Testosterone and Ca2+ regulation in skeletal muscle.

The aim of this study was to examine the effect of testosterone treatment on the expression of dihydropyridine and ryanodine receptors in skeletal muscle of mouse. Furthermore, the effects of training, a method also known to elevate the plasma testosterone level, were studied and compared to the effects of pure testosterone administration. Male mice were either administered with testosterone or trained with treadmill. After 6 weeks, hindlimb muscles were excised and the expression of receptors was measured by Western blotting. Furthermore, the alterations in myosin heavy chain phenotypes were studied. In general, both training and testosterone administration induced changes in the expression of both receptors and in myosin heavy chain composition. In testosterone treated mice the expression of dihydropyridine receptor in extensor digitorum longus was higher compared to the control ones (38.9 %, p = 0.026). In soleus the expression was quite the contrary (- 27.3 %, p = 0.044), as was the case with ryanodine receptor (- 51.4 %, p = 0.012). The amount of ryanodine receptors was higher in rectus femoris (144.0 %, p = 0.044) and plantaris (48.1 %, p = 0.037) in testosterone treated mice. In trained mice, the expression of ryanodine receptor was significantly higher in gastrocnemius (27.6 %, p = 0.018), soleus (57.2 %, p = 0.025), plantaris (28.5 %, p = 0.009) and extensor digitorum longus (94.8 %, p = 0.009) than in the control ones. No differences were observed in the dihydropyridine receptor level. To conclude, training has a more important role in skeletal muscle adaptation compared to increased plasma testosterone level. However, in postural muscles both treatments have comparable effects.