Abstract
823 We previously demonstrated a fourfold variation in the slope of the δGATP:QO2 relationship in isolated, mixed skeletal muscle mitochondria across a physiological range of pyruvate concentrations. The purpose of this study was to quantitatively evaluate the role of pyruvate availability on the δGATP:QO2 relationship in mitochondria isolated from skeletal muscle homogeneous (98%) in Type I fibers. Mitochondria were isolated from rabbit soleus and incubated in KCl-based media at 37°C. Various energy states were fixed by manipulating added phosphocreatine/creatine ratios in the presence of 5 mM ATP, 10 mM Pi, and 25U creatine kinase while QO2 was assessed polarographically. Malate (1.0 mM) was added and pyruvate was titrated in to yield 10 uM to 100 uM concentrations. Across all pyruvate concentrations, there was a strong, linear relationship between δGATP and QO2. In contrast to our results in mixed skeletal muscle, the slope of this relationship was only 2.6-fold greater at 100 uM pyruvate (.1101) relative to 10 uM pyruvate (.0425). These results confirm that, for a given QO2, a decrease in pyruvate concentration is associated with a fall in energy state (δGATP). In addition, the results suggest that, at a given QO2, a decrease in pyruvate concentration is associated with a relatively smaller decline in energy state (δGATP) in Type I mitochondria.
Published Version
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