Insulin resistance is commonly developed in obesity and is a trait of the beginning stage of type 2 diabetes mellitus (DM). It is highly likely that the high plasma fatty acid levels provoke the condition in the obese and insulin resistant state of type 2 DM. Hence, the purpose of this study was to determine if a high concentration of palmitic acid causes insulin resistance and how ceramide content is regulated under the various conditions in the isolated rat soleus muscle. A submaximal insulin stimulus (100 ,aU/ml) increased 3-O-methylglucose transport by -2.7 fold over basal conditions in the soleus (1.90 ± 0.23 µmol•ml"1•hr-1 vs. 5.06 ± 0.38 µmol•ml-1•hr-1, respectively) (P < 0.05). Five hours of palmitic acid preincubation induced a significant decrease in insulin-stimulated glucose transport (3.49 ± 0.11 µmol•ml-1•hr-1) by -31 % (P < 0.05) compared with the control. By contrast, the addition of L-cycloserine, a serine palmitoyltransferase inhibitor, attenuated the palmitic acid response by -20% (4.19 ± 0.27 µmol•ml-1•hr-1) (P < 0.05). A 5 hr preincubation with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an adenosine analogue that increase AMP activated protein kinase, increased glucose transport (3.29 ± 0.1 µmol•ml-1•hr-1) (P < 0.05) compared with the control group. Moreover, regardless if palmitic acid or L-cycloserine were present, insulin-stimulated glucose uptake was normalized (5.30 ± 0.38 µmol•ml-1•hr-1 and 5.56 ± 0.16 µmol•ml"1•hr-1, respectively) after 5 hr AICAR preincubation. We next measured the ceramide content to investigate whether the reduced glucose uptake results from ceramide accumulation in the soleus. The total ceramide mass in the soleus was increased by -35% in palmitic acid-treated group compared with the control group (122.02 ± 2.07 pmol•mg-1 vs. 90.79 + 1.24 pmol•mg 1, respectively) (P<0.05). Both L-cycloserine and AICAR decreased palmitateinduced ceramide synthesis by -20% and -14%, respectively (97.15 + 2.5 pmol•mg-1 and 105.79 ± 1.94 pmol•mg-1, respectively) (P<0.05) compared with the palmitic acid-treated group. We also measured serine palmitoyltransferase (SPT) to determine if AICAR regulates ceramide synthesis by inhibiting SPT. Total SPT protein level increased by -27% (P<0.05) and SPT activity increased by -44% (P<0.05) compared with the control group. By contrast, after muscles were incubated with L-cycloserine for 5 hr, both SPT protein level and enzyme activity were decreased by -17% and -23%, respectively (P<0.05). In adition, 5 hr AICAR treatment blunted palimitic acid-induced SPT protein level and enzyme activity by 11% (P<0.05) and 20% (P<0.05), respectively, compared with the palmitic acid-treated group. In conclusion, these data suggest that short term exposure (5 hr) to high fatty acid levels appears to cause insulin resistance by increasing ceramide accumulation and that AMPK expression (AICAR treatment) can attenuate the problem by regulating SPT levels. / School of Physical Education, Sport, and Exercise Science

The aim of this research was to investigate myogenic (i.e. growth) and proteolytic (i.e. breakdown) gene expression (GE) in skeletal muscle of young and old women. Myogenic (MyoD, MRF4, Myf5, myogenin, myostatin) and proteolytic (Atrogin-1, MuRF-1, FOXO3A) genes were examined in the basal state and after resistance exercise (RE). Six old women (OW: 85 ± 1 y) and eight young women (YW: 23 ± 1) performed 3 x 10 knee extensions at 70% of 1-repetition-maximum. Muscle biopsies were obtained from the vastus lateralis (i.e. thigh) before and 4 hours after RE.In the basal state, OW expressed higher levels (p<0.05) of MyoD, MRF4, myf5, myogenin, myostatin, FOXO3A and MuRF-1 compared to YW. Fiber type specific GE analysis in the OW showed that slow-twitch muscle fibers (MHC I) expressed higher levels (p<0.05) of myogenin and Atrogin-1, compared to fast-twitch (MHC Ila) fibers. In response to RE both YW and OW increased (p<0.05) mRNA levels of MyoD and MRF4, while a decrease (p<0.05) was observed for myostatin. MuRF-1 mRNA increased (p<0.05) in both age groups, while there was an age-specific induction (p<0.05) of Atrogin-1 after RE. Fiber type specific GE after RE in the old women showed that MHC Ila fibers did not induce myogenic GE. Robust increases (p<0.05) in MyoD, MRF4, and myogenin were only observed in the MHC I fibers. Both fiber types decreased (p<0.05) myostatin, and increased Atrogin-1 with RE. MuRF-1 mRNA levels increased specifically in MHC Ila fibers. In summary, skeletal muscle of OW expresses higher levels of mRNA for most selected genes at rest. With RE, aging skeletal muscle retains the ability to induce myogenic GE, although exclusive to MHC I fibers. After RE, proteolytic GE induction is greater in OW and most pronounced in MHC Ila fibers. Collectively, these data suggest that an imbalance exists in the regulation of the myogenic and proteolytic program in aging skeletal muscle. This research also provides the first evidence of intrinsic molecular differences between MHC I and MHC Ila fibers in OW, and may, in part, explain the MHC Ila atrophy apparent in sarcopenic muscle. / School of Physical Education, Sport, and Exercise Science

The purpose of this study was to investigate whole muscle and single muscle fiber adaptations in old men (OM) and old women (OW) over 80 years of age in response to progressive resistance training (PRT). Six OM (82±1 y, 74±4 kg, BMI 25±1 kg•m-2) and six OW (85±1 y, 67±3 kg, BMI 27±1 kg•m-2) resistance trained the knee extensors (3 sets, 10 repetitions) at 70% one repetition maximum 3 d•wk-1 for 12 wks. Vastus lateralis muscle biopsies were obtained before and after the PRT program. Isolated muscle fibers were studied in vitro at 15°C for diameter (Dia), peak tension (Po), unloaded shortening velocity (Vo), and absolute peak power (Abs Pwr). With PRT, OM increased whole muscle strength (40±6%, p<0.05), with no change in whole muscle size. OW also increased whole muscle strength (26±6%, p<0.05) without a change in whole muscle size. No differences were observed in any of the single muscle fiber parameters among MHC I or MHC IIa muscle fibers from OM or OW. The novel finding of this study was that despite an increase in whole muscle strength there was no change in whole muscle size, single fiber diameter, or single fiber contractile function. Given that there was no change in muscle size or cellular function with PRT, the improvement in whole muscle strength point to neurological changes. These data suggest that the hypertrophic mechanisms that are typically apparent in humans with PRT are attenuated in individuals over 80 y. / School of Physical Education, Sport, and Exercise Science