Rats were infused with saline (open symbols) or insulin (10 milliunits/min/kg) (filled symbols), while clamping blood glucose at 5 mM. This required infusing glucose at 2.9 ± 0.75 and 142 ± 4 μmol/min/kg in the control and insulin-treated animals, respectively. After 2 h, the rectus abdominus muscle was freeze-clamped in situ. Hind limb glucose uptake measured over this time was increased from 0.20 ± 0.4 to 0.52 ± 0.13 μmol/min by insulin. Single fibers were dissected from three control and three insulin-stimulated muscles. LDH and MDH activities were measured in individual fibers. Based on these activities the fibers were divided into the following three categories: Type I, Type IIA/D, and Type IIB fibers, identified as described by Hintz et al. (12). This strategy does not distinguish between IIA and IID fibers, so these fibers are grouped together. The mean (± S.E.) LDH activities (in mmol/hr/kg, dry weight) in the control and insulin-treatment groups, respectively, were as follows: Type I, 18.7 ± 2.2 and 20.2 ± 1.1; Type IIA/D, 44.1 ± 2.9 and 47.2 ± 3.0; Type IIB, 81.6 ± 1.6 and 80.0 ± 1.8. MDH activities were as follows: Type I, 12.0 ± 0.9 and 12.8 ± 0.4; Type IIA/D, 18.4 ± 0.5 and 19.0 ± 0.5; and Type IIB, 3.7 ± 0.2 and 3.5 ± 0.2.

Tibialis anterior (TA), EDL, gastrocnemius (Gastroc.), and soleus muscles were dissected from two lines of mice, PPL-1 and PPL-2, expressing the UDP-Glc PPL transgene and from wild type littermates. UDP-Glc PPL activity was measured in extracts of these muscles and expressed relative to extract protein.

Glycogen and UDP-Glc were measured in samples of quadricep muscles from PPL-1 mice and nontransgenic littermates. The results are expressed relative to wet weight of the tissues and are the mean values ± S.E. of measurements obtained from muscles of three wild type mice and four transgenic mice.

Muscles from PPL-1 mice and nontransgenic littermates were incubated for 30 min at 37 °C without or with either 100 microunits/ml insulin (A) or 250 milliunits/ml insulin (B and C) in Krebs-Ringer bicarbonate buffer containing 5 mM [U-¹⁴C]glucose (500 cpm/nmol). [U-¹⁴C]Glucose incorporation into glycogen was determined and expressed relative to the wet weight of the tissues. Mean values ± S.E. from eight wild type and eight transgenic EDL muscles (A), four wild type and four transgenic EDL muscles (B), and three wild type and three transgenic hemidiaphragms (C) are presented.

Levels of glycogen in equivalents of glucose (A) and UDP-Glc (B) were measured in single muscle fibers, which were divided into the fiber type categories described in the legend to Fig. 1. Mean values ± S.E. (where n = number of fibers) are presented. The significance of differences between insulin and control values were evaluated by a two-tailed heteroscedastic t test (36). *, not significantly different; **, p <0.01; ***, p <0.001.

Quadricep, EDL, and diaphragm muscles were dissected from two PPL-1 mice and from two nontransgenic littermates. Samples of extracts were subjected to SDS-PAGE and immunoblotted with antibodies to UDP-Glc PPL.

PPL-1 mice (•) and nontransgenic littermates (○) were fasted overnight. A, blood glucose was measured at increasing times after injecting glucose (1 mg/g of body weight) intraperitoneally. Mean values ± S.E. from 27 wild type mice and 33 trans-genic mice are presented. B, blood glucose was measured at increasing times after injecting glucose (0.5 mg/g of body weight) intravenously. Mean values ± S.E. from 28 wild type and 34 transgenic mice are presented.