Potentiation of hyperthermia-induced haemolysis of human erythrocytes by photodynamic treatment. Evidence for the involvement of the anion transporter in this synergistic interaction.

Heat treatment of human erythrocytes led to increased passive cation permeability, followed by haemolysis. K+ leakage was linear up to a loss of about 80% in the temperature range 46-54 degrees C. Kinetic analysis of the results revealed an activation energy of 246 kJ/mol, implicating a transition in the membrane as critical step. Pretreatment of erythrocytes with 4,4'-di-isothiocyano-2,2'-stilbenedisulphonate, chymotrypsin or chlorpromazine caused a potentiation of subsequent heat-induced K+ leakage. Photodynamic treatment of erythrocytes with Photofrin II, eosin isothiocyanate or a porphyrin-Cu2+ complex as sensitizer also induced an increase in passive cation permeability, ultimately resulting in colloid osmotic haemolysis. The combination of photodynamic treatment immediately followed by hyperthermia had a synergistic effect on K+ leakage. Analysis of the results by the Arrhenius equation revealed that both the activation energy and the frequency factor of heat-induced K+ leakage were decreased significantly by preceding photodynamic treatment, suggesting that hyperthermia and photodynamic treatment have a common target for the induction of K+ leakage. Several lines of reasoning indicate that this common target is band 3. A model is thus proposed for the observed potentiation of hyperthermically induced K+ leakage by photodynamic treatment, in which photo-oxidation of band 3 results in increased sensitivity to subsequent thermal denaturation. These phenomena may be of more general significance, as photodynamic treatment and hyperthermia interacted synergistically with respect to K+ leakage with L929 fibroblasts also.