The effect of hypericin and hypocrellin-A on lipid membranes and membrane potential of 3T3 fibroblasts

Hypericin (HY) and Hypocrellin-A (HA) photosensitization induce rapid depol arization of plasma membrane in 3T3 cells as revealed by confocal microspec trofluorimetry using diO-C-5(3) fluorescent probe. HY and HA are also able to rigidify the lipid membrane of DMPC liposomes as indicated by the decrea se of pyrene excimer fluorescence used as a marker of the lipid membrane fl uidity. We have also observed a nonspecific inhibition of Na+,K+-ATPase act ivity due to the HY and HA photosensitization. The described effects are co ncentration- and light dose-dependent and generally more pronounced for HA than for HY, All these observations suggest that the lipid membranes can pl ay an important role in the photosensitization process induced by HY and HA at the cellular level. It can be hypothesized that for HA and HY the secon dary mechanism following type I or type II photosensitization process can b e the peroxidation of membrane lipids as well, and thus intracellular membr anes seem to be one of the most important targets of these photosensitizers . (C) 1999 Elsevier Science B.V. All rights reserved.