Fiber-type differences in muscle mitochondrial profiles

Abstract

Although striated muscles differ in mitochondrial content, the extent of fiber-type specific mitochondrial specializations is not well known. To address this issue, we compared mitochondrial structural and functional properties in red muscle (RM), white muscle (WM), and cardiac muscle of rainbow trout. Overall preservation of the basic relationships between oxidative phosphorylation complexes among fiber types was confirmed by kinetic analyses, immunoblotting of native holoproteins, and spectroscopic measurements of cytochrome content. Fiber-type differences in mitochondrial properties were apparent when parameters were expressed per milligram mitochondrial protein. However, the differences diminished when expressed relative to cytochrome oxidase (COX), possibly a more meaningful denominator than mitochondrial protein. Expressed relative to COX, there were no differences in oxidative phosphorylation enzyme activities, pyruvate-based respiratory rates, H2O2 production, or state 4 proton leak respiration. These data suggest most mitochondrial qualitative properties are conserved across fiber types. However, there remained modest differences ( approximately 50%) in stoichiometries of selected enzymes of the Krebs cycle, beta-oxidation, and antioxidant enzymes. There were clear differences in membrane fluidity (RM > cardiac, WM) and proton conductance (H+/min/mV/U COX: WM > RM > cardiac). The pronounced differences in mitochondrial content between fiber types could be attributed to a combination of differences in myonuclear domain and modest effects on the expression of nuclear- and mitochondrially encoded respiratory genes. Collectively, these studies suggest constitutive pathways that transcend fiber types are primarily responsible for determining most quantitative and qualitative properties of mitochondria.

Rapid mitochondrial adjustments in response to short-term hypoxia and re-oxygenation in the Pacific oysterCrassostrea gigas

“…The concentrations of cytochromes a, b, c 1 and c from the electron transport chain were quantified by difference spectra according to Leary et al (Leary et al, 2003). Six hundred micrograms of mitochondrial proteins (40μl of mitochondrial suspension) were diluted in 960μl of phosphate buffer (NaH 2 PO 4 and Na 2 HPO 4 50mmoll −1 pH7.8 at 25°C) without Triton-X.…”

Regulation of Carnitine Palmitoyltransferase (CPT) I during Fasting in Rainbow Trout (Oncorhynchus mykiss) Promotes Increased Mitochondrial Fatty Acid Oxidation

“…Fatty acid oxidation was assayed using a modified protocol for human skeletal muscle (Bezaire et al 2006) and respiration buffer for fish (Leary et al 2003). Palmitate oxidation was determined at room temperature by measuring trapped 14 C from labeled CO 2 production after a 30-min incubation of viable mitochondria in a sealed system.…”

Characterization of Mitochondrial Content and Respiratory Capacities of Broiler Chicken Skeletal Muscles with Different Muscle Fiber Compositions

“…Mitochondria are centers of aerobic metabolism that generate the bulk of ATP needed to maintain cellular functions based on a highly organized catabolic system consisting of the tricarboxylic acid (TCA) cycle, fatty acid import by the carnitine palmitoyltransferase (CPT) system, and downstream β-oxidation and electron-transferring pathways. Several recent studies have shown that depending on the respiratory capacity of the muscle, specific mitochondrial phenotypes exist in metabolically different muscle fibers in several vertebrates, such as pigs, rats, and rainbow trout (Glancy and Balaban, 2011;Leary et al, 2003;Picard et al, 2012;Ponsot et al, 2005).…”