Nitrate increases in skeletal muscle peak power do not involve changes in sarcomeric protein phosphorylation and require whole‐body physiological pathways

Abstract

Acute dietary nitrate supplementation in humans (within 2 hours) increases limb muscle peak power. In old mice, chronic (14 days) dietary nitrate supplementation increases diaphragm peak power. However, mechanisms of dietary nitrate effects on contractile mechanics are not fully understood. It is unclear whether nitrate ions directly or products downstream of the nitrate‐nitrite‐nitric oxide (NO) reductive pathway are responsible for changes in muscle contractile function. Increases in power likely involve post‐translational modification of myofibrillar proteins – phosphorylation being an established effect of NO signaling. We determined the phosphorylation status of myofibrillar proteins from diaphragms of 24 month old mice supplemented with nitrate (n = 8) or control (n = 6) and found no difference for myosin regulatory light chain, myosin binding protein c, tropomyosin, desmin or troponin I. Regulatory light chain phosphorylation signal normalized to total protein was 1.696 ± 0.139 and 1.699 ± 0.105 for control and nitrate‐supplemented animals, respectively. To examine a direct effect of nitrate on muscle cells, we exposed isolated diaphragm bundles from young mice in vitro to increasing concentrations of NaNO3. In vitro NaNO3 (15 min) had no effect on diaphragm peak power or isometric force (P > 0.05). Specifically, power (% control) was −1.06 ± 0.20 (0.5 mM), −1.73 ± 0.79 (1 mM), −2.64 ± 2.14 (2 mM), and −2.40 ± 2.40 (4 mM). Overall, our study shows that the increase in diaphragm power of aged mice elicited by chronic dietary nitrate supplementation does not involve changes in phosphorylation of key sarcomeric proteins that regulate contractile function. Moreover, our data from in vitro experiments suggest no direct effect of nitrate ions on mammalian skeletal muscle contractile function. Instead, dietary nitrate effects on muscle function appear to require whole‐body physiological mechanisms and actions of molecules downstream of nitrate.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.