3 independent experiments are shown for each set of conditions. *P < .05 for both normal RBCs (AA) and SSRBCs (SS) vs the respective sham. None of the subsequent changes from 1 to 180 minutes was statistically significant.