RESUMEN
AIMS AND METHODS: We studied changes in the expression of myosin and sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) and in Ca2+ uptake and release rates by the SR in rat slow-twitch soleus muscles treated with thyroid hormone (3,5,3'-triiodo-l-thyronine, T3) for 1, 3, 7 and 21 days. RESULTS: The content of fast SR Ca2+-ATPase isoform SERCA1a protein significantly increased as early as 3 days of T3 treatment, while a rise in fast myosin heavy chain isoforms was found only 21 days after the onset of T3 administration. T3-induced slow-to-fast transitions were much less pronounced in myosin light chain than in myosin heavy chain. Moreover, in vitro measurements of SR Ca2+-handling capacity with indo-1 indicated that increases in uptake rate preceded those of release rate (7 vs. 21 days). CONCLUSION: These data suggest that changes in the myosin and SERCA expressions seem not to occur in a coordinated manner at the early stage of hyperthyroidism and that intervention with T3 may temporarily produce slow-twitch type I fibres which contain, in addition to slow SERCA2a isoform, the appreciable amounts of fast SERCA1a isoform. Moreover, it is speculated that some fibres in the hyperthyroid soleus muscles may temporarily acquire unique contractile properties distinct from normal fast and slow fibres.
Asunto(s)
Hipertiroidismo/metabolismo , Músculo Esquelético/metabolismo , Miosinas/metabolismo , Retículo Sarcoplasmático/metabolismo , Animales , Western Blotting/métodos , Peso Corporal , Calcio , ATPasas Transportadoras de Calcio/metabolismo , Electroforesis/métodos , Isomerismo , Masculino , Cadenas Pesadas de Miosina/metabolismo , Cadenas Ligeras de Miosina/metabolismo , Tamaño de los Órganos , Ratas , Ratas Wistar , Factores de Tiempo , Triyodotironina/administración & dosificaciónRESUMEN
The present study examined the effects of acute high-intensity exercise on Ca(2+) uptake and release rates and Ca(2+)-adenosine triphosphatase (ATPase) activity of the sarcoplasmic reticulum (SR) from the costal diaphragm. The rats were run on a treadmill at an estimated requirement of 100% of maximal O2 consumption until fatigued (average time to exhaustion: 4.79 min). Muscle lactate and inorganic phosphate after exercise were increased by 65% (P < 0.05) and 35% (P < 0.05), respectively. With exercise, Ca(2+) uptake and release, which were detected in homogenates using the Ca(2+) fluorescent dye indo-1, were decreased by 24% (P < 0.05) and 22% (P < 0.05), respectively. The reduction in Ca(2+) uptake was paralleled by decreased activity of SR Ca(2+)-ATPase in both the absence and presence of Ca(2+) ionophore. These findings demonstrate that, in the diaphragm as well as in the locomotor muscles that have been explored in previous studies, the attenuations of the SR function is brought about by acute high-intensity exercise. These changes in the SR of the diaphragm may contribute, at least in part, to deteriorations in exercise tolerance and work productivity resulting from repetitive physical activities.
Asunto(s)
Diafragma/fisiología , Condicionamiento Físico Animal/fisiología , Retículo Sarcoplasmático/fisiología , Animales , Calcio/metabolismo , ATPasas Transportadoras de Calcio/metabolismo , Glucógeno/análisis , Lactatos/análisis , Masculino , Fatiga Muscular/fisiología , Fosfatos/análisis , Ratas , Ratas WistarRESUMEN
This study examined the effects of acute high-intensity and moderate-intensity exercise on Ca2+-stimulated adenosine triphosphatase (ATPase) activity and the Ca2+ and ATP dependence of Ca2+-ATPase of the sarcoplasmic reticulum (SR) in the soleus muscle. The rats were run on 10% grade at 50 m min(-1) or 25 m min(-1) until fatigued (avg. time to exhaustion 2.8 and 87.7 min, respectively). The catalytic activities of SR Ca2+-ATPase were significantly depressed immediately after both types of exercise. Kinetic analyses demonstrated that the Ca2+ affinity of Ca2+-ATPase was elevated by both types of exercise adopted in the present investigation whereas the increase in the ATP affinity was brought about by only high-intensity exercise. These results suggest that exhaustive exercise may induce in slow-twitch muscle fibre the environmental changes, which adversely affect SR Ca2+-ATPase activity and can overcome the positive influence arising from the increase in the Ca2+ and/or ATP affinities of SR Ca2+-ATPase.