Nitric oxide synthase inhibition negates septic-induced alterations in cytoplasmic calcium homeostasis and membrane dynamics.

This study was undertaken to evaluate the role of nitric oxide (NO) in the sepsis-induced disruption of intracellular calcium homeostasis and membrane dynamics. Anticoagulated whole blood was obtained from 10 healthy volunteers. Equal aliquots were incubated with saline (control), 2 microg/mL Escherichia coli endotoxin (lipopolysaccharide), 8 microg/mL NO inhibitor, N-monomethyl arginine (NMA), and endotoxin plus NO inhibitor (lipopolysaccharide/NMA). Erythrocytes were harvested, washed, and loaded with the calcium chelator, FURA-2AM, and the fluorescent membrane probe TMA-DPH. Cells were evaluated for both intracellular calcium concentration and membrane viscosity (anisotropy) by fluorescent spectrophotometry. Endotoxin induced a significant increase in both intracellular calcium concentration and anisotropy. NMA had no intrinsic affect on either of these cellular characteristics. NMA was, however, effective in preventing the endotoxin-induced changes. These results suggest that NO may play a role in the disruption of intracellular calcium homeostasis and erythrocyte membrane deformability noted in sepsis.