We studied mitochondria of digitonin-permeabilized HeLa cells, since digitonin (60 micrograms/10(6) cells) increases plasma membrane Ca2+ permeability, in order to avoid problems such as low mitochondrial yield and the possibility of obtaining damaged or uncoupled mitochondria from tumor cells. 2. Addition of Ca2+ to digitonin-permeabilized HeLa cells gave rise to a cycle of respiratory stimulation. Ca2+ uptake was almost totally inhibited by antimycin A (6.0 micrograms/ml). 3. Ca2+ release occurred upon addition of carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) to digitonin-permeabilized HeLa cells, under steady-state conditions. An antimycin A- and FCCP-insensitive Ca2+ uptake was also detected in this preparation when ATP was added, which reflects Ca2+ capture by other organelles. 4. The characteristics of the mitochondrial Ca2+ transport system in HeLa cells are similar to those of other previously studied tumor cells. Mitochondria from HeLa cells are resistant to the deleterious effects of massive Ca2+ loads.
