Mobile lipid production after confluence and pH stress in perfused C6 cells

NMR‐visible mobile lipid (ML) has been observed in aggressive tumors and also in in vitro tumor cell models subjected to growth‐inhibiting conditions, such as confluence or low‐pH stress. The aim of the present study was to determine if ML production after confluence or low pH stress in a cultured cell model of brain tumor is due to growth arrest alone. ML was observed in situ by one‐ and two‐dimensional 1H NMR in viable but growth‐arrested C6 glioma cells superfused for a period of 48 h after harvesting. The rate of ML production in cells harvested at subconfluence was compared to the rate in cells confluent for one cell cycle and to the rate in subconfluent‐harvested cells superfused at low pH (pH 6.1). Confluent‐harvested cells produced ML at a markedly greater rate than that of cells harvested at subconfluence, suggesting the involvement of prior cell–cell contact rather than simple growth arrest. A high rate was also observed in subconfluent‐harvested cells subjected to low pH, indicating that ML in pH‐stressed cells also does not arise from growth arrest alone. Furthermore, two‐dimensional data on the degree of unsaturation of the ML fatty acyl chains and one‐dimensional 31P and two‐dimensional 1H NMR data on the GPC content of the cells suggest distinct metabolic pathways for the production of ML following confluence and low‐pH stress. Copyright © 2001 John Wiley & Sons, Ltd. Abbreviations used: ACSF artificial cerebrospinal fluid GPC glycerophosphocholine ICr initial creatine ML NMR‐visible mobile lipid PCr phosphocreatine PLA1 phospholipase A1 PLA2 phospholipase A2 TG triacylglycerol.