Isoforms of creatine kinase: MM in the study of skeletal muscle damage.

Isoforms of creatine kinase (CK) MM have been analysed in plasma from normal subjects and patients with muscular dystrophy using isoelectric focusing techniques. Most plasma samples analysed contained three isoforms of CK-MM of isoelectric points 7.26 (MMI), 6.85 (MMII) and 6.45 (MMIII) although in some plasma samples two additional isoforms of isoelectric points 7.12 and 6.65 were seen. Patients with muscular dystrophy were found to have a generally higher proportion of CK-MMI in their plasma than normal subjects and this was relatively unaffected by large variations in the total creatine kinase activity. By comparison eccentric exercise in normal subjects was found to result in a large increase in total plasma CK activity which then declined to normal over a period of approximately 6 days. CK-MMI was found to increase initially followed by CK-MMII and CK-MMIII. Analysis of the isoforms in biopsy samples of human muscle revealed the presence of two of the bands found in plasma (CK-MMI and MMII) and a third muscle specific isoform, while incubation of muscle homogenates in plasma induced the formation of CK-MMIII and the two isoforms of pI 7.12 and 6.65. It is concluded that analyses of CK-MM isoforms in human plasma can provide useful information on the extent and relative time course following an episode of muscle damage but that in patients with muscular dystrophy the large variations in plasma CK activity are not reflected in the proportion of CK found in each isoform.(ABSTRACT TRUNCATED AT 250 WORDS)