Heat stress acutely activates insulin-independent glucose transport and 5′-AMP-activated protein kinase prior to an increase in HSP72 protein in rat skeletal muscle

Abstract

Heat stress (HS) stimulates heat shock protein (HSP) 72 mRNA expression, and the period after an increase in HSP72 protein is characterized by enhanced glucose metabolism in skeletal muscle. We have hypothesized that, prior to an increase in the level of HSP72 protein, HS activates glucose metabolism by acutely stimulating 5′-AMP-activated protein kinase (AMPK). Rat epitrochlearis muscle was isolated and incubated either with or without HS (42°C) for 10 and 30 min. HS for 30 min led to an increase in the level of Hspa1a and Hspa1b mRNA but did not change the amount of HSP72 protein. However, HS for both 10 and 30 min led to a significant increase in the rate of 3-O-methyl-d-glucose (3MG) transport, and the stimulatory effect of 3MG transport was completely blocked by cytochalasin B. HS-stimulated 3MG transport was also inhibited by dorsomorphin but not by wortmannin. HS led to a decrease in the concentration of ATP, phosphocreatine, and glycogen, to an increase in the level of phosphorylation of AMPKα Thr172, and to an increase in the activity of both AMPKα1 and AMPKα2. HS did not affect the phosphorylation status of insulin receptor signaling or Ca2+/calmodulin-dependent protein kinase II. These results suggest that HS acts as a rapid stimulator of insulin-independent glucose transport, at least in part by stimulating AMPK via decreased energy status. Although further research is warranted, heat treatment of skeletal muscle might be a promising method to promote glucose metabolism acutely.

Heat stress induces mitochondrial adaptations in skeletal muscle

“…Importantly, there is no unified view on the effect of heat stress on AMPK. Previous studies on isolated muscles have been reported to activate AMPK by heat stress (42ºC, 10 min) 37) . In addition, opinions are divided on research targeting cultured cells (Activation 18) : 40ºC, 30 min; Inactivation 34) : 42ºC, 30 min).…”

The effect of short-term heat stress on protein synthesis signaling in isolated rat skeletal muscle

“…Muscles were exposed to HS as previously described 8) . Rats were fasted overnight prior to experimentation.…”

“…A separate set of muscle samples was subjected to western blot analysis, which was performed as previously described 8) , with modifications. Frozen muscle was homogenized in ice-cold buffer (1:40 wt/vol) [comprising 20 mmol/L Tris·HCl (pH 7.4), 1% Triton X-100, 50 mmol/L NaCl, 250 mmol/L sucrose, 50 mmol/L NaF, 5 mmol/L sodium pyrophosphate, 2 mmol/ L dithiothreitol, 4 mg/L leupeptin, 50 mg/L trypsin inhibitor, 0.1 mmol/L benzamidine, 1 mmol/L Na3VO4, and 0.5 mmol/L phenylmethylsulfonyl fluoride] and centrifuged at 16,000 g for 40 min at 4°C.…”

“…Short-term HS at 41°C for 20 min enhanced insulin-dependent glucose uptake in rat skeletal muscles 6) . Furthermore, HS at approximately 42°C for approximately 30 min stimulated insulin-independent glucose uptake, which was accompanied by energy depletion in rat skeletal muscles 7,8) . This HS-induced stimulation of glucose uptake was abrogated by an AMPK inhibitor 7,8) .…”

“…Furthermore, HS at approximately 42°C for approximately 30 min stimulated insulin-independent glucose uptake, which was accompanied by energy depletion in rat skeletal muscles 7,8) . This HS-induced stimulation of glucose uptake was abrogated by an AMPK inhibitor 7,8) . Therefore, these results suggested that HS enhances skeletal muscle glucose utilization via an AMPK-dependent mechanism.…”