Multiple effects of amobarbital on Ehrlich ascites tumor cells. Inhibition of pyruvate dehydrogenase.

The inhibition of the proliferation of hyperdiploid Ehrlich ascites tumor cells in suspension cultures by amobarbital is coupled to an increased glycolytic activity as shown by lactic acid production and glucose consumption; higher concentrations of amobarbital than 1 mM enhance the ATP/ADP ratio of the total cell. The actual activity of pyruvate dehydrogenase of intact cells is completely inhibited in the presence of 2 mM amobarbital as was shown by the 14CO2 evolution from [114C]pyruvate or the incorporation of 14CO2 into the total lipid fraction of the cells from [U-14C]lactate. The pyruvate dehydrogenase complex from Ehrlich ascites tumor cells is completely inhibited by 1 mM amobarbital in vitro. The activity of alpha-oxoglutarate dehydrogenase is inhibited by amobarbital, too, as well as shown by measuring the 14CO2 evolution from [1-14C]glutamate with intact cells. It is suggested that the inhibition of pyruvate dehydrogenase in the presence of amobarbital is the result of a direct action on the enzyme as well as the consequence of a change in the cellular redox state or its energy charge.