Uncoupler stimulated adenosine triphosphatase activity. Deficiency in intact mitochondria from Morris hepatomas and ascites tumor cells

Well coupled mitochondria isolated from 6 hepatomas differing widely in growth rate and degree of differentiation were found to exhibit little or no 2,4 dinitrophenol stimulated ATPase activity in sharp contrast to normal liver mitochondria. Well coupled mitochondria from L1210 and Ehrlich ascites tumor cells were also found to have markedly reduced uncoupler stimulated ATPase activity when compared with normal liver mitochondria. When intact mitochondria from one of the hepatomas (7800) were studied in greater detail, it was found that normal uncoupler dependent ATPase activity could not be demonstrated under a variety of conditions. These included the use of uncouplers more potent than 2,4 dinitrophenol; alteration of osmotic and ionic conditions; variation of temperature between 20 and 40°; variation of pH between 6.9 and 9.5; and inclusion of either defatted bovine albumin or oxidizable substrate in the assay medium. Neither forward nor reverse energy dependent reactions in hepatoma 7800 mitochondria are altered, nor is their sensitivity to uncoupling agents. In the forward direction, hepatoma mitochondria were found to exhibit normal acceptor control and P:O ratios sensitive to uncouplers, and to exhibit uncoupler stimulated respiration. In the reverse direction, the ATP/P(i) exchange rate was found to be the same in hepatoma 7800 and control liver mitochondria and inhibited almost completely in both cases by 2,4 dinitrophenol. In addition, the capacity for ATP supported Ca²⁺ accumulation was similar for hepatoma 7800 and control liver mitochondria. Unlike hepatoma mitochondria, mitochondria isolated from regenerating liver 24, 48, and 72 hr after partial hepatectomy exhibit normal levels of uncoupler stimulated ATPase activity. These results are interpreted most simply by assuming that hepatoma mitochondria, and perhaps mitochondria from L1210 and Ehrlich ascites tumor cells, contain two principal sites of action for uncoupling agents, one of which may become expressed during the normal to neoplastic transition.