Ferric iron potentiates cell depolarization by a circulating shock protein

B. J. Eastridge, J. A. Evans, D. N. Darlington and D. S. Gann
Department of Surgery, University of Maryland School of Medicine, Baltimore.

OBJECTIVE: To determine whether or nor iron affects the depolarizing activity of a circulating shock protein that appears in plasma after hemorrhage. DESIGN: Randomized design. SETTING: University laboratory. ANIMALS: Healthy male Sprague-Dawley rats weighing 300 to 400 g with femoral artery and vein cannulas placed 4 days before hemorrhage. INTERVENTION: A 20-mL/kg hemorrhage and plasma collection. MAIN OUTCOME MEASURES: Depolarizing activity was measured as the increased fluorescence of an oxonol dye in the presence of Fe3+, Fe2+, or the iron chelator deferoxamine mesylate and was titrated against increasing concentrations of circulating shock protein or iron. Circulating shock protein was derived from plasma and was purified in two steps: stepwise ammonium sulfate precipitation followed by denaturing ion-exchange chromatography and refolding. RESULTS: At physiologic concentrations, Fe3+ but not Fe2+ potentiated the depolarizing activity of plasma after ammonium sulfate. Addition of deferoxamine abolished activity. Denaturing chromatography removed nearly all the depolarizing activity; however, Fe3+ restored activity to this fraction. Fe3+ increased total activity and decreased the concentration at which 50% activity was observed. CONCLUSION: These data indicate that physiologic concentrations of Fe3+ may act to modulate the depolarizing activity of circulating shock protein that in turn mediates the intracellular accumulation of salt and water in shock.