Nitrite lowers the oxygen cost of ATP supply in skeletal muscle cells by stimulating the rate of glycolytic ATP synthesis

Dietary nitrate lowers the oxygen cost of human exercise. This effect has been suggested to result from stimulation of coupling efficiency of skeletal muscle oxidative phosphorylation by reduced nitrate derivatives. In this paper, we report the acute effects of sodium nitrite on the bioenergetic behaviour of L6 myocytes. At odds with improved efficiency of mitochondrial ATP synthesis, extracellular flux analysis reveals that a [1/2]-hour exposure to NaNO2 (0.1 - 5 {micro}M) significantly decreases mitochondrial coupling efficiency in static myoblasts and tends to lower it in spontaneously contracting myotubes. Unexpectedly, NaNO2 stimulates the rate of glycolytic ATP production in both myoblasts and myotubes. Increased ATP supply through glycolysis does not emerge at the expense of oxidative phosphorylation, which means that NaNO2 acutely increases the rate of overall myocellular ATP synthesis, highly significantly so in myoblasts and tending towards significance in contractile myotubes. Notably, NaNO2 exposure shifts myocytes to a more glycolytic phenotype. Mitochondrial oxygen consumption does not decrease after NaNO2 exposure, and non-mitochondrial respiration tends to drop. When total ATP synthesis rates are normalised to total cellular oxygen consumption rates, it thus transpires that NaNO2 lowers the oxygen cost of ATP supply in L6 myocytes.