Abstract
BackgroundWhile 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 Thr172. Phosphorylation of RyR1 at serine2843 (pRyR1Ser2843) results in leaky RyR1 channels and impaired Ca2+homeostasis. Because acute resistance exercise exerts decreased contraction performance in skeletal muscle, preceded by high rates of Ca2+-oscillation and energetic stress, intense myofiber contractions may induce increased RyR1 and AMPK phosphorylation. However, no data are available regarding the time-course and magnitude of early RyR1 and AMPK phosphorylation in human myofibers in response to acute resistance exercise.PurposeDetermine the effects and early time-course of resistance exercise on pRyR1Ser2843 and pAMPKThr172 in type I and II myofibers.Methods7 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. pRyR1Ser2843 and pAMPKThr172 levels were determined by western blot and semi-quantitative immunohistochemistry techniques.ResultsWhile total RyR1 and total AMPK levels remained unchanged, RyR1 was significantly more abundant in type II than type I myofibers. pRyR1Ser2843 increased 15 min and peaked 30 min (p<0.01) post exercise in both myofiber types. Type I fibers showed relatively higher increases in pRyR1Ser2843 levels than type II myofibers and remained elevated up to 60 min post resistance exercise (p<0.05). pAMPKThr172 also increased 15 to 30 min post exercise (p<0.01) in type I and II myofibers and in whole skeletal muscle.ConclusionResistance exercise induces acutely increased pRyR1Ser2843 and concomitantly pAMPKThr172 levels for up to 30 min in resistance exercised myofibers. This provides a time-course by which pRyR1Ser2843 can mechanistically impact Ca2+handling properties and consequently induce reduced myofiber contractility beyond immediate fatiguing mechanisms.
Highlights
Human skeletal muscle tissue represents the vital organ for human locomotion
Resistance exercise induces acutely increased pRyR1Ser2843 and concomitantly pAMPKThr172 levels for up to 30 min in resistance exercised myofibers. This provides a time-course by which pRyR1Ser2843 can mechanistically impact Ca2+handling properties and induce reduced myofiber contractility beyond immediate fatiguing mechanisms
The ryanodine receptor 1 (RyR1) channel complex is mainly involved in facilitating the accurate release of Ca2+from sarcoplasmic compartments into myofibrillar areas and triggers the important calcium oscillation that is required for continued myofiber contractions
Summary
Human skeletal muscle tissue represents the vital organ for human locomotion. As such, it exerts a high plasticity to adapt to various modes of exercise [1]. ATPdependent ion channels and myosin ATPase enzymes exert high rates of ATP turnover and, energetic stress [17] in contracting myofibers, which induces increased phosphorylation of AMP-activated protein kinase (AMPK). Because this emphasizes a contraction-induced effect, we further postulated that exercise-induced phosphorylation of RyR1 is accompanied by elevated pAMPKThr172 levels, indirectly indicating that increased pRyR1Ser2843 results from myofiber contractions. Because acute resistance exercise exerts decreased contraction performance in skeletal muscle, preceded by high rates of Ca2+-oscillation and energetic stress, intense myofiber contractions may induce increased RyR1 and AMPK phosphorylation. No data are available regarding the time-course and magnitude of early RyR1 and AMPK phosphorylation in human myofibers in response to acute resistance exercise.
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