RESUMO
This work was undertaken to provide further insight into the role of mammalian target of rapamycin complex 1 (mTORC1) in skeletal muscle regeneration, focusing on myofiber size recovery. Rats were treated or not with rapamycin, an mTORC1 inhibitor. Soleus muscles were then subjected to cryolesion and analyzed 1, 10, and 21 days later. A decrease in soleus myofiber cross-section area on post-cryolesion days 10 and 21 was accentuated by rapamycin, which was also effective in reducing protein synthesis in these freeze-injured muscles. The incidence of proliferating satellite cells during regeneration was unaltered by rapamycin, although immunolabeling for neonatal myosin heavy chain (MHC) was weaker in cryolesion+rapamycin muscles than in cryolesion-only muscles. In addition, the decline in tetanic contraction of freeze-injured muscles was accentuated by rapamycin. This study indicates that mTORC1 plays a key role in the recovery of muscle mass and the differentiation of regenerating myofibers, independently of necrosis and satellite cell proliferation mechanisms.
Assuntos
Fibras Musculares Esqueléticas/fisiologia , Serina-Treonina Quinases TOR/fisiologia , Animais , Antibióticos Antineoplásicos/farmacologia , Western Blotting , Diferenciação Celular/fisiologia , Proliferação de Células , Congelamento , Imuno-Histoquímica , Masculino , Contração Muscular/fisiologia , Proteínas Musculares/biossíntese , Cadeias Pesadas de Miosina/metabolismo , Tamanho do Órgão/fisiologia , Fosforilação , Ratos , Ratos Wistar , Regeneração/fisiologia , Proteínas Quinases S6 Ribossômicas/metabolismo , Sirolimo/farmacologiaRESUMO
Although atracurium is a widely used neuromuscular blocker, we still lack knowledge regarding some of its cellular mechanisms of action. Thus, similar to other clinically used blockers atracurium induces, both in vivo and in vitro, fade of the tetanic contraction. However, the cellular mechanisms underlying this tetanic fade have never been systematically studied. In the present work these mechanisms were investigated in vitro. A sciatic nerve extensor digitorum longus muscle preparation of the rat was used. A combination of myographical and electrophysiological techniques was employed. Indirect twitches were evoked at 0.1 Hz and tetanic contractions at 50 Hz. Trains of end-plate potentials were evoked at a frequency of 50 Hz. The electrophysiological variables used in the analysis of the trains of end-plate potentials were: peak amplitude of the first end-plate potential in the train, peak amplitude of plateau end-plate potentials in the train, tetanic run-down of the end-plate potentials' train, quantal content of first and plateau end-plate potentials in the train, quantal size. In the myographical study atracurium, at a concentration of 2.4 microM, induced a complete fade of the tetanic contraction while only slightly affected the twitch. In the electrophysiological study atracurium, at the same 2.4 microM concentration, significantly decreased the amplitude of both first end-plate potentials in the train (control: 14.4 mV; atracurium: 3.2 mV) and plateau end-plate potentials (control: 10.8 mV; atracurium: 2.4 mV) and reinforced the tetanic run-down of the train of end-plate potentials, evaluated as the percent loss in amplitude of plateau end-plate potentials compared to first end-plate potentials in the trains (control: 25.2%; atracurium: 33.2%). Atracurium also significantly decreased the quantal content of first end-plate potentials in the train (control: 231; atracurium: 68), the quantal content of plateau end-plate potentials (control: 159; atracurium: 42) and the quantal size (control: 0.119 mV; atracurium: 0.075 mV). In relative terms the decrease in quantal content was about twice as large as the decrease in quantal size. This indicates that the fade of the tetanic contraction induced by atracurium (2.4 microM) is due to both pre- and postsynaptic blocking effects, the presynaptic one being stronger.
Assuntos
Atracúrio/farmacologia , Contração Muscular/efeitos dos fármacos , Junção Neuromuscular/efeitos dos fármacos , Fármacos Neuromusculares não Despolarizantes/farmacologia , Animais , Eletrofisiologia , Feminino , Técnicas In Vitro , Masculino , Potenciais da Membrana/efeitos dos fármacos , Placa Motora/efeitos dos fármacos , Placa Motora/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/citologia , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/fisiologia , Junção Neuromuscular/citologia , Junção Neuromuscular/fisiologia , Ratos , Ratos Wistar , Nervo Isquiático/efeitos dos fármacos , Nervo Isquiático/fisiologiaRESUMO
Although atracurium is a widely used neuromuscular blocker, we still lack knowledge regarding some of its cellular mechanisms of action. Thus, similar to other clinically used blockers atracurium induces, both in vivo and in vitro, fade of the tetanic contraction. However, the cellular mechanisms underlying this tetanic fade have never been systematically studied. In the present work these mechanisms were investigated in vitro. A sciatic nerve extensor digitorum longus muscle preparation of the rat was used. A combination of myographical and electrophysiological techniques was employed. Indirect twitches were evoked at 0.1 Hz and tetanic contractions at 50 Hz. Trains of end-plate potentials were evoked at a frequency of 50 Hz. The electrophysiological variables used in the analysis of the trains of end-plate potentials were peak amplitude of the first end-plate potential in the train, peak amplitude of plateau end-plate potentials in the train, tetanic run-down of the end-plate potentials' train, quantal content of first and plateau end-plate potentials in the train, quantal size. In the myographical study atracurium, at a concentration of 2.4 microM, induced a complete fade of the tetanic contraction while only slightly affected the twitch. In the electrophysiological study atracurium, at the same 2.4 microM concentration, significantly decreased the amplitude of both first end-plate potentials in the train (control 14.4 mV; atracurium 3.2 mV) and plateau end-plate potentials (control 10.8 mV; atracurium 2.4 mV) and reinforced the tetanic run-down of the train of end-plate potentials, evaluated as the percent loss in amplitude of plateau end-plate potentials compared to first end-plate potentials in the trains (control 25.2%; atracurium 33.2%). Atracurium also significantly decreased the quantal content of first end-plate potentials in the train (control 231; atracurium 68), the quantal content of plateau end-plate potentials (control 159; atracurium 42) and the quantal size (control 0.119 mV; atracurium 0.075 mV). In relative terms the decrease in quantal content was about twice as large as the decrease in quantal size. This indicates that the fade of the tetanic contraction induced by atracurium (2.4 microM) is due to both pre- and postsynaptic blocking effects, the presynaptic one being stronger.