Portland State University. Department of Biology
Stanley S. Hillman
Term of Graduation
Date of Publication
Master of Science (M.S.) in Biology
Oxygen in the body, Hydrogen-ion concentration, Mitochondria, Bufo marinus -- Metabolism, Bullfrog -- Metabolism
1 online resource (3, 35 pages)
The concept of maximal oxygen consumption (VO2 max) implies that there is a limit to the amount of oxygen that can be consumed by an organism in a given time. Many attempts have been made to delineate exactly what factor or factors are limiting to VO2 max. Current models focus on the steps over which oxygen must traverse in order to get from the ambient air to the mitochondria. However, no model has addressed the issue of whether or not carbon dioxide flux may impose a limit to VO2 max. Impedance of carbon dioxide flux may have a deleterious effect on intracellular pH, which in turn, may effect mitochondrial oxidative performance.
Experimentally controlled in vitro respiration of isolated skeletal muscle mitochondria can reflect in vivo performance under similar conditions. Skeletal muscle mitochondria were isolated from the "aerobic" toad Bufo marinus and the "anaerobic" frog Rana catesbeiana. Oxidative capacity, or VO2 max, was evaluated for mitochondria subjected to varying physiological pH ranging from 6.1-7.4.
Another aspect of mitochondrial metabolism involves muscle fibre types. In several vertebrates, muscle fibres are specialized for either aerobically or anaerobically driven locomotion, and as a metabolic consequence utilize different sets of substrates. Skeletal muscle mitochondria from B. marinus and R. catesbeiana were allowed to respire in media containing either pyruvate, alpha-ketoglutarate, oxaloacetate, beta-hydroxybutyrate, or octanoyl-carnitine in order to assess whether or not mitochondria from amphibians with different locomotory patterns preferred different substrates.
For both species of amphibian, mitochondrial oxygen consumption was maximal at a pH range of 7.3-7.6 and declined significantly (p<0.05) at all pH<7.3. Respiratory control ratio (RCR) values decreased significantly at all pH<6.9. It therefore appears that mitochondria indeed have a pH optimum (within physiological ranges experienced) and that CO2 flux is a factor that may place limits on VO2 max.
Substrate preference was identical for both species of amphibian corroborating studies which contend both genera of amphibians have mixed skeletal muscle fibre types. Interspecific comparisons revealed that B. marinus had a significantly higher VO2 max in four of the five substrates. This augmented aerobic performance sustains the locomotory metabolic requisites terrestrial excursions demand.
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Duerr, Jeffrey Mark, "An Analysis of the pH Tolerance and Substrate Preference of Isolated Skeletal Muscle Mitochondria from Bufo marinus and Rana catesbeiana" (1991). Dissertations and Theses. Paper 4201.