PHOSPHATIDYLGLYCEROL (PG) STIMULATES SYNTHESIS OF PHOSPHATIDYLCHOLINE (PC) IN CULTURED TYPE II PNEUMOCYTES

We examined the effect of exogenous phospholipid (PL) on PL synthesis in type II cells. Cells isolated from adult rats were cultured for 18-20 h in medium containing fetal bovine serum and antibiotics. After washing, the cells were further incubated for 1-6 h in serum free medium containing PL - dispersed by sonicationand radiolabeled precursor. PL increased the rate of choline incorporation into PC. PG and cardiolipin stimulated the most but phosphatidic acid, phosphatidylethanolamine (PE), phosphatidylinositol and phosphatidylserine - but not PC or sphingomyelin - were also stimulatory. The effect of PG was concentration dependent in the range 10-9 to 10-4M and was apparent at all times examined. Incubation with 10-5M PG for 2 h increased the rate of [3H]choline incorporation into PC by 72% from 5200±700 (mean ± SE, n=7) cpm/106 cells (no PG) to 8600±900 (P<0.001, paired t test). Similarly, PG increased the rate of [3H]glycerol incorporation into PC by 50% from 720±100 cpm/106 cells to 1080±140 (P<0.002, n=6). The effect was specifically on PC; rates of glycerol incorporation into other PL or of [14C]ethanolamine into PE were not increased. It is unlikely that the effect of PG is due to increased substrate as it was not mimicked by glycerol, glycerophosphate or palmitate. Neither does it appear to be due to enhanced cell growth: rates of [14C]leucine and [3H]thymidine incorporation into protein and DNA, respectively, were not increased. The relevance, if any, of these findings to surfactant turnover and reutilization remains to be elucidated. (Supported by HD-10192.)