Incubation with sodium nitrite attenuates fatigue development in intact single mouse fibres at physiological PO2

Abstract

Dietary nitrate (NO3−) supplementation, which increases plasma nitrite (NO2−) concentration, has been reported to attenuate skeletal muscle fatigue development. Sarcoplasmic reticulum (SR) calcium (Ca2+) release is enhanced in isolated single skeletal muscle fibres following NO3− supplementation or NO2− incubation at a supra‐physiological PO2 but it is unclear whether NO2− incubation can alter Ca2+ handling and fatigue development at a near‐physiological PO2. We hypothesised that NO2− treatment would improve Ca2+ handling and delay fatigue at a physiological PO2 in intact single mouse skeletal muscle fibres. Each muscle fibre was perfused with Tyrode's solution pre‐equilibrated with either 20% (PO2∼150 Torr) or 2% O2 (PO2 = 15.6 Torr) in the absence and presence of 100 µM NaNO2. At supra‐physiological PO2 (i.e. 20% O2), time to fatigue was lowered by 34% with NaNO2 (control: 257 ± 94 vs. NaNO2: 159 ± 46 s, d = 1.63, P<0.05), but extended by 21% with NaNO2 at 2% O2 (control: 308 ± 217 vs. NaNO2: 368 ± 242 s, d = 1.14, P<0.01). During the fatiguing contraction protocol completed with NaNO2 at 2% O2, peak cytosolic Ca2+ concentration ([Ca2+]c) was not different (P>0.05) but [Ca2+]c accumulation between contractions was lower, concomitant with a greater SR Ca2+ pumping rate (P<0.05) compared to the control condition. These results demonstrate that increased exposure to NO2− blunts fatigue development at near‐physiological, but not at supra‐physiological, PO2 through enhancing SR Ca2+ pumping rate in single skeletal muscle fibres. These findings extend our understanding of the mechanisms by which increased NO2− exposure can mitigate skeletal muscle fatigue development.