| Summary |
Progress in elucidating the biochemical mechanisms that underlie insulin resistance has been limited by the lack of suitable tissue culture models. Considering stable cell lines, such as C₂C₁₂, demonstrate poor insulin response, primary cells represent an ideal model for studying fuel metabolism as muscle specific metabolic characteristics are retained. The purpose oft his study was to examine differences in insulin-stimulated glucose uptake in endurance trained and sedentary men and women in differentiated primary human skeletal muscle cell culture. Endurance trained and sedentary men (VO₂max 65.8 ± 2.2, n = 9 vs. 50.0 ± 2.0 (SE) n = 6) and women 43 .4 ± 1.7, n = 5 vs. 30.7 ± 0.8, n = S) had muscle biopsies taken oft he vastus lateralis. All participants had a body mass index (BMI) less than 25 kg/m² and a mean age (VO₂max of 22.6 ± 1.6 years. Twelve hour fasted blood samples were used to determine plasma insulin and glucose concentrations for an estimate of in-vivo insulin action. No differences in fasting blood values were observed. Myoblasts were isolated from skeletal muscle samples and maintained in a growth media until proliferation was complete (3-5 weeks). Following proliferation, serum and growth factors were reduced for 8-days to allow fusion and differentiation into myotubes. Glucose uptake was measured at varying insulin concentrations (basal, 0.1 nM, 1.0 nM, 10 nM, 100 nM and 1000 nM). Insulin exposure significantly (P<0.05) mediated glucose uptake at the 10 nM, 100 nM, and 1000 nM concentrations. The trained male group demonstrated approximately 41% higher (P<0.05) glucose uptake in the basal and insulin mediated state compared to the sedentary group. No differences were observed in glucose uptake for the female group. Based on these preliminary findings it appears that training induced adaptations that increase insulin responsiveness and possibly basal glucose uptake may be retained in culture. Supported by NIH Grant Dk 52999 |
