Superoxide radical scavenging prevents cellular calcium dysregulation during intraabdominal sepsis

The role of superoxide in sepsis-altered hepatocyte Ca2+i regulation was studied by examining the effect of treatment of septic rats with superoxide dismutase-polyethylene glycol (SOD-PEG) on hepatocyte Ca2+ influx and efflux, and cytosolic [Ca2+]. Rats were implanted with sterile or bacteria-laden (Escherichia coli and Bacteroides fragilis) fecal pellets into the abdominal cavity. Eight hours after the implantation, rats were treated with SOD-PEG or its vehicle PEG. Septic and sterile implanted rats were killed 24 h postimplantation, and their livers were removed to isolate viable hepatocytes. Isolated hepatocytes were incubated with traces of 45Ca to assess Ca2+ influx and efflux. The 45Ca exchange assessments also allowed calculation of the intracellular exchangeable Ca2+ contents. [Ca2+]i was quantified by the use of fluorescent dye indo-1 and microfluorometric techniques. There were no differences in the Ca2+ influx, Ca2+ efflux, intracellular exchangeable Ca2+, or [Ca2+]i between the treated or untreated sterile and unoperated controls. However, compared with the nonseptic groups, the septic rats with or without administration of the vehicle (PEG) showed marked increases in Ca2+ influx, intracellular exchangeable Ca2+ and [Ca2+]i but not Ca2+ efflux. When challenged with vasopressin, the hepatocytes from septic rats, administered with PEG alone, did not elevate their [Ca2+]i as was characteristic of the hepatocytes from the nonseptic rats. The treatment of septic rats with SOD-PEG was effective in restoring Ca2+ influx, cellular exchangeable Ca2+, [Ca2+]i, and the [Ca2+]i response to vasopressin to levels found in the control and sterile groups. These findings support the concept that the generation of the superoxide free radical leads to Ca2+i-related derangements and related cell/organ dysfunction in sepsis.