Carbon tetrachloride inhibits synthesis of pulmonary surfactant disaturated phosphatidylcholines and ATP production in alveolar type II cells

Abstract

Other studies have shown that inhalation of carbon tetrachloride (CCl4) decreases the amount of pulmonary surfactant lining the alveolar surface. Therefore, we studied the effects of CCl4 on the synthesis of surfactant phosphatidylcholines (PCs) in rat alveolar type II cells in vitro. The rate of incorporation of choline, palmitate or glycerol into disaturated PC (DSPC) is decreased in a concentration-dependent manner. The CCl4 concentrations which cause maximal inhibition and 50% inhibition are similar for each substrate. The rate of incorporation of choline or glycerol into total PC is diminished to the same extent as their incorporation into DSPC. In addition, the rate of incorporation of glycerol into phosphatidylglycerol is decreased by the same extent as its incorporation into PC. All of these data suggest that there is a common site(s) at which CCl4 inhibits PC synthesis and that the inhibition occurs early in the biosynthetic pathway. However, individual enzymes involved in phospholipid synthesis do not seem to be affected by the solvent. Exposure of alveolar type II cells to CCl4 does cause a rapid and dramatic loss in cellular ATP, a cofactor required by some enzymes involved in PC synthesis. Studies with isolated lung mitochondria suggest that CCl4 inhibits the enzyme complex which catalyzes the synthesis of ATP from ADP. In addition, CCl4 causes a decrease in the amount of 3-O-methylglucose associated with type II cells, suggesting that glucose influx is impaired. This may also contribute to lower cellular ATP levels. The results of this study suggest that inhalation of CCl4 may impair surfactant phospholipid synthesis by decreasing ATP levels in alveolar type II cells.