MiP2005: Session 2

Abstract without presentation                                        Mitochondrial Physiology Network 10.9: 31-32 (2005) - download pdf

 

Effect of muscle mitochondria heterogeneity on O2 transport in muscle fiber at rest and work.

Katherine Lyabakh

Glushkov Institute of Cybernetics, Kiev, Ucraine. - katya@public.icyb.kiev.ua

     Muscle O2 supply is very heterogeneously distributed with high values near capillary and low ones at the lethal corner. Using the ideas concerning O2 supply in some biological objects we tried to examine the possible ways of pO2 equalization in muscle fibers with mitochondrial heterogeneity.

    Contemporary literature is lacking a unified opinion as to physiological role of the two mitochondrial populations - subsarcolemmal (SS) and intermyofibrillar (IMF) - in skeletal and cardiac muscle which differ in their morphological and biochemical properties [1]. The aim of the study is to investigate the impact of heterogeneity of the mitochondria on muscle O2 supply by means of mathematical modeling [2]. We have calculated the рО2 distribution in myocytes under different values of the apparent Michaelis constant for SS and IMF clusters, both varying within the range of 0.5 to 10 mmHg and mitochondria oxygen capacities qO2,ss and qO2,IMF varying within the range of 1 to 30 ml∙min-1∙100 g-1 at rest and work.

    Our investigation at rest revealed that a 2-fold increase in oxygen consumption rate in the SS mitochondria only with unchanged oxygen utilization rate in IMF mitochondria may markedly displace the estimated pO2 histogram to the left. So we suggest that an increased O2 consumption in the SS mitochondrial cluster (for example, by partial uncoupling of respiratory chain in mitochondria of SS cluster) allows to burn ‘extra’ oxygen, converting the energy to heat, which is readily eliminated by capillary blood flow and by heat dissipation from the fiber surface near blood capillaries.

    Investigation at work reveals that one of the approaches for equalizing pO2 distribution and increasing pO2 at the lethal corner is to change the values of qO2,ss and qO2,IMF. According to computations, a significant increase in qO2,ss gives only a slight increase in рО2 at the lethal corner. In this case, a worthy strategy of fight for oxygen might be linked with the hyperplasia of the mitochondria that are located near capillaries and densely packed under the sarcolemma. Another approach is to change the values of Km for O2 in mitochondrial SS and IMF. The calculations have demonstrated that a rise of Кm,SS by 6 to 8 times changes the O2 gradients in the fiber, increases the рО2 value at the lethal corner, reduces the percentage of tissue zones with low values рО2 and shifts the рО2 histogram to the right. Since SS-mitochondria take only small volume of muscle fiber, they can, without noticeable damage to general energy production, increase oxygen flux inside the fiber to IMF mitochondria thereby performing an important function of equalizing the cell рО2.. It contributes to the reduction of oxygen debt production and weakens the local hypoxia in a working skeletal muscle.

1.  Bizeau M, Willis W, Hazel JR (1998) Differential responses to endurance training in subsarcolemmal and intermyofibrillar mitochondria. J. Appl. Physiol. 85: 1279-1284.

2.  Lyabakh KG, Mankovskaya IN (2002) Oxygen transport to skeletal muscle working at VO2max in acute hypoxia: theoretical prediction. Comp. Biochem. Physiol. A. 132: 53-60.


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