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

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.