Low cell pH depresses peak power in rat skeletal muscle fibres at both 30°C and 15°C: implications for muscle fatigue
Historically, an increase in intracellular H + (decrease in cell pH) was thought to contribute to muscle fatigue by direct inhibition of the cross-bridge leading to a reduction in velocity and force. More recently, due to the observation that the effects were less at temperatures closer to those obs...
Saved in:
Published in | The Journal of physiology Vol. 575; no. 3; p. 887 |
---|---|
Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
The Physiological Society
15.09.2006
|
Online Access | Get full text |
Cover
Loading…
Summary: | Historically, an increase in intracellular H + (decrease in cell pH) was thought to contribute to muscle fatigue by direct inhibition of the cross-bridge leading to a reduction
in velocity and force. More recently, due to the observation that the effects were less at temperatures closer to those observed
in vivo , the importance of H + as a fatigue agent has been questioned. The purpose of this work was to re-evaluate the role of H + in muscle fatigue by studying the effect of low pH (6.2) on force, velocity and peak power in rat fast- and slow-twitch muscle
fibres at 15°C and 30°C. Skinned fast type IIa and slow type I fibres were prepared from the gastrocnemius and soleus, respectively,
mounted between a force transducer and position motor, and studied at 15°C and 30°C and pH 7.0 and 6.2, and fibre force ( P 0 ), unloaded shortening velocity ( V 0 ), forceâvelocity, and forceâpower relationships determined. Consistent with previous observations, low pH depressed the P 0 of both fast and slow fibres, less at 30°C (4â12%) than at 15°C (30%). However, the low pH-induced depressions in slow type
I fibre V 0 and peak power were both significantly greater at 30°C (25%
versus 9% for V 0 and 34%
versus 17% for peak power). For the fast type IIa fibre type, the inhibitory effect of low pH on V 0 was unaltered by temperature, while for peak power the inhibition was reduced at 30°C (37%
versus 18%). The curvature of the forceâvelocity relationship was temperature sensitive, and showed a higher a / P 0 ratio (less curvature) at 30°C. Importantly, at 30°C low pH significantly depressed the ratio of the slow type I fibre, leading
to less force and velocity at peak power. These data demonstrate that the direct effect of low pH on peak power in both slow-
and fast-twitch fibres at near- in vivo temperatures (30°C) is greater than would be predicted based on changes in P 0 , and that the fatigue-inducing effects of low pH on cross-bridge function are still substantial and important at temperatures
approaching those observed in vivo . |
---|---|
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2006.106732 |