C group ( 0
C group ( 0.05), &significant difference from the resting muscle of the same group ( 0.05). in control. A decrease in EC-induced phosphorylation of p70S6K, RPS6 and RFC37 PS in the 7-day unloaded soleus treated with SAC inhibitor did not differ from that of the 7-day unloaded soleus without SAC blockade. The results of the study suggest that (i) HU results in a blunted anabolic response to a bout of EC, (ii) attenuation of mTORC1-signaling and PS in response to EC in unloaded soleus may be associated with inactivation of SAC. 0.05) after 7-day HS compared with the control animals. There was no significant difference between any groups in normalized P0, absolute tetanic tension was decreased after 7-day HS (Table 1). Table 1 Changes in rats body weight, soleus weight-to-body weight ratio and P0, and P0 normalized to muscle cross-sectional area following 1-, 3- and 7 days of hindlimb unloading. = 7/group. Ccontrol rats, 1HS, 3HS and 7HShindlimb unloading for 1, 3 and 7 days. The data were analyzed using one-way ANOVA with Tukey. Rat weight: the main effect of HS = 0.158784, soleus weight/rat weight ratio: the main effect of HS = 0.001586, P0: the main effect of HS = 0.002901, Po/CSA: the main effect of HS = 0.589732; *significant difference vs. C group, 0.05. 2.1.2. The Rate of Muscle Protein SynthesisThe rate of PS in the resting soleus muscles significantly decreased by approximately 40% ( 0.05) following 3- and 7 days of HS (Figure 1). A bout of EC of the isolated rat JAK2-IN-4 soleus resulted in a significant rise in PS vs. the resting muscle in the C, 3HS and 7HS groups (Figure 1). Open in a separate window Figure 1 The rate of protein synthesis in the eccentrically-contracted rat soleus muscles following hindlimb unloading (experiment 1). Values are means SEM, expressed relative (%) to the control resting muscle; = 7/group. Ccontrol rats, 1HS, 3HS and 7HShindlimb unloading for 1, 3 and 7 days. The data were analyzed using 2-way ANOVA with Tukey. The main effect of HS = 2.00459E-11, the main effect of EC = 2.74866E-08, interaction effect = 1.08513E-06; *significant difference vs. C group ( 0.05), &significant difference from the resting muscle of the same group ( 0.05). Black barsresting muscle, white barseccentrically-contracted muscle. However, the level of EC-induced PS increment in the 1HS, 3HS and 7HS groups JAK2-IN-4 was 81%, 77% and 64% lower ( 0.05), respectively, than that in the C group (Figure 3a). 2.1.3. Phosphorylation of Key Signaling Proteins Involved in the Regulation of Muscle Protein SynthesisIn the resting muscle, there was a significant 43% ( 0.05) decrease in p70S6K phosphorylation in the 7HS group compared to the resting control (Figure 2a). p70S6K (Thr389) was significantly phosphorylated in response to EC in all groups, however EC-induced p70S6K phosphorylation increment in the 3HS and 7HS groups was significantly decreased by 104 and 97% ( 0.05), respectively, vs. the C group (Figure 3b). 4E-BP1 (Thr37/46) phosphorylation was significantly decreased in all HS groups compared to the control group in resting muscles (Figure 2b). However, 4E-BP1 (Thr37/46) phosphorylation in response to EC was significantly lower in all groups, and the level of this decline did JAK2-IN-4 not differ between the groups (Figure 3c). In the resting isolated muscles of 3HS and 7HS, GSK-3 (Ser9) phosphorylation was 44 and 47% ( 0.05) less than that in the resting control muscle (Figure 2c). A bout of EC revealed a significant decrease in GSK-3 phosphorylation increment in the isolated soleus muscles taken from hindlimb-unloaded rats as compared to the control rats (Figure 3d). 7-day HS resulted in a significant 42% ( 0.05) decrease in p90RSK (T359 + S363) phosphorylation vs. the C group (Figure 2d) in resting soleus muscle. EC-induced increase in p90RSK phosphorylation was observed in the C group as well as in the 1HS and 7 HS groups, but this increased p90RSK phosphorylation was not statistically different among these groups (Figure 3e). Open in a separate window Figure 2 Phosphorylation status of the key anabolic signaling proteins in the eccentrically-contracted rat soleus muscles following hindlimb unloading (experiment 1). (a): p70S6K (Thr389) phosphorylation; (b): 4E-BP1 (Thr37/46) phosphorylation;.
