Quantitation of the Effects of Insulin and Muscle Contractions on GLUT4 Labeling in the Surface Membrane
| . | . | Basal . | . | Insulin . | . | Contractions . | . | Insulin + contractions . |
|---|---|---|---|---|---|---|---|---|
| Plasma membrane* | 1.7 ± 0.3 | 12.6 ± 0.7 | 14.7 ± 6.0 | 23.1 ± 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 ± 0.6 | 13.5 ± 5.1 | 18.2 ± 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 plus | 0.8 ± 0.7 | 19.4 ± 1.2 | 23.3 ± 6.4 | 33.4 ± 2.6 | ||||
| longitudinally sectioned)§ | (5/1316) | (4/1010) | (4/1616) | (5/1276) | ||||
| Increase over basal | × 1 | × 24 | × 29 | × 42 |
| . | . | Basal . | . | Insulin . | . | Contractions . | . | Insulin + contractions . |
|---|---|---|---|---|---|---|---|---|
| Plasma membrane* | 1.7 ± 0.3 | 12.6 ± 0.7 | 14.7 ± 6.0 | 23.1 ± 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 ± 0.6 | 13.5 ± 5.1 | 18.2 ± 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 plus | 0.8 ± 0.7 | 19.4 ± 1.2 | 23.3 ± 6.4 | 33.4 ± 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.