Effect of E coli endotoxin on the leakage of 14C-sucrose from phosphatidylcholine liposomes.

The effect of E coli endotoxin on the leakage of 14C-sucrose from phosphatidylcholine liposomes in the absence or presence of Ca2+ was studied. Endotoxin decreased the leakage from liposomes from 27% to 4% in 5 hr when Ca2+ (1 mM) was incorporated into liposomes during sonication. The effect of endotoxin on the leakiness of liposomes was concentration dependent. Ca2+ alone increased the leakage of 14C-sucrose from liposomes. Mg2+ at concentrations higher than 5 mM exhibited an effect similar to that of Ca2+. These findings suggest that endotoxin increases the molecular packing of phosphatidylcholine bilayers in the presence of Ca2+ or Mg2+. A change in the physical state of membrane lipid bilayers induced by endotoxin may affect the function of biological membranes.