Structural modifications of the permeability transition pore complex in resealed mitochondria induced by matrix-entrapped disaccharides

Mitochondrial resealing after the opening of the permeability transition (PT) pore was studied in saline and sugar-based media by following the fluorescence anisotropy changes of mitochondria-bound hematoporphyrin (HP), a probe sensitive to conformational variations of the pore complex (Ricchelli et al., 1999, Biochemistry 38, 9295-9300). The HP-anisotropy changes correlated well with complete mitochondrial resealing in saline media and suggested that the pore complex regained the native structure after closure. Rebuilt up of the pore complex structure was also achieved in monosaccharide-based media thus ruling out a major influence of the swollen state of mitochondria on the reconstitution properties of the pore components. On the contrary, when sucrose or other disaccharides were used as osmotic support, restoration of the native mitochondrial structure, as monitored by HP-anisotropy, was not achieved, though the proton barrier of the inner membrane as well as respiration functions were reestablished. Infrared spectroscopy experiments indicated the occurrence of strong perturbations of the mitochondrial membrane structure after disaccharide entrapment in the matrix space. These data suggest that mitochondria are able to reseal and regain the functional activity after opening of the PT pore irrespective of the incubation medium but in sucrose (and other disaccharides) the pore complex adopts a conformation different from that existing before permeabilization. In general, our data indicate that the pore complex can exist in different conformations which are modulated by the nature of the interactions with the medium cosolvents.