ACTIVATION RATE OF GLYCOGEN PHOSPHORYLASE AND PYRUVATE DEHYDROGENASE IN HUMAN SKELETAL MUSCLE DURING INTENSE EXERCISE 588

Abstract

The purpose of this study was to determine the time course for the transformation of glycogen phosphorylase and pyruvate dehydrogenase (PDH) during the first and third bouts of maximal intermittent exercise. Six subjects completed three 30-s bouts of maximal isokinetic cycling at 100 rpm, each separated by 4 min of rest. Biopsies of the vastus lateralis were taken before, and at 6s, 15s and 30s of bouts 1 and 3. Total work in bout 1 was 18.4±0.5 kJ, and decreased to 13.7±1.0 kJ in bout 3. Prior to bout 1, PDH was 14.2±0.1% activated, increased to 48.4±0.1% at 6s, and was totally activated by 15s. The mole fraction of active phosphorylase (PHOS a) was 9.9±2.2% at rest, increased to 46.8±5.3% and 47.4±6.4% at 6s and 15s, respectively, and by 30s, decreased to 21.8±4.2%. Prior to bout 3, PDH was 41.7±0.1% activated; by 6s it was 100% activated. PHOS a fraction increased from 10.5±2.7% to 14.7±2.7% and 20.5±1.6% at 6s and 15s, respectively, and was partially inactivated to 16.2±5.7% at 30s. Glycogen utilization was 127.0±35.1 and 15.1±10.2 mmol/kg dw in bouts 1 and 3, respectively. Lactate increased from 2.7±0.4 to 76.1±7.4 mmol/kg dw in bout 1 and from 97.7±16.7 to 107.1±15.3 mmol/kg dw in bout 3. In bout 1, the rapid transformation to PHOS a was associated with rapid increases in glycogenolysis and a large accumulation of lactate due to the delayed activation of PDH. However, in bout 3 the small change in PHOS a resulted in a lower rate of glycogenolysis and the rapid activation of PDH resulted in a greater oxidation of pyruvate and hence less lactate accumulation.