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

Abstract

<jats:p>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 cultured rat (L6) myocytes. At odds with improved efficiency of mitochondrial ATP synthesis, extracellular flux analysis reveals that a ½-hour exposure to NaNO<jats:sub>2</jats:sub> (0.1–5 μM) does not affect mitochondrial coupling efficiency in static myoblasts or in spontaneously contracting myotubes. Unexpectedly, NaNO<jats:sub>2</jats:sub> 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 NaNO<jats:sub>2</jats:sub> acutely increases the rate of overall myocellular ATP synthesis, significantly so in myoblasts and tending towards significance in contractile myotubes. Notably, NaNO<jats:sub>2</jats:sub> exposure shifts myocytes to a more glycolytic bioenergetic phenotype. Mitochondrial oxygen consumption does not decrease after NaNO<jats:sub>2</jats:sub> exposure, and non-mitochondrial respiration tends to drop. When total ATP synthesis rates are expressed in relation to total <jats:italic>cellular</jats:italic> oxygen consumption rates, it thus transpires that NaNO<jats:sub>2</jats:sub> lowers the oxygen cost of ATP supply in cultured L6 myocytes.</jats:p>