Meeting Abstract
Skeletal muscle fibers tend to grow as large as possible, often to the brink of oxygen diffusion limitation. This appears to be a strategy to minimize the cost of maintaining the membrane potential across the sarcolemma in resting muscle, since large fibers have a lower surface area to volume than small fibers. However, the sarcolemma is but one of many membrane systems in organisms, all of which require energy to maintain transmembrane gradients. We hypothesized that whole animal resting metabolic rate would be positively correlated to membrane lipid content, but unrelated to non-membrane lipid content. We tested this hypothesis in species of tropical freshwater fishes by measuring the oxygen consumption rate at rest using closed-chamber respirometry, and lipid content using thin layer chromatography in the whole animal. The oxygen consumption rate scaled negatively with body mass across all species, as expected. Six classes of lipids were identified: triacylglycerols (TAGs), free fatty acids (FFAs), sterolesters, cholesterol, and two classes of phospholipids. The 3 classes of non-membrane lipids (TAGs, FFAs and sterolesters) were not significantly correlated with oxygen consumption rate. In contrast, the 3 classes of membrane lipids (cholesterol and the two phospholipid classes) were significantly positively correlated with the rate of oxygen consumption. These results indicate that the extent of metabolic compartmentation may be a major contributor to variation in resting metabolic rate.
