1. School of Biomedical Sciences, Nottingham University Medical School, Queens Medical Centre, Nottingham NG7 2UH, U.K.
2. Division of Diabetes, Department of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, U.S.A.
3. FRAME Alternatives Laboratory, Nottingham University Medical School, Queens Medical Centre, Nottingham NG7 2UH, U.K.