VALINOMYCIN INDUCES APOPTOSIS OF ASCITES HEPATOMA-CELLS (AH-130) IN RELATION TO MITOCHONDRIAL-MEMBRANE POTENTIAL

Valinomycin is a potassium ionophore, and is well known to cause the c ollapse of the mitochondrial membrane potential. It has been reported that loss of mitochondrial membrane potential is observed in the early stages of apoptosis induced by various agents. Thus, the effects of v alinomycin on tumor cells were examined. Valinomycin induced uncouplin g of respiration and depolarization of isolated mitochondria. Depolari zation of intact mitochondria in AH-130 rat ascites hepatoma cells was also induced by valinomycin. Valinomycin induced apoptosis revealing the typical apoptotic characteristics such as fragmentation and ladder formation of DNA, shrinkage of cells, and formation of pycnotic nucle us. There was a correlation between the depolarization of mitochondria and DNA fragmentation. After depolarization of mitochondria, the acti vity of caspase-3-like protease but not caspase-1-like protease increa sed markedly. In contrast, this apoptosis did not involve the release of reactive oxygen species from mitochondria, increase in intracellula r calcium concentration, or protein synthesis. In addition, anti-apopt otic members of the Bcl-2 family (Bcl-2 and Bcl-2) were not correlated with apoptosis. These results indicate that valinomycin might induce apoptosis through degradation of the mitochondrial membrane potential. Taken together, these observations suggest that there may be a mechan ism that transmits the signal from mitochondrial depolarization to sub sequent apoptosis execution steps.