Effects of short- and long-term swimming on myostatin expression in red and white gastrocnemius muscle and heart muscle of the rat.

Myostatin (MSTN) belongs to the transforming growth factor-β superfamily and is known to play an essential role in the regulation of skeletal muscle mass. In particular, it has been characterized as a potent negative skeletal muscle growth factor (McPherron et al. 1997), which inhibits satellite cells activation (McCroskery et al. 2003), myoblast proliferation (Thomas et al. 2000) and myogenic differentiation in vitro (Rios et al. 2002). The aim of this study was to test the hypothesis that swim training might differentially impact myostatin expression in skeletal muscles depending on fibre type composition and in cardiac muscle of the rat. MSTN expression was analyzed by Real time RT-PCR, electrophoresis and immuno-histochemistry in red and white gastrocnemius (RG,WG) of male Wistar rats in two exercise conditions: 1) two consecutive bouts of 3 hrs swimming (short term swimming), 2) intensive long term swimming training for 4 weeks. In control animals the MSTN mRNA basal levels was higher in the WG. Both short and long term swimming resulted in a reduction of MSTN mRNA contents in the active rats mainly in WG. No significant differences in MSTN protein expression were found in Western blot, whereas immuno-histochemistry showed that MSTN was detected in presumptive satellite cells of a few muscle fibres of the controls. After training the number of MSTN positive spots decreased significantly in the WG. MSTN mRNA contents in the cardiac muscle were also determined and found to increase in trained rats. In conclusion, decreased MSTN mRNA contents in response to exercise may be mainly attributed to changes in fast fibres and is accompanied by minor changes in protein expression.