Epinephrine translocates GLUT-4 but inhibits insulin-stimulated glucose transport in rat muscle.
We examined the effects of epinephrine (25, 50, and 150 nM) on 1) basal and insulin-stimulated 3-O-methylglucose (3-MG) transport in perfused rat muscles and 2) GLUT-4 in skeletal muscle plasma membranes. Insulin increased glucose transport 330-600% in three types of skeletal muscle [white (WG) and (RG) gastrocnemius and soleus (SOL)]. Glucose transport was also increased by epinephrine (22-48%) in these muscles (P < 0.05). In contrast, the insulin-stimulated 3-MG transport was reduced by epinephrine in all three types of muscles; maximal reductions were observed at 25 nM epinephrine in WG (-25%) and RG (-32.5%). A dose-dependent decrease occurred in SOL (-27% at 25 nM; -55% at 150 nM, P < 0.05). Insulin (20 mU/ml) and epinephrine (150 nM) each translocated GLUT-4 to the plasma membrane, and no differences in translocation were observed between insulin and epinephrine (P > 0.05). In addition, epinephrine did not inhibit insulin-stimulated GLUT-4 translocation, and the combined epinephrine and insulin effects on GLUT-4 translocation were not additive. The increase in surface GLUT-4 was associated with increases in muscle cAMP concentrations, but only when epinephrine alone was present. No relationship was evident between muscle cAMP concentrations and surface GLUT-4 in the combined epinephrine and insulin-stimulated muscles. These studies indicate that epinephrine can translocate GLUT-4 while at the same time increasing glucose transport when insulin is absent, or can inhibit glucose transport when insulin is present.
Han
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Department of Kinesiology, University of Waterloo, Ontario, Canada.
Bonen
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D019325:3-O-Methylglucose / Q000493:pharmacokinetics; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology*; D005947:Glucose / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051275:Glucose Transporter Type 4; D006614:Hindlimb; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D019325:3-O-Methylglucose; D000242:Cyclic AMP; D005947:Glucose; D004837:Epinephrine