1. G. B. Pier, M. Grout, T. S. Zaidi, J. B. Goldberg, Channing Laboratory and Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, 180 Longwood Avenue, Boston, MA 02115-5899, USA.
2. J. C. Olsen, L. G. Johnson, J. R. Yankaskas, Department of Medicine, Division of Pulmonary Diseases, University of North Carolina, Chapel Hill, NC 27599-7020, USA.