Oishi Y, Imoto K, Ogata T, Taniguchi K, Matsumoto H, Roy R R
Laboratory of Muscle Physiology, Faculty of Education, Kumamoto University, Kumamoto, Japan.
Acta Physiol Scand. 2002 Dec;176(4):311-8. doi: 10.1046/j.1365-201X.2002.01036.x.
Clenbuterol, a beta2-agonist, administration results in hypertrophy of fast fibres and an increase in the fast myosin heavy chain (MHC) composition of both fast and slow muscles. The present study was designed to determine the phenotypic response at the single fibre level. Clenbuterol was added to the drinking water (30 mg L(-1)) of adult male Wistar rats for 4 weeks. Single fibres from the soleus muscle of control (10 rats; 555 fibres) and clenbuterol-treated (10 rats; 577 fibres) were dissected and their MHC isoform composition was determined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis. Body, heart, and soleus weights were 9, 24, and 27% higher in clenbuterol-treated than control rats. The mean cross-sectional areas of fast and slow/fast hybrid fibres were approximately 64 and approximately 74% larger in the clenbuterol-treated than control rats, whereas the size of the slow fibres were similar in the two groups. Fibres from control soleus showed three MHC patterns: pure type I (84%), pure type IIa (4%), and type I + IIa (12%) MHC. Some fibres from clenbuterol-treated soleus showed a de novo expression of type IIx MHC resulting in the following fibre type proportions: pure type I (62%), pure type IIa (2%), type I + IIa (26%), type I + IIa + IIx (6%), and type IIa + IIx (1%). In those fibres containing multiple MHCs, there was a shift towards the faster MHC isoforms after clenbuterol treatment. These data indicate that clenbuterol results in muscle fibre hypertrophy, stimulates a de novo expression of type IIx MHC and increases the percentage of fibres containing multiple MHC isoforms in the rat soleus muscle. These phenotypic changes at the single fibre level are consistent with a clenbuterol-related shift in the functional properties of the soleus towards those observed in a faster muscle.
克伦特罗是一种β2 肾上腺素能激动剂，给药后会导致快肌纤维肥大，且快肌和慢肌中快肌球蛋白重链（MHC）的组成都会增加。本研究旨在确定单纤维水平的表型反应。将克伦特罗添加到成年雄性 Wistar 大鼠的饮用水中（30 mg L(-1)），持续 4 周。解剖对照大鼠（10 只；555 根纤维）和经克伦特罗处理的大鼠（10 只；577 根纤维）比目鱼肌的单根纤维，并用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析确定其 MHC 同工型组成。经克伦特罗处理的大鼠的体重、心脏重量和比目鱼肌重量比对照大鼠分别高 9%、24%和 27%。经克伦特罗处理的大鼠的快肌纤维和慢/快混合纤维的平均横截面积比对照大鼠分别大约大 64%和大约 74%，而两组慢肌纤维的大小相似。对照比目鱼肌的纤维呈现三种 MHC 模式：纯 I 型（84%）、纯 IIa 型（4%）和 I + IIa 型（12%）MHC。一些经克伦特罗处理的比目鱼肌纤维出现了 IIx MHC 的从头表达，导致以下纤维类型比例：纯 I 型（62%）、纯 IIa 型（2%）、I + IIa 型（26%）、I + IIa + IIx 型（6%）和 IIa + IIx 型（1%）。在那些含有多种 MHC 的纤维中，克伦特罗处理后向更快的 MHC 同工型转变。这些数据表明，克伦特罗会导致肌纤维肥大，刺激 IIx MHC 的从头表达，并增加大鼠比目鱼肌中含有多种 MHC 同工型的纤维百分比。单纤维水平的这些表型变化与比目鱼肌功能特性向更快肌肉中观察到的特性的克伦特罗相关转变一致。
