Abstract

The changes in ammonia (NH3) and amonia contents in human skeletal muscle during isometric exercise (2/3 maximal voluntary contraction force) to fatigue have been investigated. Biopsies from musculus quadriceps femoris were obtained ar rest, fatigue, and 1 and 4 min recovery. Muscle NH3 (n = 9) increased from 1.3 +/- 0.3 mmol/kg dry muscle (dm) at rest to 3.6 +/- 0.6 at fatigue and remained elevating during recovery, whereas the lactate increase after contraction decreased rapidly during recovery. Total adenine nucleotide (TAN) content decreased from 28.7 +/- 0.5 mmol/kg dm at rest to 25.1 +/- 0.6 at fatigue. Muscle glutamine did not change after contraction, whereas glutamate decreased, and alanine increased. In vivo AMP deaminase activity (measured by the rate of TAN decrease) was positively correlated with the percentage of fasttwitch fibers (r = 0.92; P < 0.001) and the ATP turnover rate (r = 0.75); P < 0.001) but was not related to the muscle lactate content (r = 0.27; P < 0.05). Phosphocreatine decreased to 6.1 +/- 0.7 mmol/kg dm (range = 1-11) after contraction. It is concluded that during exercise 1) activation of AMP deaminase in vivo occurs when a high ATP turnover rate is coupled with a low phosphocreatine level, 2) muscle pH is of minor importance for direct activation of AMP deaminase in vivo, and 3) increases in NH3 do not have an important influence on glycolysis. Verf.-Referat