IMPAIRMENT OF RED CELL MEMBRANE CYTOSKELETON BY PROTOPORPHYRIN‐IX: LIGHT AND DARK EFFECTS

Abstract— Membrane cytoskeletons were separated by use of TritonX–100 from freshly isolated red cells, fixed with glutaraldehyde and their morphology was followed by scanning electron microscopy. At 37°C and pH 6.5 cytoskeletons retained cell‐like shapes for at least 2 h, but at higher pH values, they lost stability after 30 min, appearing as amorphous protein material. Irradiation in the presence of1–20 μM protoporphyrin‐IX at pH 6.5 caused crosslinking of the proteins when organized as cytoskeletons, but not when separated. Scanning electron microscopy also revealed that the cytoskeletal proteins conserved their cell‐like shape even at pH values higher than 7.0. It was concluded that illumination in the presence of porphyrin causes membrane rigidity by crosslinking of the cytoskeletal proteins, and their sensitivity to crosslinking is the result of their mutual arrangement in the membrane. At concentrations higher than 100 μM protoporphyrin‐IX induced, even in the absence of light, the opposite effect, namely dissociation of the cytoskeletal proteins. The data suggest that the changes observed in this study provide an explanation for both dark and light induced injuries of red cells in porphyria disorders.