CHOLINE INCORPORATION INTO PHOSPHOLIPIDS IN MESOTHELIAL CELLS IN-VITRO

Objective: To determine the effect of extracellular choline concentrat ion on phospholipid production and handling by peritoneal mesothelial cells in vitro. Design and measurements: Radiolabeled choline was used td monitor the formation of phosphatidylcholine (PC), sphingomyelin ( SPH), and lysophosphatidylcholine (LPC) by rat and rabbit mesothelial cells as a function of concentration and time of exposure to choline. The subcellular location of the newly formed phospholipids was examine d hy ultracentrifugation in Percoll-sucrose gradients using analytical cell fractionation techniques. The fatty acid composition of the PC f ormed was determ ined by thin- layer chromatography (TLC) and gas chro matography. Results: Choline incorporation into PC, SPH, and LPC incre ased with extracellular choline levels up to 640 mu mol/L, which is 10 0 times greater than physiological levels of choline in plasma and 20 times higher than choline levels measured in peritoneal dialysis efflu ent. The newly formed, radiolabeled phospholipids were primarily found in a single subcellular compartment that exhibited a buoyant density of 1.05 g/mL in Percollsucrose gradients. Analysis of the fatty acyl g roups of PC obtained from the mesothelial cells showed enrichment in p almitic [16:0], oleic [18:1], and linoleic [18:2] acids. Conclusion: T he rate of phospholipid formation by mesothelial cells in vitro can be manipulated, in part, by choline concentration.