1. Departments of Physiology (C.X.D., W.Z., C.S., K.J.R., P.L.B.), University of Toronto, Toronto, Ontario M5S 1A8 Canada
2. Department of Paediatric Laboratory Medicine (C.A.), Physiology and Experimental Medicine, Toronto M5G 1X8, Canada
3. Centre National de la Recherche Scientifique (S.R.), Institut Curie, Paris, 75248 France
4. Inserm (M.H.), Hôpital St-Antoine, Paris, 75005 France
5. Departments of Pediatrics (T.G.), University of Toronto, Toronto, Ontario M5S 1A8 Canada
6. Research Institute (T.G.), The Hospital for Sick Children, Toronto M5G 1X8, Canada
7. Departments of Medicine (P.L.B.), University of Toronto, Toronto, Ontario M5S 1A8 Canada