Skeletal muscle sodium glucose co-transporters in older adults with type 2 diabetes undergoing resistance training

We examined the expression of the sodium-dependent glucose co-transporter system (hSGLT3) in skeletal muscle of Hispanic older adults with type 2 diabetes. Subjects (65±8 yr) were randomized to resistance training (3x/wk, n=13) or standard of care (controls, n=5) for 16 weeks. Skeletal muscle hSGLT3 and GLUT4 mRNA transcript levels were determined by real time RT-PCR. hSGLT3 transcripts increased by a factor of ten following resistance training compared to control subjects (0.10, P=0.03). There were no differences in GLUT4 mRNA expression levels between groups. Protein expression levels of these transporters were confirmed by immunohistochemistry and Western blotting. hSGLT3 after resistance exercise was found not to be co-localized with the nicotinic acetylcholine receptor. The change in hSGLT3 transcript levels in the vastus lateralis muscle was positively correlated with glucose uptake, as measured by the change in muscle glycogen stores (r=0.53, P=0.02); and with exercise intensity, as measured by the change in muscle strength (r=0.73, P=0.001). Group assignment was be the only independent predictor of hSGLT3 transcript levels, explaining 68% of its variability (P=0.01). Our data show that hSGLT3, but not GLTU4, expression was enhanced in skeletal muscle after 16 weeks of resistance training. This finding suggests that hSGLT3, an insulin-independent glucose transporter, is activated with exercise and it may play a significant role in glycemic control with muscle contraction. The hSGLT3 exact mechanism is not well understood and requires further investigation. However its functional significance regarding a reduction of glucose toxicity and improvement of insulin resistance is the subject of ongoing research.