Depression of endothelial and smooth muscle cell oxygen consumption by endotoxin

An optical method based on the oxygen-dependent quenching of a phosphorescent probe (palladium-porphyrin) was used to investigate the effect of bacterial endotoxin [lipopolysaccharide (LPS)] on oxygen consumption (V) over dot O-2 by vascular cells. Endothelial (EC) and smooth muscle (SMC) cells from pig aorta were suspended in culture medium in the presence of palladium-porphyrin and transferred to glass capillary tubes that were sealed to create a hypoxic environment. Measured Po, changed as a function of time in a highly predictable fashion when cell suspensions were exposed to agents or treatment known to affect cellular metabolism. Both EC and SMC showed a significant decrease in (V) over dot O-2 as cell density increased, and SMC (V) over dot O-2 was significantly higher than EC (1.94 +/- 0.09 vs. 1.0 +/- 0.15 nmol.min(-1).10(6) cells(-1)). Exposure to LPS (1 mu g/ml) caused a decrease in (V) over dot O-2 of 46% and 15% for EC and SMC, respectively. Pretreatment of cells with N-acetyl-L-cysteine, a substrate for glutathione synthesis with antioxidant properties, restored (V) over dot O-2 to normal values after exposure to LPS. These data suggest that endotoxin impairs (V) over dot O-2 in cells derived from the vascular wall and indicate the importance of EC and SMC respiration in maintaining vascular homeostasis under conditions of sepsis.