Abstract
Skeletal muscles are an important reservoir of nitric oxide (NO•) stored in the form of nitrite [NO2−] and nitrate [NO3−] (NOx). Nitrite, which can be reduced to NO• under hypoxic and acidotic conditions, is considered a physiologically relevant, direct source of bioactive NO•. The aim of the present study was to determine the basal levels of NOx in striated muscles (including rat heart and locomotory muscles) with varied contents of tissue nitrite reductases, such as myoglobin and mitochondrial electron transport chain proteins (ETC-proteins). Muscle NOx was determined using a high-performance liquid chromatography-based method. Muscle proteins were evaluated using western-immunoblotting. We found that oxidative muscles with a higher content of ETC-proteins and myoglobin (such as the heart and slow-twitch locomotory muscles) have lower [NO2−] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO3−]. Our results demonstrated that fast-twitch muscles possess greater potential to generate NO• via nitrite reduction than slow-twitch muscles and the heart. This property might be of special importance for fast skeletal muscles during strenuous exercise and/or hypoxia since it might support muscle blood flow via additional NO• provision (acidic/hypoxic vasodilation) and delay muscle fatigue.
Highlights
Nitric oxide (NO) is a small, free radical and highly diffusible signalling molecule that at physiological concentrations regulates vascular tone and exerts positive effects on neurotransmission, cell apoptosis, gene expression and immune response [1]
The main finding of the present study was that the nitrite concentration in skeletal muscles differs between the various slow- and fast-twitch muscle types, whereas nitrate concentration did not significantly differ
We demonstrated for the first time that [NO2−] is lower in rat striated muscles–such as heart ventricles and soleus, which possess a higher electron transport chain (ETC) protein content and a higher myoglobin level
Summary
Nitric oxide (NO) is a small, free radical and highly diffusible signalling molecule that at physiological concentrations (pM/nM) regulates vascular tone and exerts positive effects on neurotransmission, cell apoptosis, gene expression and immune response [1].
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