Effects of ischemia on skeletal muscle energy metabolism in mice lacking creatine kinase monitored by in vivo 31P nuclear magnetic resonance spectroscopy

The aim of this study was to provide in vivo experimental evidence for the proposed biological significance of the creatine kinase (CK)/phosphocreatine (PCr) system in the energy metabolism of skeletal muscle. As a test system we compared hindlimb muscle of knockout mice lacking the cytosolic M-type (M-CK-/(-)), the mitochondrial ScMit-type (ScCKmit(-)/(-)), or both creatine kinase isoenzymes (CK-/(-)), and in vivo P-31-NMR was used to monitor metabolic responses during and after an ischemic period. Although single mutants show some subtle specific abnormalities, in general their metabolic responses appear similar to wild type, in contrast to CK-/(-) double mutants. This implies that presence of one CK isoform is both necessary and sufficient for the system to be functional in meeting ischemic stress conditions. The global ATP buffering role of the CK/PCr system became apparent in a 30% decline of ATP in the CK-/(-) mice during ischemia. Both M-CK-/(-) and CK-/(-) showed increased phosphomonoester levels during ischemia, most likely reflecting adaptation to a more efficient utilization of glycogenolysis. While in M-CK-/(-) muscle PCr can still be hydrolyzed to provide P-i for this process, in CK-/(-) muscle only P-i from ATP breakdown is available and P-i levels increase much more slowly. The experiments also revealed that the system plays a role in maintaining pH levels; the CK-/(-) mice showed a faster and more pronounced acidification (pH = 6.6) than muscles of wild type and single knockout mutants (pH = 6.9). Copyright (C) 1999 John Wiley & Sons, Ltd.