Choline Incorporation into Phospholipids in Mesothelial Cells in Vitro

Objective To determine the effect of extracellular choline concentration on phospholipid production and handling by peritoneal mesothelial cells in vitro.Design and Measurements Radiolabeled choline was used to monitor the formation of phosphatidylcholine {PC), sphingomyelin (SPH), and Iysophosphatidylcholine (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 examined by ultracentrifugation in Percoll-sucrose gradients using analytical cell fractionation techniques. The fatty acid composition of the PC formed was determined by thin-layer chromatography (TLC) and gas chromatography.Results Choline incorporation into PC, SPH, and LPC increased with extracellular choline levels up to 640 μmol/L, which is 100 times greater than physiological levels of choline in plasma and 20 times higher than choline levels measured in peritoneal dialysis effluent. 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 groups of PC obtained from the mesothelial cells showed enrichment in palmitic [16:0], oleic [18:1], and linoleic [18:2] acids.Conclusion The rate of phospholipid formation by mesothelial cells in vitro can be manipulated, in part, by choline concentration.