Biochemical and Morphometric Properties of Mitochondrial Populations in Human Muscle Fibres

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Abstract
Two mitochrondrial 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 enzymatic digestion and further mechanical disintegration, recovery 18-21%. The subsarcolemmal mitochondria were morphologically defined as those located within 2 .mu.m from the sarcolemma membrane and the intermyofibrillar mitochrondria as those located in the rest of the fiber. 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 mitochrondrial volume density 2- to 3-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. Both subpopulations of muscle mitochrondria are able to adapt quantitatively and/or qualitatively. 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 mitochrondria.