Received March 8, 2007
Revised April 16, 2007
Accepted after revision April 16, 2007
Control of microvascular oxygen pressures during
recovery in rat fast-twitch muscle of differing
oxidative capacity
Paul - McDonough 1*,
Brad J Behnke 2,
Danielle J Padilla 3,
Timothy I Musch 3,
David C Poole 3
1 University of Texas-Arlington
2 University of West Virginia
3 Kansas State University
* To whom correspondence should be addressed. E-mail: mcdonough{at}uta.edu.
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Abstract |
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Whether the speed of recovery of microvascular O2
pressures (PmvO2) differs within muscles composed
primarily of Type II fibers with contrasting oxidative
capacity has not been determined. We tested the
hypothesis that, following contractions, the recovery of
PmvO2 would be slower in the white (WG; low oxidative
capacity) versus the mixed gastrocnemius (MG; moderately
high oxidative capacity). Radiolabelled microsphere and
phosphorescence quenching techniques were utilized to
measure muscle blood flow ( , and hence O2 delivery, )
and PmvO2 during contractions (1 Hz twitch) at low (LO,
2.5 V) and high (HI, 4.5 V) intensities in rat (n=15) MG
and WG muscle and during subsequent recovery. Following
LO, end-contraction PmvO2 was lower in WG (11.6±0.5
mmHg) than MG (16.2±0.6 mmHg; P<0.05) while, contrary to
our hypothesis, the initial rate of change in PmvO2
during recovery (dPo2/dt; MG: 0.11±0.01 mmHg/s and WG:
0.06±0.03 mmHg/s) and mean response time (MRT; MG:
110.3±5.1 mmHg/s & WG: 113.5±8.4s, P>0.05) were not
different. In contrast, end-contraction baseline PmvO2
was not different following HI (MG: 10.3±0.6 and WG:
9.2±0.6 mmHg; P>0.05) but, in agreement with our
hypothesis, dPo2/dt was slower (MG: 0.07±0.01 > WG:
0.03±0.003 mmHg/s; P<0.05) and MRT longer (WG:
180.8±4.5s > MG: 115.4±6.7s; P<0.05) in WG vs. MG
following HI. These data suggest that following high-
intensity, though submaximal, muscle contractions, PmvO2
recovers much faster in the more oxidative medial
gastrocnemius than in the less oxidative white
gastrocnemius.
