Table II

Quantitation of the Effects of Insulin and Muscle Contractions on GLUT4 Intracellular Depots

BasalInsulinContractionInsulin + contractions
LMAverage pixel  density around  nuclei*100.0 ± 5.7 (1/42)68.9 ± 4.1 (1/27)74.2 ± 4.5 (1/31)51.6 ± 3.7 (1/39)
EMTGN‡  67 ± 18(2/20)
 56 ± 14(2/13)
49 ± 2(2/14)
 36 ± 10(2/26)
EMSubsarcolemmal  cytoplasm§ 38.6 ± 7.134.3 ± 5.728.6 ± 2.915.7 ± 7.1
 I band 16.1 ± 0.0 9.1 ± 2.7 9.1 ± 1.6 5.4 ± 0.0
 A band  4.5 ± 0.3 2.4 ± 0.3 1.4 ± 0.7 0.9 ± 0.3
(2/402)(2/209)(2/288)(2/150)
  • Fibers from each of the four experimental groups were labeled with anti-GLUT4 antibody and processed for either immunofluorescence (LM) or immunogold electron microscopy (EM). All results are given as mean ± SEM. The numbers in parentheses represent the number of independent experiments followed by the number of organelles or vesicles counted. Since nonspecific labeling at the EM level in the absence of primary antibody only consists of mostly single grains (never more than two together) and the average size of the small GLUT4 depots consisted of on average eight grains, no background correction has been done on these data.  

  • *  Z series of confocal images at the surface of fibers were recorded at high magnification (refer to Materials and Methods). The average pixel density around nuclei (as shown in Fig. 9), using maximum projections, was calculated.  

  •  Number of grains associated with each identifiable stack of Golgi cisternae, primarily located in the TGN.  

  • §  Number of small GLUT4 depots per 100 μm2 in the subsarcolemmal cytoplasm (defined as the region between the plasma membrane and the myofibrils), and in the I and A bands.