1. S. A. Akhter and W. J. Koch, Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
2. L. M. Luttrell, Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
3. H. A. Rockman, Department of Medicine (Cardiology), University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
4. G. Iaccarino and R. J. Lefkowitz, Howard Hughes Medical Institute, Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.