Single muscle fiber contractile properties in diabetic RAT muscle

Introduction: Diabetes is associated with accelerated loss of muscle mass and function. We compared the contractile properties of single muscle fibers in young rat soleus muscle of uncontrolled streptozotocin-induced diabetic animals (n = 10) and nondiabetic controls (n = 10). Methods: Single fiber maximal force, shortening velocity, and power were assessed during maximal activation with calcium using the slack test 4 weeks after induction. Myosin heavy chain expression was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Oxidized myosin levels were detected by analyzing protein carbonyls in muscle homogenates. All fibers expressed the type I myosin heavy chain isoform. Results: Diabetic rats had higher blood glucose (537 vs. 175 mg/dl; P < 0.001) and lower body weight (171 vs. 356 g; P < 0.001) than controls. Muscle fibers from diabetic rats showed smaller cross-sectional area (1128 vs. 1812 μm²), lower maximal force (258 vs. 492 μN), and reduced absolute power (182 vs. 388 μN FL/s) (all P < 0.0001). No differences were seen in shortening velocity, specific force or specific power. Myosin carbonylation was higher (P < 0.01) in diabetic rats. Conclusions: After 4 weeks of untreated diabetes, there are significant alterations in muscle at the level of isolated single fibers and myosin protein, although some contractile properties seem to be protected. Muscle Nerve, 2015 Muscle Nerve 53: 958–964, 2016