Sarco/endoplasmic reticulum Ca2+-pump isoform SERCA3a is more resistant to superoxide damage than SERCA2b

Endo/sarcoplasmic reticulum (ER) Ca2+-pumps are important for cell survival and communication but they are inactivated by reactive oxygen species (ROS). We have previously reported that the Ca2+-pump isoform SERCA3a is more resistant than SERCA2b to damage by peroxide. Since peroxide and superoxide differ in their redox potentials, we now report the effects of superoxide on the two Ca2+-pump isoforms. We isolated microsomes from HEK293 cells transiently transfected with SERCA2b or SERCA3a cDNA. We exposed these microsomes to superoxide which was generated using xanthine plus xanthine oxidase and catalase to prevent accumulation of peroxide due to superoxide dismutation. Superoxide damaged the Ca2+- transport activity of both isoforms but SERCA3a was damaged at higher concentrations of superoxide and upon longer periods of exposures than was SERCA2b. Thus the SERCA3a isoform is more resistant than SERCA2b to inactivation by both superoxide and peroxide.