Nitrite Concentration in the Striated Muscles Is Reversely Related to Myoglobin and Mitochondrial Proteins Content in Rats.

Skeletal muscles are an important reservoir of nitric oxide (NO • ) stored in the form of nitrite [NO 2 - ] and nitrate [NO 3 - ] (NO x ). 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 NO x 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 NO x 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 [NO 2 - ] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO 3 - ]. 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.