PHOTODYNAMIC EFFECTS INDUCED BY FUROCOUMARINS ON A MEMBRANE SYSTEM. COMPARISON WITH HEMATOPORPHYRIN

Abstract Isolated rat liver mitochondria have been used as a model to investigate the photodynamic action of psoralen (Ps) and 4,5',8-trimethylpsoralen (TMP) on cellular membrane systems in comparison with hematoporphyrin (Hp). Oxidation was detected by the consumption of free oxygen as measured polarographically in the respiratory chamber when irradiated with UV light (320-380 nm). In the presence of Ps, singlet oxygen was produced in the respiratory medium but neither the respiration nor the oxidative phosphorylation were affected. On the contrary the hydrophobic derivative TMP impaired the respiration with rapid uncoupling of oxidative phosphorylation as did Hp. The ineffectiveness of Ps as well as the effectiveness of TMP vs. Hp is explained on the basis of photophysical properties of the molecules and their partition coefficient. These results may indicate that, in the photochemiotherapy of skin diseases, furocoumarins can drive photodynamic reactions at various subcellular levels according to their hydrophobicity.