The myocardial profile of the cytosolic isozymes of creatine kinase is apparently not related to cyanosis in congenital heart disease

Background: CKMB, the cardiac-specific heterodimer of cytosolic creatine-ki nase (CK), is developmentally and physiologically regulated, tissue hypoxia being a proposed regulator. In patients with cyanotic heart disease the my ocardium:is perfused with partially saturated blood. We questioned whether the myocardium of cyanotic subjects contains higher proportions of CKMB. Materials and Methods: CK activity, the distribution of cytosolic CK isozym es, activity of lactic dehydrogenase (LDH), and tissue protein content were determined in obstructive tissues removed at corrective surgery of patient s with congenital heart defects. Cyanotic (n = 13) and acyanotic (n = 12) s ubjects were compared. Results: In cyanotic and acyanotic patients, CK activity was 8.4 +/- 0.6 an d 7.6 +/- 0.6 IU/mg protein and the proportion of CKMB was 21 +/- 1.4 and 2 2 +/- 2.0% (mean +/- S.E.M), respectively. In the two groups of patients, t he activity related to the B subunit corresponded to the steady-state level of the CKBmRNA. The tissue content of protein and the, activities of CK an d LDH were similar in cyanotic and acyanotic subjects and increased with th e age. Conclusions: The lack of difference in CKMB distribution between the cyanot ic and acyanotic patients may either indicate that hypooxygenation is not a regulator of CK isozyme expression, or may be attributed to the already hi gh proportion of this isozyme in hypertrophied, obstructive tissues. Recrui tment of additional CKMB, in the cyanotic hearts, may thus not be required.