Mitochondrial DNA (mtDNA) mutations have been found associated with several neuromuscular diseases. In order to address further mechanisms of pathogenesis of the specific mtDNA mutations in responsible for these diseases, the ρ° human cell culture system has been established and has been widely used in recent years (4)'(5). This system is based upon the repopulating of human cells, which are completely depleted of mtDNA (termed ρ° cells), with exogenous mitochondria containing the mtDNA of interest. Molecular genetic and biochemical analysis showed that transformants can be obtained with various mitochondrial donors and the respiratory competence can be restored. In this study, the ultrastructural and immunocytochemical variations of mitochondria in human cell lines cultured in this system observed by transmission electron microscopy are reported.

Cell cultures for wild-type 143B, ρ206, and transmitochondrial cell lines have been described previously. Cells were trypsinized and collected from individual culture plates, and then were fixed with 3% paraformaldehyde and 0.04% glutaradehyde in 0.1 M phosphate-buffered saline (PBS) with 4% sucrose (pH 7.6) at RT.