Stimulation of phospholipid metabolism in embryonic muscle cells treated with phospholipase C.

Phospholipid metabolism is dramatically stimulated in cultured myogenic cells in which cell fusion was inhibited with phospholipase C (phosphatidylcholine choline-phosphohydrolase; EC 3.1.4.3). Phospholipase C was active under the culture conditions as shown by the degradation of exogenous phosphatidylcholine. Rates of incorporation of 32Pi and [methyl-3H]choline into lipids were about 5-fold greater in phospholipase-treated cells than in either untreated fusing cells or untreated cells prevented from fusing by calcium deprivation. The greatest stimulation in the phospholipase C-treated cultures occurred with synthesis of phosphatidylcholine and sphingomyelin; synthesis of phosphatidylinositol and cardiolipin was not stimulated. Degradation of cellular [32P]phosphatidylcholine and appearance in the culture medium of the degradation product [32P]phosphocholine were both increased. Levels of total cellular phospholipids and of individual phospholipid classes were similar in control and phospholipase-treated cells. The results suggest that the membrane phospholipid composition in myogenic cells is controlled by a regulatory mechanism which increases the synthesis of phospholipids that are degraded in the presence of the phospholipase.