H-1 and P-31 magnetization transfer studies of hindleg muscle in wild-typeand creatine kinase-deficient mice

The authors addressed the hypothesis that interactions with creatine kinase (CK) play a role in the off-resonance magnetization transfer (MT) effect o f creatine in skeletal muscle. Toward that aim,H-1 MT studies were done on hindleg muscle in wild-type mice and in transgenic mice, lacking cytoplasmi c CK and/or mitochondrial CK. The H-1 MT effect was essentially identical i n wild-type muscle and the two single CK knock-out muscles, while moderatel y decreased in tissue lacking both CK isoforms. P-31-NMR showed no off-reso nance P-31 MT effect in skeletal muscle for PCr in any of the mice, while t he enzymatic CK reaction flux was circa 0.2-0.3 sec(-1) in the wild-type mu scle and in muscle deficient in mitochondrial CK. The CK enzyme flux was ne gligible in the other two CK knock-outs, These data suggest that CK plays a minor role in the H-1 MT effect of creatine. Irrespective of the underlyin g mechanism the creatine MT phenomenon probably has no significant conseque nces for the thermodynamic availability of total creatine to the CK reactio n. Magn Reson Med 43:657-664, 2000. (C) 2000 Wiley-Liss, Inc.