Muscle glycogen resynthesis, signalling and metabolic responses following acute exercise in exercise-trained pigs carrying thePRKAG3mutation

Abstract

Hampshire pigs carrying thePRKAG3mutation in the AMP-activated protein kinase (AMPK) γ3 subunit exhibit excessive skeletal muscle glycogen storage and an altered glycogen synthesis signalling response following exercise. AMPK plays an important role as a regulator of carbohydrate and fat metabolism in mammalian cells. Exercise-trained muscles are repeatedly exposed to glycogen degradation and resynthesis, to which the signalling pathways adapt. The aim of this study was to examine the effect of acute exercise on glycogen synthesis signalling pathways, and the levels of insulin and other substrates in blood in exercise-trained pigs with and without thePRKAG3mutation. After 5 weeks of training, pigs performed two standardized treadmill exercise tests, and skeletal muscle biopsies were obtained immediately after exercise and 3 h postexercise in the first test, and 6 h postexercise in the second test. ThePRKAG3mutation carriers had higher glycogen storage, and resynthesis of glycogen was faster after 3 h but not after 6 h of recovery. Alterations in the concentrations of insulin, glucose, lactate and free fatty acids after exercise did not differ between the genotypes. The carriers showed a lower expression of AMPK and increased phosphorylation of Akt Ser473 after exercise, compared with non-carriers. Acute exercise stimulated the phosphorylation of AS160 in both genotypes, and the phosphorylation of GSK3α Ser21 and ACC Ser79 in the non-carriers. In conclusion, exercise-trained pigs carrying thePRKAG3mutation show an altered Akt and AMPK signalling response to acute exercise, indicating that glucose metabolism is associated with faster resynthesis of muscle glycogen in this group. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.