Mitochondrial permeability transition and swelling can occur reversibly without inducing cell death in intact human cells

Severe disruption of mitochondrial function is generally considered to provide a powerful trigger for apoptosis in mammalian cells. We report here that intact cells may undergo the mitochondrial permeability transition and mitochondria swell in a fully reversible manner, without inducing cell death. Cultured human osteosarcoma cells (143B TK-) stained with JC-1, MitoTracker dyes, or calcein plus Co2+ were imaged by confocal microscopy to visualize changes of mitochondrial membrane potential (Delta Psi(m)), morphology, and permeability transition, respectively, during treatment with a protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), Cells rapidly exhibited mitochondrial permeability transition and swelling after addition of CCCP, but the swelling subsided within hours, leaving mitochondria that appeared in punctate form, not filamentous as before CCCP treatment. Cyclosporin A impeded the permeability transition and swelling, although complete inhibition was not observed. Cells survived the dissipation of Delta Psi(m) by CCCP for up to 6 h without developing any obvious cell damage or signs of apoptosis. With the restoration of Delta Psi(m) after removal of CCCP (following 6 h of CCCP treatment), permeability transition pores were closed. These results suggest that none of the following events represent a point of no return in the process of apoptotic cell death: loss of Delta Psi(m) mitochondrial permeability transition, or mitochondrial swelling, (C) 1999 Academic Press.