1. From the Department of Anatomy and Cell Biology (M.C.Z., E.L., R.V.S., R.L.D.), Free Radical and Radiation Biology Program, Department of Radiation Oncology (M.C.Z., R.L.D.), and The Cardiovascular Center (R.V.S., R.L.D.), The University of Iowa, Roy J. and Lucille A. Carver College of Medicine, Iowa City.