Cellular Effects of Endotoxin in Vitro: Mobility of Endotoxin in the Plasma Membrane of Hepatocytes and Neuroblastoma Cells
PENNSYLVANIA UNIV PHILADELPHIA
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Little is known about the mechanism of action of endotoxins at the cellular level, although their effects in clinical situation sand experimental animals have been characterized extensively. Previous studies from this laboratory 1-3 have used isolated cells as an in vitro model system and explored early cellular responses changes in metabolites, ion contents and enzyme activities to endotoxin exposure. In the present work, we have used fluorescein isothiocyanate labeled lipopolysaccharide to examine directly the mechanism of toxin attachment to mammalian cell membranes. Earlier investigations have shown that endotoxins have the ability to bind to and interact with almost all types of mammalian cells 4-9. Whether this interaction occurs through nonspecific lipid-lipid contacts, which cause membrane destabilization andor changes in fluidity, or through binding to a specific membrane component, which initiates cellular perturbations, remains to be determined. The results suggest that endotoxin binding to mammalian cells consists of two subpopulations with different mobilities binding of the immobile fraction is dependent on cellular integrity and the differences in binding, lateral mobility, and size of the immobile fraction in hepatocytes and neuroblastoma cells may be due to variations in membrane composition andor number of binding sites.