Regulation of insulin-stimulated muscle glucose uptake in the conscious mouse: role of glucose transport is dependent on glucose phosphorylation capacity.
Previous work suggests that normal GLUT4 content is sufficient for increases in muscle glucose uptake (MGU) during hyperinsulinemia, because glucose phosphorylation is the more formidable barrier to insulin-stimulated MGU. It was hypothesized that a partial ablation of GLUT4 would not impair insulin-stimulated MGU when glucose phosphorylation capacity is normal but would do so when glucose phosphorylation capacity is increased. Thus, chow-fed C57BL/6J mice with a GLUT4 partial knockout (GLUT4(+/-)), hexokinase II overexpression (HK(Tg)), or both (HK(Tg) + GLUT4(+/-)) and wild-type littermates were studied. Carotid artery and jugular vein catheters were implanted for sampling and infusions at 4 months of age. After a 5-d recovery, 5-h fasted mice (n = 8-11/group) underwent a 120-min saline infusion or insulin clamp (4 mU/kg.min insulin with glucose maintained at 165 mg/dl) and received a 2-deoxy[(3)H]glucose bolus to provide an index of MGU (R(g)) for the soleus, gastrocnemius, and superficial vastus lateralis. Basal R(g) from all muscles studied from saline-infused mice were not changed by any of the genetic modifications. HK(Tg) mice had augmented insulin-stimulated R(g) in all muscles studied compared with remaining genotypes. Insulin-stimulated R(g) was not impaired in any of the muscles studied from GLUT4(+/-) mice. However, the enhanced insulin-stimulated R(g) created by HK overexpression was ablated in HK(Tg) + GLUT4(+/-) mice. Thus, a 50% reduction of normal GLUT4 content in the presence of normal HK activity does not impair insulin-stimulated MGU. However, when the glucose phosphorylation barrier is lowered by HK overexpression, GLUT4 availability becomes a limitation to insulin-stimulated MGU.
Fueger
Patrick T
PT
Duke University Medical Center, Department of Pharmacology and Cancer Biology, 4321 Medical Park Drive, Suite 200, Durham, North Carolina 27704, USA. patrick.fueger@duke.edu
Hess
Holli S
HS
Bracy
Deanna P
DP
Pencek
R Richard
RR
Posey
Kelly A
KA
Charron
Maureen J
MJ
Wasserman
David H
DH
D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism*; D003243:Consciousness; D005260:Female; D051275:Glucose Transporter Type 4; D006593:Hexokinase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism*; D010766:Phosphorylation
D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; D006593:Hexokinase