1. Departments of Cell Biology and of Physiology and Biophysics and Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama, Birmingham, Alabama 35294-0005;
2. Department of Laboratory Medicine, Cardiovascular Research Institute, University of California, San Francisco, California 94143-0911; and
3. Departments of Physiology and Pediatrics and Cystic Fibrosis Research Center, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205