Effects of CO2-induced acidification on the fatigue resistance of single mouse muscle fibers at 28C

The role of reduced muscle pH in the development of skeletalmuscle fatigue is unclear. This study investigated the effects oflowering skeletal muscle intracellular pH by exposure to 30% CO₂ on the number of isometrictetani needed to induce significant fatigue. Isolated single mousemuscle fibers were stimulated repetitively at intervals of 4-2.5 sby using 80-Hz, 400-ms tetani at 28°C in Tyrode solution bubbledwith either 5 or 30%CO₂. Stimulation continued until tetanic force had fallen to 40% of the initial value.Exposure to 30% CO₂ caused asignificant fall in intracellular pH of ~0.3 pH unit but did notcause any significant changes in initial peak tetanic force. During thecourse of repetitive stimulation, intracellular pH fell by ~0.3 pHunit in both normal and acidified fibers. The number of tetani neededto reduce force to 40% of the initial value was not significantlydifferent in 5 and 30% CO₂Tyrode. The sole effect of acidosis was to reduce the rate ofrelaxation of force, especially in fatigued fibers. It is concluded that, at 28°C, acidosis per se does not accelerate the development of fatigue during repeated tetanic stimulation of isolated mouse skeletal muscle fibers.