Control of microvascular oxygen pressures in rat muscles comprised of different fibre types

J Physiol. 2005 Mar 15;563(Pt 3):903-13. doi: 10.1113/jphysiol.2004.079533. Epub 2005 Jan 6.


In response to an elevated metabolic rate ((.-)V(O(2)), increased microvascular blood-muscle O(2) flux is the product of both augmented O(2) delivery ((.-)Q(O(2)), and fractional O(2) extraction. Whole body and exercising limb measurements demonstrate that (.-)Q(O(2) and fractional O(2) extraction increase as linear and hyperbolic functions, respectively, of (.-)V(O(2). Given the presence of disparate vascular control mechanisms among different muscle fibre types, we tested the hypothesis that, in response to muscle contractions, (.-)Q(O(2) would be lower and fractional O(2) extraction (as assessed via microvascular O(2) pressure, P(mvO(2))) higher in fast- versus slow-twitch muscles. Radiolabelled microsphere and phosphorescence quenching techniques were used to measure (.-)Q(O(2) and P(mvO(2)), respectively at rest and across the transition to 1 Hz twitch contractions at low (Lo, 2.5 V) and high intensities (Hi, 4.5 V) in rat (n = 20) soleus (Sol, slow-twitch, type I), mixed gastrocnemius (MG, fast-twitch, type IIa) and white gastrocnemius (WG, fast-twitch, type IIb) muscle. At rest and for Lo and Hi (steady-state values) transitions, P(mvO(2)) was lower (all P < 0.05) in MG (mmHg: rest, 22.5 +/- 1.0; Lo, 15.3 +/- 1.3; Hi, 10.2 +/- 1.6) and WG (mmHg: rest, 19.0 +/- 1.3; Lo, 12.2 +/- 1.1; Hi, 9.9 +/- 1.1) than in Sol (rest, 33.1 +/- 3.2 mmHg; Lo, 19.0 +/- 2.3 mmHg; Hi, 18.7 +/- 1.8 mmHg), despite lower (.-)V(O(2) and (.-)Q(O(2) in MG and WG under each set of conditions. These data suggest that during submaximal metabolic rates, the relationship between (.-)Q(O(2) and O(2) extraction is dependent on fibre type (at least in the muscles studied herein), such that muscles comprised of fast-twitch fibres display a greater fractional O(2) extraction (i.e. lower P(mvO(2))) than their slow-twitch counterparts. These results also indicate that the greater sustained P(mvO(2)) in Sol may be important for ensuring high blood-myocyte O(2) flux and therefore a greater oxidative contribution to energetic requirements.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Blood Flow Velocity / physiology
  • Female
  • Microcirculation / physiology*
  • Muscle Contraction / physiology*
  • Muscle Fibers, Skeletal / physiology*
  • Muscle, Skeletal / blood supply*
  • Muscle, Skeletal / physiology*
  • Oxygen / blood*
  • Oxygen Consumption / physiology*
  • Physical Exertion / physiology*
  • Rats
  • Rats, Sprague-Dawley


  • Oxygen