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 (VO2) 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 PO2 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 VO2 as cell density increased, and SMC VO2 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 microg/ml) caused a decrease in VO2 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 VO2 to normal values after exposure to LPS. These data suggest that endotoxin impairs VO2 in cells derived from the vascular wall and indicate the importance of EC and SMC respiration in maintaining vascular homeostasis under conditions of sepsis.