A circulating shock protein depolarizes cells in hemorrhage and sepsis

Objective: A study to determine if both septic and hemorrhagic shock lead to the appearance of a substance that depolarizes cells in plasma was performed. Summary Background Data: Transmembrane potential decreases in skeletal muscle, hepatocytes, and red blood cells early in the development of both hemorrhagic and septic shock. The associated movement of ions and water into cells leads to extracellular fluid loss and exacerbates shock. Methods: Adult male Sprague-Dawley rats with indwelling arterial and venous cannulae were bled 20 mL/kg or received intravenously 2 x 10¹⁰ Escherichia coli suspended in 400 mL of 0.9% saline. Blood samples were taken after hemorrhage and induction of sepsis to determine the presence of a plasma factor that depolarized red blood cells. Control rats were not injected with E. coli or bled. Plasma from bled and septic rats was processed by sequential precipitation with ammonium sulfate and subjected to gel filtration. Results: Depolarizing activity was highest 20 minutes after hemorrhage and 60 minutes after E. coli injection, decreasing to control levels by 2 (hemorrhage) and 4 (sepsis) hours. Control rats showed no significant change in depolarizing activity. Tryptic and chymotryptic digestion eliminated the depolarizing activity, indicating that the active substance is, at least in part, a protein. Depolarizing activity from bled and septic processed plasma was confined essentially to the 70% ammonium sulfate fraction and the activity migrated with an apparent molecular mass of 200 kD after gel filtration. Separation of the complex by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) produced an identical pattern of bands in both bled and septic animals. Conclusions: A circulating plasma protein complex of high molecular weight causes cellular depolarization in both hemorrhage and sepsis and may be responsible for the associated increases in cell sodium and water seen in both hemorrhagic and septic shock.