Disruption of the creatine kinase (CK) system in hearts of CK-deficient mice leads to changes in ultrastructure and regulation of mitochondrial respiration. We expected to see similar changes in creatine deficient mice, lacking the enzyme guanidinoacetate methyltransferase (GAMT) to produce creatine. The aim of this study was to characterize the changes in cardiomyocyte mitochondrial organization, regulation of respiration and intracellular compartmentation associated with GAMT-deficiency. Three-dimensional mitochondrial organization was assessed by confocal microscopy. On populations of permeabilized cardiomyocytes, we recorded ADP- and ATP-kinetics of respiration, competition between mitochondria and pyruvate kinase for ADP produced by ATPases, ADP-kinetics of endogenous pyruvate kinase, and ATP-kinetics of ATPases. These data were analyzed by mathematical models to estimate intracellular compartmentation. Quantitative analysis of morphologic and kinetic data, as well as derived model fits show no difference between GAMT-deficient and wildtype mice. We conclude that inactivation of the CK-system by GAMT-deficiency does not alter mitochondrial organization and intracellular compartmentation in relaxed cardiomyocytes. Thus, our results suggest that the healthy heart is able to preserve cardiac function at a basal level in the absence of CK facilitated energy transfer without compromising intracellular organization and regulation of mitochondrial energy homeostasis. This raises questions on the importance of the CK system as a spatial energy buffer in unstressed cardiomyocytes.
- Creatine kinase shuttle
- mitochondrial positioning
- confocal imaging
- intracellular diffusion barriers
- respiration and ATPase kinetics
- Copyright © 2013, American Journal of Physiology - Heart and Circulatory Physiology