INSULIN AND GLUCOSAMINE INFUSIONS INCREASE O-LINKED N-ACETYL-GLUCOSAMINE IN SKELETAL-MUSCLE PROTEINS IN-VIVO

O-linked N-acetylglucosamine (O-GlcNAc) is an abundant posttranslation al modification of serine/threonine residues of nuclear and cytoplasmi c proteins. We determined whether insulin or coinfusion of glucosamine (GlcN) with insulin alters O-GlcNAc of skeletal muscle proteins. Thre e groups of conscious fasted rats received 6-hour infusions of either saline (BAS), insulin 18 mU/kg.min and saline (INS), or insulin and Gl cN 30 mu mol/kg.min (GLCN) during maintenance of normoglycemia. At 6 h ours, the concentrations of muscle UDP-GlcNAc, UDP-N-acetylgalactosami ne (UDP-GalNAc), UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), glyco gen, and N- and O-linked GlcNAc (galactosyltransferase labeling follow ed by beta elimination) were measured in freeze-clamped abdominis musc le. Insulin increased whole-body glucose uptake from 49 +/- 5 to 239 /- 8 mu mol/kg.min (P <.001) and glycogen in abdominis muscle from 138 +/- 11 to 370 +/- 26 mmol/kg dry weight (P <.001). Insulin increased the amount of cytosolic N- and O-linked GlcNAc by 56% from 362 +/- 30 to 564 +/- 45 dpm/mu g protein.100 min (P <.02), and O-GlcNAc from 221 +/- 16 to 339 +/- 27 dpm/mu g.100 min (P <.02). Glycogen content was positively correlated with the amount of total (r =.90, P <.005) and O -linked GlcNAc in insulin-infused animals. Coinfusion of GlcN with ins ulin increased muscle UDP-GlcNAc about fourfold (100 +/- 6 nmol/g) com pared with insulin (27 +/- 1, P <.001) or saline (25 +/- 1, P <.001) i nfusion, GlcN also decreased glucose uptake over 6 hours by 30% to 168 +/- 8 mu mol/kg.min (P <.001 for GLCN v INS) and muscle glycogen to 2 92 +/- 24 mmol/kg dry weight (P <.05 for GLCN v INS). Both total (635 +/- 60 dpm/mu g.100 min, P <.002) and O-linked GlcNAc (375 +/- 36 dpm/ mu g.100 min, P <.002) in the cytosol were significantly higher in GLC N rats (635 +/- 60 dpm/mu g) versus BAS rats (P <.002). As in INS rats , muscle glycogen and O-GlcNAc were positively correlated in GLCN rats (r =.54, P <.05). Variation in total and O-linked GlcNAc in GLCN rats was due both to GlcN (P <.02) and to variation in the glycogen conten t (P <.005). Copyright (C) 1998 by W.B. Saunders Company.