Isozymes of creatine kinase in mammalian cell culures

Abstract

Previous studies on the energy metabolism of rat myocardial cells in culture supported the hypothesis that the creatine-phosphocreatine-creatine kinase system plays an important role in the intracellular transport of energy from the mitochondria to the myofibrils and in the regulation of energy production coupled to energy utilization in this model system. Effective functional compartmentation of ATP could result from the binding of creatine kinase to cellular organelles (e.g., myofibrils and mitochondria) such that high energy charge at the myofibrils is maintained by the reverse creatine kinase reaction, while phosphocreatine is synthesized mainly at the mitochondria in the forward creatine kinase reaction. It was, therefore, essential to demonstrate the presence of mitochondrial creatine kinase in the cultured myocardial cells to support this hypothesis, particularly since the mitochondrial creatine kinase was reportedly absent in fetal hearts. Using electrophoresis on cellulose acetate strips, the mitochondrial creatine kinase isozyme, as well as MM, MB, and BB isozymes, have now been demonstrated in myocardial cultures derived from neonatal rats. The mitochondrial creatine kinase increased with age in culture and with age of animal from which the culture is derived. Furthermore, the addition of creatine to culture media stimulates its synthesis. The mitochondrial creatine kinase isozyme was not detected in nonmuscle cells in culture derived from the neonatal rat hearts, nor in L6 muscle cell line. Phosphocreatine was present in all cells, but the regulation of energy metabolism and energy shuttle by creatine-phosphocreatine-creatine kinase could be operative only in the cells where the mitochondrial creatine kinase is present. This regulatory mechanism provides for an efficient system concomitant with the continuous energy demand of the myocardium; it is not ubiquitous and its development in myocardial cells seems to be triggered postnatally.

Therapeutic Use of Creatine in Brain or Heart Ischemia: Available Data and Future Perspectives

“…The reduction of tension to 25, 50, and 75% of the preanoxic value was delayed compared to controls and PCr provided better protection compared to ATP . In further research, Cr added to the culture medium of cardiac cells was shown to induce an increase in PCr and in mitochondrial CK . Electrophysiological studies revealed that in the main left papillary muscles subjected to a 40 min period of hypoxia PCr pretreatment induced a significant difference of the action potential compared to control animals.…”

“…102 In further research, Cr added to the culture medium of cardiac cells was shown to induce an increase in PCr 103 and in mitochondrial CK. 104 Electrophysiological studies revealed that in the main left papillary muscles subjected to a 40 min period of hypoxia PCr pretreatment induced a THERAPEUTIC USE OF CREATINE IN BRAIN K 9…”

Reduced creatine kinase as a central and peripheral biomarker in Huntington's disease

“…Thus, creatine kinase offsets energy depletion by forming PCr, providing a spatial energy buffer to re-phosphorylate ADP to ATP at cellular sites of energy consumption and, in the reversible reaction, forming PCr and ADP from creatine and ATP at cellular sites of high-energy phosphate production (PCr shuttle hypothesis) [29–32]. As such, CK is critically vital to cellular energy homeostasis and its loss may result in reduced energy stores and subsequent neuronal dysfunction and death in HD.…”