EFFECTS OF THYROID HORMONE ON SARCOPLASMIC RETICULUM Ca2+ UPTAKE AND CONTRACTILE PROPERTIES IN RAT SOLEUS MUSCLE
- VernacularTitle:甲状腺ホルモンがラットヒラメ筋における筋小胞体のＣａ｀２＋´取り込みおよび収縮特性に及ぼす影響
- Author:
TAKASHI YAMADA
;
MASANOBU WADA
- Publication Type:Journal Article
- Keywords:
hyperthyroidism;
contractile property;
sarcoplasmic reticulum;
Ca2+ uptake rate;
relaxation
- From:Japanese Journal of Physical Fitness and Sports Medicine
2004;53(5):509-517
- CountryJapan
- Language:Japanese
-
Abstract:
The effect of hyperthyroidism on the contractile properties and Ca2+ sequestering abilities by the sarcoplasmic reticulum (SR) in the soleus muscles was examined in rats treated with thyroid hormone (3, 5, 3'-triiodo-L-thyronine, T3) (300μg/kg body weight) for 3, 7 and 21 days. At the end of a given treatment period, the right or left soleus muscle was mounted isometrically at 30°C, and stimulated directly using supramaximal current intensity. A twitch contraction was elicited by a 1 msec square-wave pulse and a tetanic contraction by 20 Hz stimulation for 600 msec. To evaluate fatigue resistance, muscles were stimulated at 40 Hz for 350 msec with tetani repeated at an interval of 2 sec during a 4-min period. Another soleus muscle was used, for analysis of SR Ca2+ -uptake rate and SR Ca2+ -ATPase activity. Pronounced increases in SR Ca2+ -uptake rate and ATPase activity were observed after T3 treatment periods longer than 6 days. These alterations were accompanied by decreases in twitch and tetanic tension, half-relaxation time, and fatigue resistance. The T3-treated muscles stimulated at 20 Hz relaxed during the interval between successive stimuli, indicating that the mechanical fusion of tetanic contractions was incomplete. SR Ca2+ uptake rate was significantly correlated both to tetanic tension and to fatigue resistance. These data suggest that there may be a causal relationship between changes in SR Ca2+ uptake and the loss of muscular strength in the hyperthyroid soleus.
