Prolonged treatment with the β2-adrenoceptor agonist clenbuterol (1-2 mg·kg body mass-1·day -1) is known to induce the hypertrophy of fast-contracting fibers and the conversion of slow- to fast-contracting fibers. We investigated the effects of administering a lower dose of clenbuterol (250 μg·kg body mass-1·day -1) on skeletal muscle myosin heavy chain (MyHC) protein isoform content and adenine nucleotide (ATP, ADP, and AMP) concentrations. Male Wistar rats were administered clenbuterol (n = 8) or saline (n = 6) subcutaneously for 8 wk, after which the extensor digitorum longus (EDL) and soleus muscles were removed. We demonstrated an increase of type IIa MyHC protein content in the soleus from ~0.5% in controls to ~18% after clenbuterol treatment (P < 0.05), which was accompanied by an increase in the total adenine nucleotide pool (TAN; ~19%, P < 0.05) and energy charge [E-C = (ATP + 0.5 ADP)/(ATP + ADP + AMP); ~4%; P < 0.05]. In the EDL, a reduction in the content of the less prevalent type I MyHC protein from ~3% in controls to 0% after clenbuterol treatment (P < 0.05) occurred without any alterations in TAN and E-C. These findings demonstrate that the phenotypic changes previously observed in slow muscle after clenbuterol administration at 1-2 mg·kg body mass-1·day-1 are also observed at a substantially lower dose and are paralleled by concomitant changes in cellular energy metabolism.
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|Issue number||3 48-3|
|Publication status||Published - 2000|
- β-Adrenoceptor agonist
- Adenosine 5'-triphosphate
- Energy charge
- Myosin heavy chain protein composition