PHOTOMODIFICATION OF HUMAN ERYTHROCYTES: EXTERNAL HEAVY ATOM EFFECT, SELECTIVE PERMEABILITY AND PROPERTIES OF THE ANION PERMEATION PATHWAY

Abstract— Anion permeability was studied in normal and photomodified erythrocytes and the role of anion species in photomodification and singlet oxygen generation was evaluated. Relative permeability to halides and nitrate was assessed using lysis rates in valinomycin-treated cells to make anion permeation rate-limiting. In non-photomodified cells the normal high temperature dependence (E:, = 67 kJ/mol; 16 kcalhol), selectivity sequence (NO, > I > Br > F > Cl) and sensitivity to block by the stilbene derivative HzDIDS were confirmed. In cells photomodified by illumination in the presence of phloxine B the anion permeability was severely perturbed. The temperature dependence was strongly reduced, the permeability to ions other than fluoride increased, leading to a reversal of the F/CI selectivity, and the capacity to be blocked by HIDIDS was lost. Pretreatment with NEM and posttreatment with DTE did not affect rates of photohemolysis. The amount of photomodification varied with species of anion present in the reaction medium, being greatest for F and smallest for I. Rates of singlet oxygen generation in aqueous solution measured by the RNO bleaching method followed the same anion sequence, suggesting a strong external heavy atom effect.