The Metabolic Changes in Frog Sartorius Muscles During Recovery from Fatigue at Different External Bicarbonate Concentrations

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Abstract
Superfused sartorius muscles were stimulated to fatigue in either high (25 mequiv/l) or low (1 mequiv/l) bicarbonate solution. The fatigued muscles in both groups showed a loss of about 16 μmol/g wet weight of creatine phosphate (CP) and an increase in lactate of about 20 μmol/g. The small decrease in the mean ATP levels in both groups was not statistically significant. During recovery the rate of loss of lactate from the low bicarbonate group was much slower than from the high bicarbonate group. The initial rate of lactate loss by diffusion was more than twice as fast in the high bicarbonate group. Marked differences were also found in the glucose 6-phosphate level, which was higher, and the CP/creatine ratio which was lower in the low bicarbonate group. The differences between the isometric tension recovery curves and the curious shape of the tension recovery which showed a secondary dip about 15 min after the end of fatigue are interpreted in the light of the measured metabolic changes. It is postulated that intracellular hydrogen ion balance is a critical factor in the recovery process and that external bicarbonate modulates intracellular hydrogen ion balance and at the same time limits the efflux of lactate from the muscle.

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