Endosomes: another extra-mitochondrial location of type-1 porin/voltage-dependent anion-selective channels.

Endocytotic vesicles (EV) isolated from rat renal cortex were subjected to SDS-polyacrylamide gel electrophoresis and Western blotting. A monoclonal antibody against human type-1 porin (31 kDa) detected a strong band of 31 kDa. The same antibody has been used as the primary antibody in indirect immunocytochemistry. Light microscopy of cryostat sections of rat renal cortex showed a heavy staining of EV underneath the brush-border membrane. Electron microscopy was performed by "preembedding immunogold staining" of rat renal cortex, the sections of which showed an extensive labelling of EV with gold particles. These results demonstrate that the expression of type-1 porin is not restricted to outer mitochondrial membranes. The biological function of endosomal type-1 porin has as yet to be ascertained.