George 2015 BA Thesis
| George M (2015) Assessing mitochondrial lactate oxidation in male rat permeabilized skeletal muscle fibers highlights important experimental considerations. BA Thesis 1-32. |
Abstract: Lactate has been considered a “dead-end” waste product of anaerobic metabolism. However, research continually demonstrates that lactate serves as an important metabolic fuel for many tissues, including skeletal and cardiac muscles, liver and brain. The intracellular lactate shuttle hypothesis posits that lactate generated in the cytosol is oxidized by mitochondrial lactate dehydrogenase (LDH) of the same cell. The details of the shuttle have not been made entirely clear. It has been proposed that such a shuttle operates similarly to the malate-aspartate shuttle; it has also been proposed that the two shuttles are necessarily interconnected in a lactate-malate-aspartate shuttle. We hypothesized that experimental support for robust mitochondrial lactate oxidation requires detailed attention to methodological detail. More specifically, an optimal malate concentration was expected to elicit maximal lactate oxidation in skeletal muscle mitochondria in vitro. To test this hypothesis, rates of mitochondrial respiratory oxygen flux (JO2) were continuously monitored during titration of increasing concentrations of lactate (5-30 mM) atop 5 mM ADP, 1 mM NAD+ and either 0.5 mM or 4 mM malate in saponin-permeabilized red gastrocnemius muscle fibres from Sprague-Dawley (N = 3) and Wistar rats (N = 3). Net lactate-supported JO2 was significantly greater with 0.5 mM malate (two-way ANOVA with repeated measures; main effect for malate concentration, P = .0156). The results of this study suggest that mitochondrial lactate oxidation may indeed depend on multi-dehydrogenase activity outside of the mitochondrial matrix. These results also highlight malate concentration as an important variable to consider when interpreting in vitro phenomena in the context of muscle physiology in vivo. • Keywords: Lactate, Buffer z
• O2k-Network Lab: CA Antigonish Kane DA
Labels: MiParea: Respiration
Organism: Rat
Tissue;cell: Skeletal muscle
Preparation: Permeabilized tissue
Regulation: Substrate Coupling state: OXPHOS Pathway: N HRR: Oxygraph-2k
