Glucocorticoid Effects on Lipid Lateral Diffusion and Membrane Composition in Lipopolysaccharide-activated B-Cell Leukemia 1 Cells1

We have investigated the effects of glucocorticoid treatment on lipid lateral diffusion and cholesterokphospholipid ratios in the plasma mem branes of the lipopolysaccharide (LPS)-responsive murine B-cell leuke mia (BCL,). Exposure to LPS for 24 h at concentrations of 50 ¿tg/ml, 100 Mg/ml, and 250 Mg/ml caused a 42% reduction in the lateral diffusion of the lipid probe 3,3'-dioctadecylindocarbocyanine iodide as measured by fluorescence photobleaching recovery techniques at 37°C. In cells incubated with 50 Mg/ml LPS, 3,3'-dioctadecylindocarbocyanine iodide diffusion is reduced to 2.2 x 10 '' uu2s ' compared to freshly isolated BCLi cells where 3,3/-dioctadecylindocarbocyanine iodide diffused at a rate of 3.8 x 10"* cm V. In BCL, cells activated by LPS for 24 h and recultured with a pharmacological concentration of the synthetic gluco corticoid triamcinolone acetonide (TA, III"'' M) for 6 h, lipid lateral diffusion increased to 3.5 x IO"9 cmV. Concentrations of TA lower than 10 '' M had no effect on lipid lateral diffusion. Six-h treatment with 10~* M TA had no effect on freshly isolated BCL, cells (Time 0). However, lipid lateral diffusion increased in cells incubated 24, 48, and 72 h with LPS, and an additional 6 h with 10~* M TA suggested that activated BCL, cells were more glucocorticoid sensitive than cells at Time 0. Plasma membrane cholesterol and phospholipid content, analyzed at 0 and 24 h, indicated that LPS activation was associated with a 7% increase in the cholesterokphospholipid ratio in BCL, membranes and that glu cocorticoid treatment of these LPS-activated cells for 6 h decreased the membrane cholesterol:phospholipid ratio perhaps through inhibition of tie novo cholesterol synthesis.