Blood flow and O2 extraction as a function of O2 uptake in muscles composed of different fiber types.
We examined how the greater vasodilatory capacity of slow--(ST) versus fast-twitch (FT) muscles impacts the relationship between blood flow (Q ) and O2 uptake (VO2) and, consequently, the O2 extraction (a-vO2 diff.)-to-VO2 relationship. Q was measured with radiolabelled microspheres, while VO2 was calculated by the Fick principle using measurements of microvascular O2 pressure (phosphorescence quenching) at rest, low--(2.5 V) and high-intensity contractions (4.5 V) for soleus (Sol; ST, n=5), mixed-gastrocnemius (MG; FT, n=7) and white-gastrocnemius (WG; FT, n=7). The slope of the Q-to-VO2 relationship (delta Q/delta VO2] ) was not different among muscles (Sol = 5.5 +/- 0.2, MG = 6.0 +/- 0.11 and WG = 5.8 +/- 0.06; P > 0.05). In contrast, the intercept was greater (P < 0.05) for Sol (16.3 +/- 2.7 ml min(-1) 100 g(-1)) versus MG and WG (in ml min(-1) 100 g(-1): 1.39 +/- 0.26 and 1.45 +/- 0.23, respectively; MG and WG, P > 0.05). In addition, the a-vO2 diff.-to-VO2] relationship for Sol was shifted rightward compared to MG and WG. These data suggest that the increase in Q for a given change in VO2 is similar for slow- and fast-twitch muscles, at least for the range of metabolic rates and muscles studied herein and that a-vO2 diff. differences result from the lower resting Q in FT muscles.
Ferreira
Leonardo F
LF
Clarenburg Research Laboratory, Department of Anatomy & Physiology, Kansas State University, Manhattan, KS 66506-5802, USA.
McDonough
Paul
P
Behnke
Brad J
BJ
Musch
Timothy I
TI
Poole
David C
DC
D000818:Animals; D005260:Female; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000502:physiology; D014664:Vasodilation / Q000502:physiology
D010100:Oxygen