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 prov ide a powerful trigger for apoptosis in mammalian cells. We report here tha t intact cells may undergo the mitochondrial permeability transition and mi tochondria swell in a fully reversible manner, without inducing cell death. Cultured human osteosarcoma cells (143B TK-) stained with JC-1, MitoTracke r dyes, or calcein plus Co2+ were imaged by confocal microscopy to visualiz e changes of mitochondrial membrane potential (Delta Psi(m)), morphology, a nd permeability transition, respectively, during treatment with a protonoph ore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), Cells rapidly exhibit ed mitochondrial permeability transition and swelling after addition of CCC P, but the swelling subsided within hours, leaving mitochondria that appear ed in punctate form, not filamentous as before CCCP treatment. Cyclosporin A impeded the permeability transition and swelling, although complete inhib ition was not observed. Cells survived the dissipation of Delta Psi(m) by C CCP for up to 6 h without developing any obvious cell damage or signs of ap optosis. With the restoration of Delta Psi(m) after removal of CCCP (follow ing 6 h of CCCP treatment), permeability transition pores were closed. Thes e 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) mitoch ondrial permeability transition, or mitochondrial swelling, (C) 1999 Academ ic Press.