Hexokinase kinetics in human skeletal muscle after hyperinsulinaemia, hyperglycaemia and hyperepinephrinaemia.
The effects of 120 min of euglycaemic hyperinsulinaemia (UH, approximately 5 mM; 40 mU m-2 min-1), UH plus adrenaline infusion (0.05 microgram kg-1 min-1), and hyperglycaemic normoinsulinaemia (26 mM) on hexokinase kinetics in human skeletal muscle were examined. Biopsies were obtained from the quadriceps femoris muscle before and after each clamp. Total muscle hexokinase activity (HKt) (measured on a 2500 g supernatant) at a saturating level of the substrate glucose (1 mM) averaged 13 mmol kg dry wt-1 min-1 in the basal state and did not change significantly under any condition. Soluble hexokinase activity (HKs) (16,000 g supernatant) accounted for approximately 65% of HKt in the basal state, and this percentage was not significantly affected by any condition, suggesting that there was no major transfer of HK between cytosol and mitochondria. The activity of HKt and HKs was inhibited by glucose 1,6-bisphosphate (G-1,6-P2) in a concentration dependent manner in the basal state, and the sensitivity to G1,6-P2 inhibition was not altered by any condition. The activity of HKt and HKs in the presence of a subsaturating level of glucose (0.1 mM) accounted for approximately 70% of the activity at 1 mM glucose, and this percentage was not altered by any condition. These data suggest that under the present conditions alterations in the rates of whole body glucose disposal cannot be associated with alterations in HK distribution between cellular compartments nor its measured kinetics properties.
Katz
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A
Department of Clinical Physiology, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden.
Raz
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I
D004837:Epinephrine / Q000097:blood*; D005947:Glucose / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives*; D005958:Glucosephosphates / Q000494:pharmacology; D006593:Hexokinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism*; D006946:Hyperinsulinism / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*
D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; C016473:glucose-1,6-bisphosphate; D006593:Hexokinase; D005947:Glucose; D004837:Epinephrine