title: Control of muscle glucose uptake: test of the rate-limiting step paradigm in conscious, unrestrained mice.
abstract: The aim of this study was to test whether in fact glucose transport is rate-limiting in control of muscle glucose uptake (MGU) under physiological hyperinsulinaemic conditions in the conscious, unrestrained mouse. C57Bl/6J mice overexpressing GLUT4 (GLUT4(Tg)), hexokinase II (HK(Tg)), or both (GLUT4(Tg) + HK(Tg)), were compared to wild-type (WT) littermates. Catheters were implanted into a carotid artery and jugular vein for sampling and infusions at 4 month of age. After a 5-day recovery period, conscious mice underwent one of two protocols (n = 8-14/group) after a 5-h fast. Saline or insulin (4 mU kg(-1) min(-1)) was infused for 120 min. All mice received a bolus of 2-deoxy[(3)H]glucose (2-(3)HDG) at 95 min. Glucose was clamped at approximately 165 mg dl(-1) during insulin infusion and insulin levels reached approximately 80 microU ml(-1). The rate of disappearance of 2-(3)HDG from the blood provided an index of whole body glucose clearance. Gastrocnemius, superficial vastus lateralis and soleus muscles were excised at 120 min to determine 2-(3)HDG-6-phosphate levels and calculate an index of MGU (R(g)). Results show that whole body and tissue-specific indices of glucose utilization were: (1) augmented by GLUT4 overexpression, but not HKII overexpression, in the basal state; (2) enhanced by HKII overexpression in the presence of physiological hyperinsulinaemia; and (3) largely unaffected by GLUT4 overexpression during insulin clamps whether alone or combined with HKII overexpression. Therefore, while glucose transport is the primary barrier to MGU under basal conditions, glucose phosphorylation becomes a more important barrier during physiological hyperinsulinaemia in all muscles. The control of MGU is distributed rather than confined to a single rate-limiting step such as glucose transport as glucose transport and phosphorylation can both become barriers to skeletal muscle glucose influx.
authors.affiliation: Duke University Medical Center, Department of Pharmacology and Cancer Biology, 4321 Medical Park Drive, Suite 200, Durham, NC 27704, USA. patrick.fueger@duke.edu.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Fueger
authors.forename: Jane
authors.initials: J
authors.lastname: Shearer
authors.forename: Deanna P
authors.initials: DP
authors.lastname: Bracy
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Posey
authors.forename: R Richard
authors.initials: RR
authors.lastname: Pencek
authors.forename: Owen P
authors.initials: OP
authors.lastname: McGuinness
authors.forename: David H
authors.initials: DH
authors.lastname: Wasserman
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D000818:Animals; D001786:Blood Glucose / Q000032:analysis* / Q000378:metabolism; D003243:Consciousness / Q000187:drug effects / Q000502:physiology; D005260:Female; D005947:Glucose / Q000493:pharmacokinetics*; D051275:Glucose Transporter Type 4; D006593:Hexokinase / Q000378:metabolism*; D006801:Humans; D006946:Hyperinsulinism / Q000378:metabolism*; D007328:Insulin / Q000008:administration & dosage*; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; D006593:Hexokinase; D005947:Glucose