Regulation of hexokinase II activity and expression in human muscle by moderate exercise

A single bout of exercise increases the rate of insulin-stimulated glucose uptake and metabolism in skeletal muscle. Exercise also increases insulin-stimulated glucose 6-phosphate in skeletal muscle, suggesting that exercise increases hexokinase activity. Within 3 h, exercise increases hexokinase II (HK II) mRNA and activity in skeletal muscle from rats. It is not known, however, if a single bout of moderate-intensity exercise increases HK II expression in humans. The present study was undertaken to answer this question. Six subjects had percutaneous biopsies of the vastus lateralis muscle before and 3 h after a single 3-h session of moderate-intensity aerobic (60% of maximal oxygen consumption) exercise. Glycogen synthase, HK I, and HK II activities as well as HK I and HK II mRNA content were determined from the muscle biopsy specimens. The fractional velocity of glycogen synthase was increased by 446 ± 84% after exercise (P < 0.005). Hexokinase II activity in the soluble fraction of the homogenates increased from 1.2 ± 0.4 to 4.5 ± 1.6 pmol · min^-1 · μg^-1 (P < 0.05) but was unchanged in the particulate fraction (4.3 ± 1.3 vs. 5.3 ± 1.5). HK I activity in neither the soluble nor particulate fraction changed after exercise. Relative to a 28S rRNA control signal, HK II mRNA increased from 0.091 ± 0.02 to 0.195 ± 0.037 (P < 0.05), whereas HK I mRNA was unchanged (0.414 ± 0.061 vs. 0.498 ± 0.134, P < 0.20). The increase in HK II activity after moderate exercise in healthy subjects could be one factor responsible for the enhanced rate of insulin-stimulated glucose uptake seen after exercise.