[P3-0786] Acute heat stress activates glucose transport and 5’adenosine monophosphate-activated protein kinase in rat skeletal muscle
Keywords:skeletal muscle, heat stress, AMPK
【Purpose】The purpose of the present study was to investigate the short-term effect of heat stress on glucose transport and related signaling events in skeletal muscle during the period before an increase in heat shock protein（HSP）72.
【Methods】Male Sprague-Dawley rats weighting 150 g were killed by cervical dislocation without anesthesia, and epitrochlearis muscle was isolated. Muscle was then incubated in the absence or presence of heat stress（42℃, 10 or 30 min）in MEM a-based buffer containing 50 mU/ml insulin.
【Results】Heat stress for 30 min increased both hspa1a and hspa1b mRNA（p＜0.05）, but not HSP72 protein. Heat stress for 10 and 30 min robustly increased the rate of 3-O-methyl-glucose（3MG）transport（p＜0.05）, and the stimulatory effect of 3MG transport was blocked by cytochalasin B. Heat stress for 10 and 30 min decreased ATP, phosphocreatine, and glycogen concentrations（p＜0.05）. Correspondingly, heat stress for 10 min increased the phosphorylation level of 5’adenosine monophosphate-activated protein kinase（AMPK）α Thr172, and both AMPKα1 and AMPKα2 activities（p＜0.05）. Heat stress did not affect the phosphorylation status of Akt or CaMKII.
【Discussion】We demonstrated that heat stress acutely activates glucose transport prior to an increase in HSP72 protein in skeletal muscle. Blockade of glucose transport by cytochalasin B indicated that glucose is taken up into muscle cells via glucose transporter（GLUT）4. We also demonstrated that heat stress decreases the energy status and stimulates“cellular energy sensor”AMPK, a signaling intermediary leading to insulin-independent GLUT4 translocation. Considering that skeletal muscle is the major organ responsible for whole-body glucose metabolism and utilization, acute heat stress in skeletal muscle may be a useful modality for the improvement of glucose homeostasis in humans.
【Methods】Male Sprague-Dawley rats weighting 150 g were killed by cervical dislocation without anesthesia, and epitrochlearis muscle was isolated. Muscle was then incubated in the absence or presence of heat stress（42℃, 10 or 30 min）in MEM a-based buffer containing 50 mU/ml insulin.
【Results】Heat stress for 30 min increased both hspa1a and hspa1b mRNA（p＜0.05）, but not HSP72 protein. Heat stress for 10 and 30 min robustly increased the rate of 3-O-methyl-glucose（3MG）transport（p＜0.05）, and the stimulatory effect of 3MG transport was blocked by cytochalasin B. Heat stress for 10 and 30 min decreased ATP, phosphocreatine, and glycogen concentrations（p＜0.05）. Correspondingly, heat stress for 10 min increased the phosphorylation level of 5’adenosine monophosphate-activated protein kinase（AMPK）α Thr172, and both AMPKα1 and AMPKα2 activities（p＜0.05）. Heat stress did not affect the phosphorylation status of Akt or CaMKII.
【Discussion】We demonstrated that heat stress acutely activates glucose transport prior to an increase in HSP72 protein in skeletal muscle. Blockade of glucose transport by cytochalasin B indicated that glucose is taken up into muscle cells via glucose transporter（GLUT）4. We also demonstrated that heat stress decreases the energy status and stimulates“cellular energy sensor”AMPK, a signaling intermediary leading to insulin-independent GLUT4 translocation. Considering that skeletal muscle is the major organ responsible for whole-body glucose metabolism and utilization, acute heat stress in skeletal muscle may be a useful modality for the improvement of glucose homeostasis in humans.