A Circulating Factor(s) Mediates Cell Depolarization in Hemorrhagic Shock

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Abstract
Cell depolarization in hemorrhagic shock has been attributed to hypoperfusion, but the mechanism remains unclear. Suspensions of single cell lines loaded with the potential-sensitive fluorescent dye bis-(1,3-dibutylbarbiturioc acid) trimethine oxonal (DIBAC) and exposed for 30 minutes to rat plasma drawn either before or after hemorrhagic shock (bled 20 mL/kg: mean arterial blood pressure less than 40 mmHg) were studied. Plasma drawn after, but not before, hemorrhage led to partial depolarization regardless of cell type (rat H9C2 skeletal muscle, A-10 smooth muscle, C-9 liver, adrenal, kidney, red blood cell [RBC], white blood cell [WBC]) or species (cat, dog, pig RBC; cat WBC; mouse C2C12 skeletal muscle; and human intestinal smooth muscle [HISM]). Dialysis did not remove the factor(s), suggesting a molecular weight of more than 10,000 daltons. The factor appeared within 5 minutes of shock. The depolarization amplitude increased as a function of plasma concentration and demonstrated saturation kinetics indicating specific receptor binding. Cells were equivalently oxygenated, excluding hypoperfusion as a necessary condition for depolarization. Tumor necrosis factor or platelet activating factor alone or in combination were not effective in this system. Stable measurements can be obtained with this noninvasive system that avoids cell injury consequent to cell impalement with electrodes. This system provides a sensitive in vitro bioassay that should permit identification of the plasma factors mediating cell depolarization, as well as definition of the responsible intracellular mechanisms.