Evidence that the rate of phosphatidylcholine catabolism is regulated in cultured rat hepatocytes

Abstract

The regulation of phosphatidylcholine (PC) catabolism has been studied in choline-deficient rat hepatocytes. Supplementation of choline-deficient hepatocytes, prelabeled with [ 3H]choline, with 100 μM choline increased the rate of PC catabolism by approx. 2-fold. The major product of PC degradation was glycerophosphocholine in both choline-deficient and choline-supplemented cells. Choline supplementation decreased the radioactivity recovered in lysoPC by 50%. This effect was accompanied by a 2-fold increase of labeled glycerophosphocholine. Comparable results were obtained when PC of the cells was prelabeled with [ 3H]methionine or [ 3H]glycerol. The activity of phospholipase A in cytosol, mitochondria and microsomes isolated from choline-deficient rat liver was similar to the activity in control liver, when determined with [ 3H]PC vesicles as the substrate. Measurement of the activity of phospholipase A with endogenously [ 3H]choline-labeled PC showed that the formation of lysoPC in mitochondria isolated from choline-supplemented cells was 40% lower than in choline-deficient cells. Alternatively, the formation of [ 3H]glycerophosphocholine and [ 3H]choline in microsomes from choline-supplemented cells was significantly higher (1.4-fold) than in microsomes from choline-deficient cells. These results suggest that the rate of PC catabolism is regulated in rat hepatocytes and that the concentration of PC might be an important regulatory factor.