[Show abstract][Hide abstract] ABSTRACT: In this review we summarize the main structural and functional data on the role of thephosphocreatine (PCr) – creatine kinase (CK) pathway in the compartmentalized energy-transfer in cardiac cells. Mitochondrial creatine kinase, MtCK, fixed by cardiolipin molecules
in the vicinity of the adenine nucleotide translocator is a key enzyme in this pathway. Direct
transfer of ATP and ADP between these proteins has been revealed both in experimental
studies on the kinetics of the regulation of mitochondrial respiration and by mathematical
modelling as a main mechanism of functional coupling of PCr production to oxidative
phosphorylation. In the cells in vivo or in the permeabilized cells in situ, this coupling is
reinforced by limited permeability of the outer membrane of the mitochondria for adenine
nucleotides due to the contacts with cytoskeletal proteins. Due to these mechanisms, at least
80 % of total energy is exported from mitochondria by PCr molecules. Mathematical
modelling of the intracellular diffusion and energy transfer shows that the main function of
the PCr – CK pathway is to connect different pools (compartments) of ATP and in this way to
overcome the local restrictions of the diffusion of adenine nucleotides due to high degree of
structural organization of cardiac cells.
[Show abstract][Hide abstract] ABSTRACT: The control of mitochondrial function is a cardinal issue in the field of cardiac bioenergetics, and the analysis of mitochondrial regulations is central to basic research and in the diagnosis of many diseases. Interaction between cytoskeletal proteins and mitochondria can actively participate in mitochondrial regulation. Potential candidates for the key roles in this regulation are the cytoskeletal proteins plectin and tubulin. Analysis of cardiac cells has revealed regular arrangement of β-tubulin II, fully co-localized with mitochondria. β-Tubulin IV demonstrated a characteristic staining of branched network, β-tubulin III was matched with Z-lines, and β-tubulin I was diffusely spotted and fragmentary polymerized. In contrast, HL-1 cells were characterized by the complete absence of β-tubulin II. Comparative analysis of cardiomyocytes and HL-1 cells revealed a dramatic difference in the mechanisms of mitochondrial regulation. In the heart, colocalization of β-tubulin isotype II with mitochondria suggests that it can participate in the coupling of ATP-ADP translocase (ANT), mitochondrial creatine kinase (MtCK), and VDAC (ANT-MtCK-VDAC). This mitochondrial supercomplex is responsible for the efficient intracellular energy transfer via the phosphocreatine pathway. Existing data suggest that cytoskeletal proteins may control the VDAC, contributing to maintenance of mitochondrial and cellular physiology.
Preview · Article · Apr 2013 · Frontiers in Physiology
[Show abstract][Hide abstract] ABSTRACT: Mitochondria are dynamic structures for which fusion and fission are well characterized for rapidly dividing cells in culture. Based on these data, it has recently been proposed that high respiratory activity is the result of fusion and formation of mitochondrial reticulum, while fission results in fragmented mitochondria with low respiratory activity. In this work we test the validity of this new hypothesis by analyzing our own experimental data obtained in studies of isolated heart mitochondria, permeabilized cells of cardiac phenotype with different mitochondrial arrangement and dynamics. Additionally, we reviewed published data including electron tomographic investigation of mitochondrial membrane-associated structures in heart cells. Oxygraphic studies show that maximal ADP-dependent respiration rates are equally high both in isolated heart mitochondria and in permeabilized cardiomyocytes. On the contrary, these rates are three times lower in NB HL-1 cells with fused mitochondrial reticulum. Confocal and electron tomographic studies show that there is no mitochondrial reticulum in cardiac cells, known to contain 5,000-10,000 individual, single mitochondria, which are regularly arranged at the level of sarcomeres and are at Z-lines separated from each other by membrane structures, including the T-tubular system in close connection to the sarcoplasmic reticulum. The new structural data in the literature show a principal role for the elaborated T-tubular system in organization of cell metabolism by supplying calcium, oxygen and substrates from the extracellular medium into local domains of the cardiac cells for calcium cycling within Calcium Release Units, associated with respiration and its regulation in Intracellular Energetic Units.
Full-text · Article · Dec 2012 · Journal of Bioenergetics
[Show abstract][Hide abstract] ABSTRACT: A broad spectrum of beneficial effects has been ascribed to creatine (Cr), phosphocreatine (PCr) and their cyclic analogues cyclo-(cCr) and phospho-cyclocreatine (PcCr). Cr is widely used as nutritional supplement in sports and increasingly also as adjuvant treatment for pathologies such as myopathies and a plethora of neurodegenerative diseases. Additionally, Cr and its cyclic analogues have been proposed for anti-cancer treatment. The mechanisms involved in these pleiotropic effects are still controversial and far from being understood. The reversible conversion of Cr and ATP into PCr and ADP by creatine kinase, generating highly diffusible PCr energy reserves, is certainly an important element. However, some protective effects of Cr and analogues cannot be satisfactorily explained solely by effects on the cellular energy state. Here we used mainly liposome model systems to provide evidence for interaction of PCr and PcCr with different zwitterionic phospholipids by applying four independent, complementary biochemical and biophysical assays: (i) chemical binding assay, (ii) surface plasmon resonance spectroscopy (SPR), (iii) solid-state (31)P-NMR, and (iv) differential scanning calorimetry (DSC). SPR revealed low affinity PCr/phospholipid interaction that additionally induced changes in liposome shape as indicated by NMR and SPR. Additionally, DSC revealed evidence for membrane packing effects by PCr, as seen by altered lipid phase transition. Finally, PCr efficiently protected against membrane permeabilization in two different model systems: liposome-permeabilization by the membrane-active peptide melittin, and erythrocyte hemolysis by the oxidative drug doxorubicin, hypoosmotic stress or the mild detergent saponin. These findings suggest a new molecular basis for non-energy related functions of PCr and its cyclic analogue. PCr/phospholipid interaction and alteration of membrane structure may not only protect cellular membranes against various insults, but could have more general implications for many physiological membrane-related functions that are relevant for health and disease.
[Show abstract][Hide abstract] ABSTRACT: This review describes the recent experimental data on the importance of the VDAC-cytoskeleton interactions in determining the mechanisms of energy and metabolite transfer between mitochondria and cytoplasm in cardiac cells. In the intermembrane space mitochondrial creatine kinase connects VDAC with adenine nucleotide translocase and ATP synthase complex, on the cytoplasmic side VDAC is linked to cytoskeletal proteins. Applying immunofluorescent imaging and Western blot analysis we have shown that β2-tubulin coexpressed with mitochondria is highly important for cardiac muscle cells mitochondrial metabolism. Since it has been shown by Rostovtseva et al. that αβ-heterodimer of tubulin binds to VDAC and decreases its permeability, we suppose that the β-tubulin subunit is bound on the cytoplasmic side and α-tubulin C-terminal tail is inserted into VDAC. Other cytoskeletal proteins, such as plectin and desmin may be involved in this process. The result of VDAC-cytoskeletal interactions is selective restriction of the channel permeability for adenine nucleotides but not for creatine or phosphocreatine that favors energy transfer via the phosphocreatine pathway. In some types of cancer cells these interactions are altered favoring the hexokinase binding and thus explaining the Warburg effect of increased glycolytic lactate production in these cells. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism.
Full-text · Article · Jan 2012 · Biochimica et Biophysica Acta
[Show abstract][Hide abstract] ABSTRACT: In this review we analyze the recent important and remarkable advancements in studies of compartmentation of adenine nucleotides in muscle cells due to their binding to macromolecular complexes and cellular structures, which results in non-equilibrium steady state of the creatine kinase reaction. We discuss the problems of measuring the energy fluxes between different cellular compartments and their simulation by using different computer models. Energy flux determinations by (18)O transfer method have shown that in heart about 80% of energy is carried out of mitochondrial intermembrane space into cytoplasm by phosphocreatine fluxes generated by mitochondrial creatine kinase from adenosine triphosphate (ATP), produced by ATP Synthasome. We have applied the mathematical model of compartmentalized energy transfer for analysis of experimental data on the dependence of oxygen consumption rate on heart workload in isolated working heart reported by Williamson et al. The analysis of these data show that even at the maximal workloads and respiration rates, equal to 174 μmol O(2) per min per g dry weight, phosphocreatine flux, and not ATP, carries about 80-85% percent of energy needed out of mitochondria into the cytosol. We analyze also the reasons of failures of several computer models published in the literature to correctly describe the experimental data.
Full-text · Article · Dec 2011 · International Journal of Molecular Sciences
[Show abstract][Hide abstract] ABSTRACT: To study the effects of physical training at mild intensities on skeletal muscle energy metabolism in eight patients with chronic obstructive pulmonary disease (COPD) and eight paired healthy sedentary subjects.
Energy metabolism of patients and controls vastus lateralis muscle was studied before and after 3 months of cycling training at mild exercises intensities.
The total amount of work accomplished was about 4059 ± 336 kJ in patients with COPD and 7531 ± 1693 kJ in control subjects. This work corresponds to a mechanical power set at 65.2 ± 7.5% of the maximum power for patients with COPD and 52 ± 3.3% of the maximum power in control group. Despite this low level of exercise intensities, we observed an improvement in mitochondrial oxidative phosphorylation through the creatine kinase system revealed by the increased apparent K(m) for ADP (from 105.5 ± 16.1 to 176.9 ± 26.5 μm, P < 0.05 in the COPD group and from 126.9 ± 16.8 to 177.7 ± 17.0, P > 0.05 in the control group). Meanwhile, maximal mechanical and metabolic power increased significantly from 83.1 ± 7.1 to 91.3 ± 7.4 Watts (P < 0.05) and from 16 ± 0.8 to 18.7 ± 0.98 mL O(2) kg(-1) min(-1) (P < 0.05) only in the COPD group.
This study shows that physical training at mild intensity is able to induce comparable changes in skeletal muscles oxidative energy metabolism in patients with COPD and sedentary healthy subjects, but different changes of maximal mechanical and metabolic power.
Full-text · Article · Nov 2011 · Acta Physiologica