Relations between mitochondrial function and contractile types of muscle fibre

Abstract

Skeletal muscle is of major economic importance in meat-producing animals. It is a composite tissue mostly composed of heterogeneous muscle fibres exhibiting various contractile and metabolic properties. The relationships between contractile fibre types and mitochon-drial functioning, a central component of muscular energy metabolism, remain poorly understood. The comprehension of these relations is essential in order to control the impact of the fibre types on the various components of meat quality. A detailed analysis of mitochon-drial functioning, in relation to fibre contractile types, was thus undertaken. The results indicate that, unlike fast IIX and IIB fibres, the regulation of mitochondrial respiration in slow type I fibres and, to a lesser extent, in fast type IIA, is highly specialised with an optimisation of mitochondrial efficiency (coupling between oxidation and phosphorylation, maximal oxidative capacity), a restriction of mitochondrial permeability to ADP and a functional coupling between mitochondrial kinases and ATP production, allowing an efficient energy transfer from mitochondria to myosins. Moreover, the mitochondrial regulation and energy transfers are modulated by a calcium-dependent activation of ATPase activity carried by myosins.