Photodynamic effects of protoporphyrin on red blood cell deformability

Summary Human erythrocytes exposed to visible light in the presence of protoporphyrin showed a pronounced decrease of cell deformability. The photodynamic action of protoporphyrin on red blood cells has previously been shown to cause a.o. an extensive cross-linking of spectrin. As spectrin is presumably involved in processes regulating cell shape and viscoelasticity, conceivably the decreased deformability is attributable to the cross-linking of this protein. Iodosobenzoate evoked a similar decreased cell deformability, due to the formation of disulphide bridges by this agent. These S-S linkages could be reduced by dithiothreitol, with a concomitant change of cell deformability to normal values. Dithiothreitol had only a very limited effect on the protoporphyrin-sensitized decrease of cell deformability and protein cross-linking, indicating that the photodynamic effects cannot be rationalized on the basis of disulphide formation.