Cathodally migrating creatine kinase in sera of patients treated with theophylline, and its diagnostic implications.

Sera from 30 patients, selected only on the basis of having serum theophylline concentrations greater than or equal to 18 mg/L, were assayed for total creatine kinase (CK), isoenzyme CK-MB, and cathodally migrating CK (mCK-2). CK-MB was measured by ion-exchange chromatography. mCK-2 was detected by electrophoresis on agarose gel, with fluorometric scanning. The mCK-2 variant was found in 37% of these 30 patients. None of the patients in the mCK-2 group had CK-MB values exceeding the cutoff value associated with myocardial infarction, so extensive cardiac ischemia was considered unlikely. A review of the patients' records supported this conclusion, and no particular association with any specific disease was found among the mCK-2 group. Investigations with use of goat anti-CK-MM and anti-theophylline indicated that neither CK-MM nor theophylline were present in the mCK-2. Results of specific radioimmunoassay for CK-B subunit were negative. The mobility of the mCK-2 peak was unresponsive to 2-mercaptoethanol, suggesting that CK of mitochondrial origin was not present. These results provide insight into the clinical relevance of mCK-2 and some information concerning its composition.