The purpose of this study was to determine whether myostatin alters glucose transporter-4 (GLUT4) expression in bovine skeletal muscles and myoblasts isolated from double-muscled (DM) and normal-muscled (NM) Japanese Shorthorn cattle. Plasma concentrations of glucose were lower in DM cattle than in NM cattle (P < 0.01). The expression of GLUT4 messenger RNA (mRNA) in the skeletal muscle exvivo and in myoblasts at 72h after differentiation invitro was higher in DM cattle than in NM cattle (P < 0.01). In contrast, the NM and DM cattle did not differ with respect to skeletal muscle expression of GLUT1 and myocyte enhancer factor-2c (MEF2c), a transcription factor of GLUT4. In differentiated myoblasts, the expression of GLUT1, GLUT4, and MEF2c mRNAs was greater in DM cattle than in NM cattle (P < 0.01). In the presence and absence of insulin, glucose uptake in myoblasts was increased in DM cattle relative to that of NM cattle (P < 0.01). The addition of myostatin decreased the expression of GLUT4 and MEF2c mRNAs in DM myoblasts (P < 0.05). Results of the present study suggest that myostatin inhibits the expression of GLUT4 mRNA possibly via MEF2c and that the greater ability of the DM cattle to produce muscle relative to the NM cattle may be due to their greater sensitivity to insulin and greater use of glucose.
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