title: A role for membrane transport in modulation of intramuscular free glutamine turnover in streptozotocin diabetic rats.
abstract: We wished to examine the effects of diabetes on muscle glutamine kinetics. Accordingly, female Wistar rats (200 g) were made diabetic by a single injection of streptozotocin (85 mg/kg) and studied 4 days later; control rats received saline. In diabetic rats, glutamine concentration of gastrocnemius muscle was 33% less than in control rats: 2.60 +/- 0.06 mumol/g vs. 3.84 +/- 0.13 mumol/g (P < 0.001). In gastrocnemius muscle, glutamine synthetase activity (Vmax) was unaltered by diabetes (approx. 235 nmol/min per g) but glutaminase Vmax increased from 146 +/- 29 to 401 +/- 94 nmol/min per g; substrate Km values of neither enzyme were affected by diabetes. Net glutamine efflux (A-V concentration difference x blood flow) from hindlimbs of diabetic rats in vivo was greater than control values (-30.0 +/- 3.2 vs. -1.9 +/- 2.6 nmol/min per g (P < 0.001)) and hindlimb NH3 uptake was concomitantly greater (about 27 nmol/min per g). The glutamine transport capacity (Vmax) of the Na-dependent System Nm in perfused hindlimb muscle was 29% lower in diabetic rats than in controls (820 +/- 50 vs. 1160 +/- 80 nmol/min per g (P < 0.01)), but transporter Km was the same in both groups (9.2 +/- 0.5 mM). The difference between inward and net glutamine fluxes indicated that glutamine efflux in perfused hindlimbs was stimulated in diabetes at physiological perfusate glutamine (0.5 mM); ammonia (1 mM in perfusate) had little effect on net glutamine flux in control and diabetic muscles. Intramuscular Na+ was 26% greater in diabetic (13.2 mumol/g) than control muscle, but muscle K+ (100 mumol/g) was similar. The accelerated rate of glutamine release from skeletal muscle and the lower muscle free glutamine concentration observed in diabetes may result from a combination of: (i), a diminished Na+ electrochemical gradient (i.e., the net driving force for glutamine accrual in muscle falls); (ii), a faster turnover of glutamine in muscle and (iii), an increased Vmax/Km for sarcolemmal glutamine efflux.
authors: Department of Anatomy and Physiology, University of Dundee, UK.
authors: H S
authors: HS
authors: Hundal
authors: P M
authors: PM
authors: Taylor
authors: N M
authors: NM
authors: Willhoft
authors: B
authors: B
authors: Mackenzie
authors: S Y
authors: SY
authors: Low
authors: M R
authors: MR
authors: Ward
authors: M J
authors: MJ
authors: Rennie
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000378:metabolism*; D005260:Female; D005973:Glutamine / Q000378:metabolism*; D008564:Membrane Potentials; D009132:Muscles / Q000378:metabolism*; D011188:Potassium / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000032:analysis
chemical_list: D000596:Amino Acids; D005973:Glutamine; D012964:Sodium; D011188:Potassium