Effect of endotoxin-induced monokines on glucose metabolism in the muscle cell line L6.

Abstract

Exposure of fully differentiated L6 myotubes to a crude monokine preparation from endotoxin-stimulated RAW 264.7 cells resulted in a rapid and substantial (70%) increase in fructose 2,6-bisphosphate concentration coincident with a depletion of cellular glycogen and an increased lactate production. During the time required for glycogen depletion (3 hr), stimulation of 3-O-methyl-D-glucose and 2-deoxy-D-glucose uptake was initiated and observed to reach a maximum enhancement of 200% 12-15 hr later. The monokine had no effect on the Km value for 2-deoxy-D-glucose uptake (1.1 mM), while Vmax was increased from 912 to 2400 pmol/min per mg of protein. The increase was cytochalasin B inhibitable and was dependent on protein synthesis. Photoaffinity labeling and equilibrium binding studies with [3H]cytochalasin B support the hypothesis that this increase in hexose transport was due to an increase in hexose transporters present in the plasma membrane. Purified recombinant interleukin-1 alpha had no effect on hexose transport, whereas purified recombinant cachetin/tumor necrosis factor did stimulate hexose uptake, with half-maximal stimulation occurring at 36 nM. Although cachetin accounts for most of the biological activity associated with the crude monokine preparations, it is not the only monokine capable of inducing glucose transport in L6 cells. Specific immunoabsorption of cachectin/tumor necrosis factor from the crude monokine preparation revealed a monokine that had a similar bioactivity at extremely low concentrations on L6 cells.