Biochemical and Morphometric Properties of Mitochondrial Populations in Human Muscle Fibres

Abstract

Two mitochondrial subpopulations were evaluated with biochemical and morphological techniques in human gastrocnemius muscle of 10 patients with peripheral arterial insufficiency and 12 control individuals. The subsarcolemmal mitochondria were released by gentle homogenization, with a recovery of 32-37%, and the intermyofibrillar by enzymic digestion and further mechanical disintegration, recovery 18-21%. The subsarcolemmal mitochondria were morphologically defined as those located within 2 micron from the sarcolemma membrane and the intermyofibrillar mitochondria as those located in the rest of the fibre. In the controls the intermyofibrillar mitochondria had a lower respiratory ratio than the subsarcolemmal, owing to a higher state II respiration. The subsarcolemmal space, which contained 25% of the mitochondria, had a mitochondrial volume density two- to three-fold that of the intermyofibrillar space in the controls. The patients, who had a 48-64% higher oxidative enzyme capacity in their muscle tissue, had higher respiratory rate and respiratory control index with similar ADP/O ratio in the subsarcolemmal fraction in comparison with the controls. The citrate synthase activity was higher in both mitochondrial fractions of the patients. The volume densities of mitochondria, total as well as for both subpopulations, were also higher in the patients, which was further reflected in higher yields of mitochondrial protein. The results demonstrate that both subpopulations of muscle mitochondria are able to adapt quantitatively and/or qualitatively. Furthermore, they show that the increased oxidative enzyme capacity of the patients is associated with an increased quantity of both mitochondrial populations and a qualitative improvement of the respiratory activity of the subsarcolemmal mitochondria.

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

“…As noted by Dr Green, some studies using mitochondria from patients with PAD have shown normal function, 37,68 but others have shown abnormalities in oxidative function. 27 All of these studies must be interpreted cautiously.…”

“…26,48 Yet, maximal mitochondrial respiration and activities of respiratory chain enzymes are normal in PAD 3,37,68 ; whereas they can be less than 20À30% of control values in mitochondrial myopathies. 67,74 The affirmative argument rests partly on differences in enzyme ratios (e.g.…”

“…NADH dehydrogenase=citrate synthase) between PAD and controls. While altered enzyme ratios might be indicative of cellular stress, interpretation of their functional significance is very difficult given that the absolute activities of these enzymes are normal 3,68 and that the enzyme ratios did not correlate significantly with peak VO 2 . 26 In mitochondrial myopathies, peak VO 2 is similar to that seen in PAD (i.e.…”

“…When mitochondria were isolated from the gastrocnemius medialis muscle of the most ischemic limb in claudicants, the maximum rates of pyruvate oxidation and the P:O ratio were normal. 68 More recently, we performed a similar procedure in claudicants and observed that the rates of mitochondrial ATP synthesis in the presence of pyruvate, an esterified fatty acid or both were also normal. 37 These data show that the consumption of O 2 , synthesis of ATP and the P:O ratio in mitochondria isolated from the calf muscle of claudicants are normal.…”

Capillary ultrastructure and mitochondrial volume density in skeletal muscle in relation to reduced exercise capacity of patients with intermittent claudication

“…Pericapillary basement membrane thickening (7,8,24) and alterations of the volume density (V v ) of mitochondria (V v mito ) (1,15) are examples of ultrastructural changes in skeletal muscle in patients with CLI, the late, most severe stages of PAD. However, skeletal muscle samples from CLI patients are heterogeneous and contain large deposits of fat and connective tissue, and there is a higher proportion of degenerated fibers compared with that observed in patients with IC (11), which limits their potential to be used in quantitative investigations.…”