Zusammenfassung

In mixed fibre type skeletal muscle transcapillary PO(2) gradients (PO(2)mv−PO(2)is; microvascular and interstitial, respectively) drive O(2) flux across the blood-myocyte interface where the greatest resistance to that O(2) flux resides. Herein we assessed a broad spectrum of fibre type and oxidative capacity rat muscles across the rest-to-contractions (1 Hz, 120 s) transient to test the novel hypotheses that: i) slow-twitch PO(2)is would be greater than fast-twitch, ii) muscles with greater oxidative capacity have greater PO(2)is than glycolytic counterparts, and iii) whether PO(2)mv−PO(2)is at rest is maintained during contractions across all muscle types. PO(2)mv and PO(2)is were determined via phosphorescence quenching in soleus (SOL; 91% type I+IIa fibres and CSa: ~21 μmol min(−1) g(−1)), peroneal (PER; 33% and ~20 μmol min(−1) g(−1)), mixed (MG; 9% and ~26 μmol min(−1) g(−1)) and white gastrocnemius (WG; 0% and ~8 μmol min(−1) g(−1)) across the rest-contractions transient. PO(2)mv was higher than PO(2)is in each muscle (~6–13 mmHg; p<0.05). SOL PO(2)is (area) was greater than the fast-twitch muscles during contractions (p<0.05). Oxidative muscles had greater PO(2)is (nadir) (9.4 ± 0.8, 7.4 ± 0.9, and 6.4 ± 0.4; SOL, PER, MG respectively) than WG (3.0 ± 0.3 mmHg, p<0.05). The magnitude of PO(2)mv−PO(2)is at rest decreased during contractions in MG only (~11 to 7 mmHg; Time × (PO(2)mv−PO(2)is) Interaction, p<0.05). These data support that, since transcapillary PO(2) gradients during contractions are maintained in all muscle types, increased O(2) flux must occur via enhanced intracapillary diffusing conductance, which is most extreme in highly oxidative fast-twitch muscle.