Early cellular responses in vitro to endotoxin administration.

The sequence of early events which follow the administration of E coli lipopolysaccharide (LPS) to cultured mouse neuroblastoma (C-1300) cells was investigated. Emphasis was placed on cellular energy metabolism in order to establish whether or not an energy failure occurred and whether it was a primary or a secondary effect. Exposure of cultured neuroblastoma cells to LPS produced rapid changes in the regulatory parameters of energy metabolism, an oxidation of intramitochondrial pyridine nucleotides, and a decline in cellular [ATP]/[ADP] [Pi], which were followed by alterations in mitochondrial morphology. In spite of the changes in individual parameters at early stages of exposure to LPS, the cellular energy producing systems remained tightly controlled and the rate of ATP synthesis was maintained at a constant and undiminished level. This allowed the cells to preserve their ionic gradients as manifested by high intracellular [K+] and unaltered transmembrane electrical and pH gradients. These early changes in mitochondrial metabolism were not accompanied by detectable leakage of mitochondrial matrix enzymes into the cytosol, which indicated that mitochondrial membrane remained intact. After longer exposure to LPS, the rate of ATP synthesis declined, the mitochondrial membrane became permeable to high molecular weight substances (matrix enzymes), and intracellular [K+] began to decrease (K+ leakage). It was concluded that responses of mitochondrial metabolism are one of the early events in endotoxemia.