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

• The role of reduced muscle pH in the development of skeletal muscle fatigue is unclear. This study investigated the effects of lowering skeletal muscle intracellular pH by exposure to 30% CO2on the number of isometric tetani needed to induce significant fatigue. Isolated single mouse muscle fibers were stimulated repetitively at intervals of 4–2.5 s by using 80-Hz, 400-ms tetani at 28°C in Tyrode solution bubbled with either 5 or 30% CO2. Stimulation continued until tetanic force had fallen to 40% of the initial value. Exposure to 30% CO2caused a significant fall in intracellular pH of ∼0.3 pH unit but did not cause any significant changes in initial peak tetanic force. During the course of repetitive stimulation, intracellular pH fell by ∼0.3 pH unit in both normal and acidified fibers. The number of tetani needed to reduce force to 40% of the initial value was not significantly different in 5 and 30% CO2Tyrode. The sole effect of acidosis was to reduce the rate of relaxation 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.

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