Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis

• Published in: PloS one 2018-04, Vol.13 (4), p.e0195704-e0195704
• Main Authors: Kryściak, Katarzyna, Majerczak, Joanna, Kryściak, Jakub, Łochyński, Dawid, Kaczmarek, Dominik, Drzymała-Celichowska, Hanna, Krutki, Piotr, Gawedzka, Anna, Guzik, Magdalena, Korostynski, Michał, Szkutnik, Zbigniew, Pyza, Elżbieta, Jarmuszkiewicz, Wiesława, Zoladz, Jerzy A, Celichowski, Jan
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Aerobics; Analysis; Animals; Biochemistry; Biology and Life Sciences; Biosynthesis; Copy number; Deoxyribonucleic acid; DNA; DNA, Mitochondrial - metabolism; Dynamin; Electron transport; Electron transport chain; Electron Transport Chain Complex Proteins - metabolism; Enzymes; Exercise; Exercise Test; Fatigue; Fatigue strength; Gene Expression Regulation; GTP Phosphohydrolases - metabolism; Health aspects; Male; Medicine and Health Sciences; Membrane Proteins - metabolism; Metabolism; Metabolites; Mitochondria; Mitochondria - metabolism; Mitochondrial DNA; Mitochondrial Proteins - metabolism; Motor units; Muscle contraction; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle function; Muscle strength; Muscle, Skeletal - metabolism; Muscles; Musculoskeletal system; Neurobiology; Neurosciences; Organelle Biogenesis; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha - metabolism; Phosphorylation; Physical Conditioning, Animal - physiology; Physical education; Physical Endurance - physiology; Physical training; Physiology; Properties (attributes); Proteins; Random Allocation; Rats, Wistar; Rehabilitation; Research and Analysis Methods; RNA, Messenger - metabolism; Rodents; Running - physiology; Signaling; Training; Treadmills; Treadmills (Exercise equipment)
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0195704

This study aimed at investigating the effects of 2, 4 and 8 weeks of endurance training on the contractile properties of slow (S), fast fatigue resistant (FR) and fast fatigable (FF) motor units (MUs) in rat medial gastrocnemius (MG) in relation to the changes in muscle mitochondrial biogenesis. The properties of functionally isolated MUs were examined in vivo. Mitochondrial biogenesis was judged based on the changes in mitochondrial DNA copy number (mtDNA), the content of the electron transport chain (ETC) proteins and PGC-1α in the MG. Moreover, the markers of mitochondria remodeling mitofusins (Mfn1, Mfn2) and dynamin-like protein (Opa1) were studied using qPCR. A proportion of FR MUs increased from 37.9% to 50.8% and a proportion of FF units decreased from 44.7% to 26.6% after 8 weeks of training. The increased fatigue resistance, shortened twitch duration, and increased ability to potentiate force were found as early as after 2 weeks of endurance training, predominantly in FR MUs. Moreover, just after 2 weeks of the training an enhancement of the mitochondrial network remodeling was present as judged by an increase in expression of Mfn1, Opa1 and an increase in PGC-1α in the slow part of MG. Interestingly, no signs of intensification of mitochondrial biogenesis assessed by ETC proteins content and mtDNA in slow and fast parts of gastrocnemius were found at this stage of the training. Nevertheless, after 8 weeks of training an increase in the ETC protein content was observed, but mainly in the slow part of gastrocnemius. Concluding, the functional changes in MUs' contractile properties leading to the enhancement of muscle performance accompanied by an activation of signalling that controls the muscle mitochondrial network reorganisation and mitochondrial biogenesis belong to an early muscle adaptive responses that precede an increase in mitochondrial ETC protein content.