EFFECTS OF NIDDM ON THE GLUCOSE-TRANSPORT SYSTEM IN HUMAN SKELETAL-MUSCLE

The purpose of this study was to investigate cellular changes in the glucose transport system in skeletal muscle of lean non-insulin-dependent diabetes mellitus (NIDDM) compared to lean nondiabetic control patients. NIDDM patients had significantly elevated fasting levels (means +/- SE) of serum glucose (10.1 +/- 1.3 vs. 5.4 +/- 0.4 mM, P < 0.001) and serum insulin (110.8 +/- 31.1 vs. 35.9 +/- 3.6 pM, P < 0.0025). Basal glucose transport (35.1 +/- 5.5 vs. 30.8 +/- 8.0 pM/mg protein) and cytochalasin-beta binding (3.5 +/- 1.2 vs 3.8 +/- 1.0 pM/mg protein) in isolated sarcolemmal vesicles were not significantly different between NIDDM and control groups. Insulin binding was reduced in NIDDM (0.82 +/- 0.03 vs. 1.63 +/- 0.18 pM/mg protein) as was the K(d) (0.93 +/- 0.03 vs. 1.38 +/- 0.12 nM). Tyrosine kinase activity, as assessed from incorporation of [P-32]ATP into Glu 4:Tyr 1, was significantly (P < 0.005) reduced in NIDDM at insulin concentrations from 1-100 nM. Maximum kinase activity was depressed (1.88 +/- 0.04 vs. 2.97 +/- 0.07 fM P-32/fM insulin binding at 100 nM insulin). The number of glucose transporters in the low-density microsomes was not significantly different between NIDDM and control groups (7.01 +/- 1.40 vs. 7.65 +/- 0.90 pM cytochalasin-beta bound/mg protein). These results suggest that decreased insulin binding and diminished receptor tyrosine kinase activity play a substantial role in the development of skeletal muscle insulin resistance associated with NIDDM.