Aims: 

This study addresses the importance of strict structural organization of the slow-twitch muscle's cell in determining the type of control over mitochondrial oxidative phosphorylation and the nature of intracellular energy transfer between mitochondria and ATPases.

Methods: 

The function of mitochondria and their interaction with ATPases was compared between the adult rat cardiomyocytes and m. soleus cells (RMC), both expressing regular and stable mitochondrial arrangement and cultured cardiac HL-1 cells with irregular and dynamic mitochondrial network, after permeabilisation of the cells with saponin. The mitochondrial function was assessed by respirometry and the expression of adenylate kinase (AK) and creatine kinase (CK) was assessed by RT-PCR, western blotting and native electrophoresis.

Results: 

Respirometry revealed a 20-30 times lower apparent Km for exogenous ADP in stimulating respiration in the HL-1 cells than in RMC that suggests less restricted ADP diffusion in HL-1 cells. While in RMC the endogenous ADP flux from ATPases was reduced after activation of oxidative phosphorylation (OxPhos) due to direct ADP channelling (DAC) to mitochondria, the DAC was absent in HL-1 cells. The expression of mitochondrial (mit) and cytosolic (cyt) isoforms of CK and AK was revealed in both types of cells, but with much lower mit-CK protein and activity in HL-1 cells than in RMC. The mit-CK and mit-AK was found to be coupled to OxPhos in RMC, whereas in HL-1 cells mit-AK exclusively was coupled to OxPhos.

Conclusion: 

High level of structural organization of RMC gives rise to formation of complexes of ATPases and mitochondria, with CK- and AK-networks and DAC ensuring energy transfer and metabolic feedback within the complexes. In contrast, the HL-1 cells having less organized structure rely upon a simple diffusion of adenine nucleotides facilitated by AK-network for energy transfer.