1. Departments of Anatomy and
2. Department of Physiology and Biophysics and Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4790;
3. Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520; and
4. Molecular Medicine and Renal Units, Beth Israel Deaconess Medical Center and Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02215