Carnosine and taurine contents of type I, IIA and IIB fibres in the middle gluteal muscle

Authors


Department of Physiology, The Animal Health Trust, Snailwell Road, Newmarket, Suffolk CB8 7DW, UK.

Summary

Thoroughbred racing involves periods of intense exercise above the anaerobic threshold, characterised by H+ ion accumulation in muscle. Progressive intracellular acidosis may be a primary cause of local muscle fatigue. Carnosine is quantitatively the most important buffer in equine skeletal muscle with estimated contents 3–5-fold greater in type II compared with type I fibres. Taurine is believed to be concentrated in type I fibres. In the present study we have measured carnosine and taurine contents directly within individual fibres. Seven samples were collected from the middle gluteal muscle of 5 horses at post mortem. Fibres were dissected from freeze-dried tissue, weighed and characterised as types I, IIA or IIB by histochemistry. Carnosine and taurine contents were determined by HPLC. Mean (± s.d.) carnosine contents of type I, IIA and IIB fibres were 24.9 ± 4.4 mmol/kg dry muscle (d.m.), 94.8 ± 6.8 mmol/kg d.m. and 104.3 ± 11.9 mmol/kg d.m. respectively. Mean (± s.d.) taurine contents of type I, IIA and IIB fibres were 54.3 ± 8.3 mmol/kg d.m., 2.8 ± 2.1 mmol/kg d.m. and 1.8 ± 1.9 mmol/kg d.m. respectively. The results agree with previous estimates. Higher carnosine contents in type II fibres emphasise the importance of carnosine to intramuscular acid-base regulation. A specific role for taurine in type I fibres is unclear. Owing to the differential distribution in muscle fibres of carnosine and taurine, their appearance in plasma may be useful in diagnosing types I or II fibre damage.

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