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Control of microvascular oxygen pressures during recovery in rat fast‐twitch muscle of differing oxidative capacity
Author(s) -
McDonough Paul,
Behnke Brad J.,
Padilla Danielle J.,
Musch Timothy I.,
Poole David C.
Publication year - 2007
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2007.037721
Subject(s) - chemistry , contraction (grammar) , oxidative phosphorylation , anatomy , medicine , biochemistry , biology
Whether the speed of recovery of microvascular O 2 pressures () differs within muscles composed primarily of type II fibres with contrasting oxidative capacity has not been determined. We tested the hypothesis that, following contractions, the recovery of would be slower in the white (WG; low oxidative capacity) versus the mixed gastrocnemius (MG; comparatively high oxidative capacity). Radiolabelled microsphere and phosphorescence quenching techniques were used to measure muscle blood flow (, hence O 2 delivery, ) and during contractions (1 Hz twitch) at low (LO, 2.5 V) and high intensities (HI, 4.5 V) in rat ( n = 15) MG and WG muscle and during subsequent recovery. Following the LO protocol, end‐contraction was lower in WG (11.6 ± 0.5 mmHg) than in MG (16.2 ± 0.6 mmHg; P < 0.05) while, contrary to our hypothesis, the initial rate of change in during recovery (/d t ; MG 0.11 ± 0.01 mmHg s −1 and WG 0.06 ± 0.03 mmHg s −1 ) and mean response time (MRT; MG 110.3 ± 5.1 s and WG 113.5 ± 8.4 s, P > 0.05) were not different. In contrast, end‐contraction baseline was not different following the HI protocol (MG 10.3 ± 0.6 mmHg and WG 9.2 ± 0.6 mmHg; P > 0.05) but, in agreement with our hypothesis, /d t was slower (MG 0.07 ± 0.01 mmHg s −1 and WG 0.03 ± 0.003 mmHg s −1 ; P < 0.05) and MRT longer (WG 180.8 ± 4.5 s and MG 115.4 ± 6.7 s; P < 0.05) in WG versus MG following the HI protocol. These data suggest that following high‐intensity, though submaximal, muscle contractions, recovers much faster in the more oxidative mixed gastrocnemius than in the less oxidative white gastrocnemius.