Is the change in intracellular pH during fatigue large enough to be the main cause of fatigue?

1986 ◽  
Vol 64 (6) ◽  
pp. 764-767 ◽  
Author(s):  
J. M. Renaud ◽  
Y. Allard ◽  
G. W. Mainwood
Keyword(s):  
Intracellular Ph ◽  
Extracellular Ph ◽  
Sartorius Muscle ◽  
Bathing Solution ◽  
Tetanic Contraction ◽  
Tetanic Force ◽  
Fatigue Effect ◽  
Frog Sartorius Muscle ◽  
Stimulation Period ◽  
Frog Sartorius

The intracellular pH of frog sartorius muscles exposed to an extracellular pH 8.0 (25 mM HCO3−, 1% CO2) was 6.9–7.1. Following a fatiguing stimulation period (one tetanic contraction per second for 3 min), the intracellular pH was 6.5–6.7. When similar experiments were repeated with frog sartorius muscles exposed to pH 6.4 (2 mM HCO3−, 1% CO2), the intracellular pH was 6.8–6.9 at rest and 6.3–6.4 following fatigue. So, in both experiments the intracellular pH decreased by 0.4–0.5 pH unit during fatigue. When the CO2 concentration of the bathing solution was increased from 1 to 30%, the intracellular pH of resting muscles decreased from 7.0 to 6.2–6.3. Although the effect of CO2 on the intracellular pH was greater than the fatigue effect, the decrease in tetanic force with CO2 was less than 40%, while during fatigue the tetanic force decreased by at least 70%. Therefore in frog sartorius muscle the decrease in tetanic force during fatigue exceeds the decrease that is expected from just a change in intracellular pH.

Na+ and K+ effect on contractility of frog sartorius muscle: implication for the mechanism of fatigue

1995 ◽  
Vol 268 (6) ◽  
pp. C1528-C1536 ◽  
Author(s):  
R. Bouclin ◽  
E. Charbonneau ◽  
J. M. Renaud
Keyword(s):  
Sartorius Muscle ◽  
Combined Effects ◽  
Large Decrease ◽  
Tetanic Contraction ◽  
Muscle Contractility ◽  
Tetanic Force ◽  
Twitch Force ◽  
Individual Effects ◽  
K Concentration ◽  
Frog Sartorius

Although a decrease in extracellular Na+ and an increase in K+ concentration are believed to contribute to the decrease in force during fatigue, the force of unfatigued muscle decreases only with quite large changes in Na+ and K+ concentration. The objective of this study was to determine whether concomitant and smaller changes in Na+ and K+ concentration have greater effects on muscle contractility than individual changes. At 3 mM K+, a large decrease in Na+ from 120 to 60 mM had no effect on the twitch force, while the tetanic force decreased by 31.2%. At 120 mM Na+, an increase in K+ from 3 to 9 mM potentiated the twitch force by 41.1%, had no effect on the tetanic force at 7 mM, and decreased the tetanic force by 40.4% at 9 mM; both the twitch force and tetanic force were completely abolished at 11 mM K+. The potentiation of the twitch force between 3 and 9 mM K+ was less at 60, 80, and 100 mM than at 120 mM Na+. A reduction in Na+ concentration also reduced the K+ concentration at which the twitch force and tetanic force decreased and were completely abolished. It is shown that the combined effects of Na+ and K+ on the twitch and tetanic contractions were greater than the sum of their individual effects. Furthermore, it is proposed that neither Na+ nor K+ alone can be considered as an important factor in the decrease in force during fatigue, whereas together they are important for the tetanic contraction, but not for the twitch contraction.

The effects of pH on the kinetics of fatigue and recovery in frog sartorius muscle

1985 ◽  
Vol 63 (11) ◽  
pp. 1435-1443 ◽  
Author(s):  
J. M. Renaud ◽  
G. W. Mainwood
Keyword(s):  
Extracellular Ph ◽  
Sartorius Muscle ◽  
Frog Sartorius Muscle ◽  
Fatigue Development ◽  
Effects Of Ph ◽  
Force Recovery ◽  
Ph Dependent ◽  
Contraction Cycle ◽  
Kinetics Of ◽  
Frog Sartorius

The effects of pH on the kinetics of fatigue and recovery in frog sartorius muscle were studied to establish whether the pH to which muscles are exposed (extracellular pH) has an effect on both the rate of fatigue development and recovery from fatigue. When frog sartorius muscles were stimulated with short tetanic stimuli at rates varying from 0.2 to 2.0 trains/s, a time- and frequency-dependent decrease in force development was observed, but extracellular pH had comparatively little effect. The recovery of tetanic force was dependent on the extracellular pH. This effect was characterized by a rapid recovery in force at pH 8.0 and an inhibition of recovery at pH 6.4 even when force decreased by only 25% during stimulation. Even when muscles were fatigued at pH 8.0 the rate of force recovery was still very small at pH 6.4. A model is proposed in which a step of the contraction cycle changes from a normal to a fatigued state. The rate of this transition is a function of the stimulation frequency and not pH. The reverse transition, from a fatigued to normal state is pH dependent; i.e., it is inhibited by H+. Measurements of resting and action potentials show that extracellular pH influences these parameters in the fatigue state, but there is no evidence that these changes are directly responsible for the pH-dependent step in the reversal of fatigue.

Constancy of Axial Spacings in Frog Sartorius Muscle during Contraction

Nature ◽  
1965 ◽  
Vol 206 (4991) ◽  
pp. 1358-1358 ◽  
Author(s):  
H. E. HUXLEY ◽  
W. BROWN ◽  
K. C. HOLMES
Keyword(s):  
Sartorius Muscle ◽  
Frog Sartorius Muscle ◽  
Frog Sartorius
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