Oxygen Exchange Profile in Rat Muscles of Contrasting Fibre Types

Abstract

To determine whether fibre type affects the O2 exchange characteristics of skeletal muscle at the microcirculatory level we tested the hypothesis that, following the onset of contractions, muscle comprising predominately type I fibres (soleus, Sol, 86 % type I) would, based on demonstrated blood flow responses, exhibit a blunted microvascular PO2 (PO2,m, which is determined by the O2 delivery (Q̇O2) to O2 uptake (V̇O2) ratio) profile (assessed via phosphorescence quenching) compared to muscle of primarily type II fibres (peroneal, Per, 84 % type II). PO2,m was measured at rest, and following the rest‐contractions (twitch, 1 Hz, 2–4 V for 120 s) transition in Sol (n= 6) and Per (n= 6) muscles of Sprague‐Dawley rats. Both muscles exhibited a delay followed by a mono‐exponential decrease in PO2,m to the steady state. However, compared with Sol, Per demonstrated (1) a larger change in baseline minus steady state contracting PO2,m (ΔPO2,m) (Per, 13.4 ± 1.7 mmHg; Sol, 8.6 ± 0.9 mmHg, P < 0.05); (2) a faster mean response time (i.e. time delay (TD) plus time constant (τ); Per, 23.8 ± 1.5 s; Sol, 39.6 ± 4.3 s, P < 0.05); and therefore (3) a greater rate of PO2,m decline (ΔPO2,m/τ; Per, 0.92 ± 0.08 mmHg s−1; Sol, 0.42 ± 0.05 mmHg s−1, P < 0.05). These data demonstrate an increased microvascular pressure head of O2 at any given point after the initial time delay for Sol versus Per following the onset of contractions that is probably due to faster Q̇O2 dynamics relative to those of V̇O2.

Inorganic nitrate supplementation improves muscle oxygenation, O2uptake kinetics, and exercise tolerance at high but not low pedal rates

“…Indeed, previous studies have shown that NO 3 Ϫ supplementation can increase muscle blood flow in the running rat (24) and that NO 2 Ϫ infusion can increase blood flow in humans performing forearm exercise (16). The potential for enhanced perfusion with BR is likely to be more pronounced in the microvasculature of fast-twitch muscle, where PO 2 during contractions is lower (8,47), since the reduction of NO 2 Ϫ to NO is augmented as PO 2 declines (14). This might explain why NO 3 Ϫ supplementation has been shown to preferentially distribute blood flow toward (24), and increase microvascular PO 2 within (26), the more fatiguesusceptible fast-twitch muscle fibers in rats and to speed phase II V O 2 kinetics when a greater proportion of fast-twitch muscle fibers are likely to be recruited (12).…”

“…Subjects completed one severe-intensity step test on days 4,5,8, and 9 of each dietary condition (PLA and BR). The same pedal cadence (either 35 or 115 rpm) was applied on days 4 and 5 of the supplementation period with the other cadence applied on days 8 and 9 of the supplementation period.…”

Dietary nitrate supplementation improves sprint and high-intensity intermittent running performance

“…14 Given that the reduction of NO 2 -to NO is potentiated with decreasing O 2 tension van Faassen et al 2009) and that PO 2 is lower in type II compared to type I muscle (Behnke et al 2003;McDonough et al 2005), increasing plasma [NO 2 -] via NO 3 -supplementation may enhance NO 2 --derived NO synthesis and thus performance during exercise at higher intensities. We have previously reported a fall in plasma [NO 2 -] during high-intensity intermittent exercise following NO 3 -supplementation (Wylie et al 2013a;Thompson et al 2015).…”

Linking Pulmonary Oxygen Uptake, Muscle Oxygen Utilization and Cellular Metabolism during Exercise

“…Cellular oxygen availability can be assessed in muscle of contrasting fiber types with phosphorescence quenching 9 or in intact working muscle with either nearinfrared spectroscopy 28 or 1 H magnetic resonance spectroscopy. 36,60 However, these methods lack specificity when measuring the dynamics of cellular oxygen consumption in a large muscle group during exercise.…”