Table I

Quantitation of the Effects of Insulin and Muscle Contractions on GLUT4 Labeling in the Surface Membrane

BasalInsulinContractionsInsulin + contractions
Plasma membrane*1.7 ± 0.312.6 ± 0.714.7 ± 6.023.1 ± 3.0
(5/1409 μm)(4/929 μm)(4/1473 μm)(5/1634 μm)
 Increase over basal× 1× 7× 9× 14
T tubules (longitudinally sectioned)‡0.6 ± 0.7 8.7 ± 0.613.5 ± 5.118.2 ± 3.8
(3/82/34 μm)(3/119/60 μm)(3/161/85 μm)(3/198/74 μm)
 Increase over basal× 1× 15× 23× 30
T tubules (cross-sectioned plus0.8 ± 0.719.4 ± 1.223.3 ± 6.433.4 ± 2.6
 longitudinally sectioned)§(5/1316)(4/1010)(4/1616)(5/1276)
 Increase over basal× 1× 24× 29× 42
  • Fibers from each of the four experimental groups were labeled with anti-GLUT4 and processed for immunogold electron microscopy. Silver-enhanced gold grains were counted from longitudinal sections. All results are given as means ± SEM. Numbers in parentheses represent the number of independent experiments counted, followed for rows 1 and 2 by the total length of membrane counted (in μm), and for rows 2 and 3 by the number of triads counted.  

  • *  Number of grains/10 μm of plasma membrane. The background labeling in the absence of primary antibody was 2.8 ± 0.2 grains/10 μm and has been subtracted from the presented data.  

  •  Number of grains/10 μm of longitudinally sectioned junctional T tubule membrane. The background labeling in the absence of primary antibody was 1.2 ± 0.7 grains/10 μm and has been subtracted from the presented data.  

  • §  Percent of junctional T tubules labeled, including both cross- and longitudinally sectioned T tubules. In the absence of primary antibody 1.4 ± 0.4% of all triads were labeled. This has been subtracted from the presented data. Cross-sectioned T tubules represent ∼85% of the total number of encountered T tubules.