31P NMR studies of creatine kinase flux in M-creatine kinase-deficient mouse heart.

Hearts of wild-type and cytosolic muscle creatine kinase (M-CK)-knockout mice were perfused with Krebs-Henseleit buffer containing 10 mM glucose and 5 mM pyruvate and studied during pacing at 400 and 600 beats/min and during K+ arrest. Phosphocreatine (PCr) and ATP concentrations in M-CK-deficient hearts were not significantly different from those in wild-type hearts. With the use of31P NMR saturation transfer, the flux mediated predominantly by mitochondrial creatine kinase (Mi-CK) was clearly detected in M-CK-deficient hearts. Mi-CK flux was 4.8 ± 0.6 and 4.5 ± 0.6 mM/s during pacing at 400 and 600 beats/min, respectively, and was 3.5 ± 0.4 mM/s during cardiac arrest. In control hearts total CK flux was 7.8 ± 1.1 and 6.6 ± 1.3 mM/s during pacing at 400 and 600 beats/min, respectively, and decreased to 3.8 ± 0.5 mM/s during arrest. It is suggested that the relative contribution of Mi-CK to the total NMR-measured CK flux in the wild-type heart is higher than that of the homodimeric M-CK isoform (MM-CK).