Refaat E. Gabr1, AbdelMonem M. El-Sharkawy1, Michael Schr2, Robert G. Weiss1,3, Paul A. Bottomley1
1Division of MR Research, Johns Hopkins University, Baltimore, MD, United States; 2Philips Healthcare, Cleveland, OH, United States; 3Division of Cardiology, Johns Hopkins University, Baltimore, MD, United States
Phosphocreatine (PCr) is central to muscle energetics where it putatively serves as a temporal-spatial buffer, transferring high-energy phosphate between the mitochondria and myofibrils by means of diffusion in the cytosol. We report the first measurements of PCr diffusion (DPCr) in human calf muscle using localized 31P MRS as a function of diffusion time and orientation in eight healthy subjects. We find a DPCr of 0.3-0.8x10-3 mm2/s that is both anisotropic and shows evidence of restricted diffusion. Nevertheless, diffusion appears sufficiently fast to traverse the expected distances between mitochondria and myofibrils within the half-life of PCr in the creatine kinase reaction.