TRANSMURAL SATURATION-TRANSFER ANALYSIS OF THE CREATINE-KINASE SYSTEMIN THE MAMMALIAN HEART

P-31 NMR spatial localization and saturation transfer techniques were combined to enable the transmural measurement of the forward creatine kinase (CK) rate (ATP:creatine N-phosphotransferase, EC 2.7.3.2.) in t he in vivo canine myocardium. Five epicardial towards endocardial regi ons of the left ventricle (LV) were simultaneously examined using spat ially localized voxels. Although intraleft ventricular CP/ATP ratios w ere constant, the pseudo first order rate constant (k') and the forwar d creatine kinase rate (R(f)) displayed a 61% variation across the LV wall. Because CK levels and calculated [ADP], [CP] and pH are transmur ally invariant in the normal left ventricle, the observed changes in t he R(f) could not be explained by changes in the absolute levels of th ese substrates and of creatine kinase. In addition, because myocardial oxygen consumption rates are known to be higher in the endocardium, t hese results imply that forward creatine kinase rates are not directly related to oxidative phosphorylation rates.