Evidence that Bacitracin Alters Intracellular Insulin Metabolism in Isolated Rat Hepatocytes

The effect of bacitracin on intracellular insulin degradation was investigated using an isolated rat hepatocyte preparation In which essentially all insulin degradation was due to cell-mediated processes. Bacitracin produced a concentration-dependent decrease in the degradation of insulin to products soluble in trichloroacetic acid, with a half-maximal effect at approximately 0.5 mM. These results were confirmed by analysis of extracted cell-bound radioactivity by Sephadex G-50 molecular sieve chromatography. Radioactive material eluting in the position of intact insulin from the G-50 column was further analyzed by reversed-phase, highperformance liquid chromatography. In addition to intact insulin, two peaks of radioactive material less hydrophobic than insulin were evident. Incubation of cells in the presence of 0.5 mM bacitracin significantly (P < 0.05) altered the distribution of radioactivity in these two peaks. These results indicate that bacitracin significantly affects hepatocyte insulin metabolism and suggest that the continued use of bacitracin in studies of hepatocyte-insulin interaction should be avoided.