Possible Role of Cytoskeleton in Intracellular Arrangement and Regulation of Mitochondria

Abstract

It is a well-known phenomenon that in permeabilized oxidative muscle cells the apparent K m for exogenous ADP in the control of mitochondrial respiration is very high, in the range of 250-350 mM, in contrast with isolated mitochondria in vitro (where the apparent K m for ADP is 15-20 mM: Kummel 1988;Saks et al. 1991Saks et al. , 1993Saks et al. , 1994Saks et al. , 1995Saks et al. , 1998bSaks et al. , 2001Fontaine et al. 1995;Veksler et al. 1995;Kuznetsov et al. 1996; Kay et al. 1997a,b,c;Milner et al. 2000;Anflous et al. 2001;Braun et al. 2001;Seppet et al. 2001;Toleikis et al. 2001;Burelle & Hochachka, 2002;Dos Santos et al. 2002). Simplistic explanation of these differences by the formation of ADP concentration gradients between the medium and the core of the cells can be excluded, since the Brownian movement of ADP in the water solution is much more rapid for a diffusion distance of less than 10 mm than the metabolic turnover of ADP and ATP . A high value of the apparent K m for exogenous ADP is also observed in 'ghost' muscle cells after the extraction of myosin in 800 mM KCl (Kay et al. 1997b). Moreover, we know that the rupture of outer mitochondrial membrane in hyposmotic conditions decreases the value of this parameter (Saks et al. 1993). Thus, in the cells in vivo the low permeability of the outer mitochondrial membrane for ADP and ATP is controlled by some intracellular factors. The decrease of apparent K m for exogenous ADP The origin of significant differences between the apparent affinities of heart mitochondrial respiration for exogenous ADP in isolated mitochondria in vitro and in permeabilized cardiomyocytes or skinned fibres in situ is critically analysed. All experimental data demonstrate the importance of structural factors of intracellular arrangement of mitochondria into functional complexes with myofibrils and sarcoplasmic reticulum in oxidative muscle cells and the control of outer mitochondrial membrane permeability. It has been shown that the high apparent K m for exogenous ADP (250-350 mM) in permeabilized cells and in ghost cells (without myosin) and fibres (diameter 15-20 mm) is independent of intrinsic MgATPase activity. However, the K m may be decreased significantly by a selective proteolytic treatment, which also destroys the regular arrangement of mitochondria between sarcomeres and increases the accessibility of endogenous ADP to the exogenous pyruvate kinase-phosphoenolpyruvate system. The confocal microscopy was used to study the changes in intracellular distribution of mitochondria and localization of cytoskeletal proteins, such as desmin, tubulin and plectin in permeabilized cardiac cells during short proteolytic treatment. The results show the rapid collapse of microtubular and plectin networks but not of desmin localization under these conditions. These results point to the participation of cytoskeletal proteins in the intracellular organization and control of mitochondrial function in the cells in vivo, where mitochondria are incorporated into functional complexes with sa...

Ultrastructural remodeling of fast skeletal muscle fibers induced by invalidation of creatine kinase

“…It has been suggested that the sensitivity of muscle mitochondria to cytosolic ADP depends on the cytoarchitecture and cytoskeleton (1). Because the apparent K m for cytosolic ADP increased in CK Ϫ/Ϫ gastrocnemius muscle in parallel with increased crowding of mitochondria as demonstrated in this study, it is tempting to speculate that high K m for ADP in oxidative muscles is simply a direct consequence of mitochondria being crowded within clusters, leading to decreased access of cytosolic ADP to the mitochondrial surface.…”

VDAC regulation: role of cytosolic proteins and mitochondrial lipids

“…In isolated mitochondria, respiration is characterized by an apparent K m for exogenous ADP that is about 10-fold lower than in permeabilized cells with oxidative metabolism (Appaix et al 2003;Saks et al 1995). In other words, in permeabilized cells with oxidative metabolism ANT is less accessible to cytosolic ADP than in isolated mitochondria.…”

“…In other words, in permeabilized cells with oxidative metabolism ANT is less accessible to cytosolic ADP than in isolated mitochondria. Saks and coauthors (Appaix et al 2003) have found that mild trypsin treatment of permeabilized cardiomyocytes and cardiac fibers resulted in a decrease in apparent K m for ADP, or an increase of MOM permeability up to the level of the high MOM permeability of isolated mitochondria. They also observed that this processes is accompanied by disintegration of the mitochondrial network, which otherwise is very structured in cardiac cells, and by rearrangement of the microtubule network (Appaix et al 2003).…”

“…Saks and coauthors (Appaix et al 2003) have found that mild trypsin treatment of permeabilized cardiomyocytes and cardiac fibers resulted in a decrease in apparent K m for ADP, or an increase of MOM permeability up to the level of the high MOM permeability of isolated mitochondria. They also observed that this processes is accompanied by disintegration of the mitochondrial network, which otherwise is very structured in cardiac cells, and by rearrangement of the microtubule network (Appaix et al 2003). These observations suggested the existence of a protein factor(s) associated with the cytoskeleton, the so called "Factor-X" introduced by Saks and coauthors in mid-1990s, which controls MOM permeability in vivo (Saks et al 1995).…”

Cardiomyopathies Associated with Myofibrillar Myopathies

“…The main effects have been studied on the localization and function of mitochondria. Structural studies of intracellular arrangements of mitochondria into functional complexes with myofibrils and sarcoplasmic reticulum demonstrate their importance in mitochondrial oxydative activity and membrane permeability (Andrienko et al, 2003;Appaix et al, 2003). There are findings with pathological respiratory chain enzyme activities in patients with MFM (Reimann et al, 2003).…”