Magentization transfer study of creatine kinase in myocardium. Potential clinical interest of in vivo enzymology.

Since myocardial contractility relies on the continuous balance of ATP synthesis and ATP degradation, a dynamic estimation of the high energy phosphates (HEP) turnover by magnetization transfer 31P NMR spectroscopy appears to be a more valuable index of heart function than the static evaluation of HEP concentration. The theory of the main magnetization transfer techniques (saturation transfer, inversion transfer) is described as well as a critical evaluation of their application to the determination of creatine kinase (CK) fluxes in myocardium. The determinants of CK flux in vivo is evaluated (total CK activity, isozymic CK expression and concentrations of CK substrates and products). CK flux is shown to vary in relation to contractility during short term stress (hypoxia, ischemia) and in long term adaptation or pathology of the myocardium. The dynamic estimation of energetic flux in vivo is proposed as a non-invasive tool of diagnosis in myocardial pathologies.