Increased postexercise insulin sensitivity is accompanied by increased AS160 phosphorylation in slow-twitch soleus muscle

Abstract

A single bout of exercise can enhance insulin-stimulated glucose uptake in both fast-twitch (type II) and slow-twitch (type I) skeletal muscle for several hours postexercise. Akt substrate of 160 kDa (AS160) is most distal insulin signaling proteins that have been proposed to contribute to the postexercise enhancement of insulin action in fast-twitch muscle. In this study, we examined whether the postexercise increase in insulin action of glucose uptake in slow-twitch muscle is accompanied by increased phosphorylation of AS160 and its paralog TBC1D1. Male Wistar rats (~1-month-old) were exercised on a treadmill for 180 min (9 m/min). Insulin (50 μU/mL)-stimulated glucose uptake was increased at 2 h after cessation of exercise in soleus muscle composed of predominantly slow-twitch fibers. This postexercise increase in insulin action of glucose uptake was accompanied by increased phosphorylation of AS160 (detected by phospho-Thr642 and phospho-Ser588 antibody). On the other hand, prior exercise did not increase phosphorylation of TBC1D1 (detected by phospho-Thr590) at 2 h postexercise. These results suggest the possibility that an enhancement in AS160 phosphorylation but not TBC1D1 phosphorylation is involved with increased postexercise insulin action of glucose uptake in slow-twitch muscle.

Keywords: AS160; TBC1D1; exercise; glucose uptake; insulin sensitivity; slow‐twitch muscle.

Figure 1.

(A) Insulin‐independent glucose uptake in rat soleus muscles immediately after treadmill exercise (180 min at 9 m/min). Details are provided in the Materials and Methods section. Muscles were dissected out immediately after exercise or a time‐matched resting period. Values are mean ± SE (n = 7–8). *P < 0.05 versus resting. (B) Basal and insulin‐stimulated glucose uptake in rat soleus muscles 120 min after treadmill exercise (180 min at 9 m/min). Muscles were dissected out 120 min after exercise or a time‐matched resting period. All muscles were incubated in glucose‐free medium in the absence or presence (50 or 10,000 μU/mL) of insulin for 20 min, followed by measurement of 2DG uptake. Values are means ± SE (n = 8). *P < 0.05 versus resting with same insulin concentration.

Figure 2.

Phosphorylation of Akt, AS160, and TBC1D1 in rat soleus muscles immediately after treadmill exercise (180 min at 9 m/min). Details are provided in the text. Frozen muscles were used to measure the phosphorylation of Akt Ser473 (A), Akt Thr308 (B), AS160 Thr642 (C), AS160 Ser588 (D), TBC1D1 Thr590 (E), and TBC1D1 Ser237 (F). Values are mean ± SE (n = 7–8). *P < 0.05 versus resting.

Figure 3.

Phosphorylation of Akt, AS160, and TBC1D1 in rat soleus muscles 2 h after treadmill exercise (180 min at 9 m/min). See the Materials and Methods section for details. Frozen muscles were used to measure the phosphorylation of Akt Ser473 (A), Akt Thr308 (B), AS160 Thr642 (C), AS160 Ser588 (D), TBC1D1 Thr590 (E), and TBC1D1 Ser237 (F). Values are mean ± SE, (A–D) n = 7–8; (E) n = 6–7; (F) n = 7–8. ^†P < 0.05 versus 0 μU/mL insulin. *P < 0.05 versus resting with same insulin concentration.