Background
While ryanodine receptor 1 (RyR1) critically contributes to skeletal muscle contraction abilities by mediating Ca²⁺ion oscillation between sarcoplasmatic and myofibrillar compartments, AMP-activated protein kinase (AMPK) senses contraction-induced energetic stress by phosphorylation at Thr¹&sup7;². Phosphorylation of RyR1 at serine²&sup8;&sup4;³ (pRyR1Ser²&sup8;&sup4;³)
Conclusion
Resistance exercise induces acutely increased pRyR1Ser²&sup8;&sup4;³ and concomitantly pAMPKThr¹&sup7;² levels for up to 30 min in resistance exercised myofibers. This provides a time-course by which pRyR1Ser²&sup8;&sup4;³ can mechanistically impact Ca²⁺handling properties and consequently induce reduced myofiber contractility beyond immediate fatiguing mechanisms.
Methods
7 male subjects (age 23±2 years, height: 185±7 cm, weight: 82±5 kg) performed 3 sets of 8 repetitions of maximum eccentric knee extensions. Muscle biopsies were taken at rest, 15, 30 and 60 min post exercise. pRyR1Ser²&sup8;&sup4;³ and pAMPKThr¹&sup7;² levels were determined by western blot and semi-quantitative immunohistochemistry techniques.
Purpose
Determine the effects and early time-course of resistance exercise on pRyR1Ser²&sup8;&sup4;³ and pAMPKThr¹&sup7;² in type I and II myofibers.
Results
While total RyR1 and total AMPK levels remained unchanged, RyR1 was significantly more abundant in type II than type I myofibers. pRyR1Ser²&sup8;&sup4;³ increased 15 min and peaked 30 min (p<0.01) post exercise in both myofiber types. Type I fibers showed relatively higher increases in pRyR1Ser²&sup8;&sup4;³ levels than type II myofibers and remained elevated up to 60 min post resistance exercise (p<0.05). pAMPKThr¹&sup7;² also increased 15 to 30 min post exercise (p<0.01) in type I and II myofibers and in whole skeletal muscle.