Comparison of GLUT1, GLUT3, and GLUT4 mRNA and the subcellular distribution of their proteins in normal human muscle

Basal, "insulin-independent" glucose uptake into skeletal muscle is provide d by glucose transporters positioned at the plasma membrane. The relative a mount of the three glucose transporters expressed in muscle has not been pr eviously quantified. Using a combination of qualitative and quantitative ri bonuclease protection assay (RPA) methods, we found in normal human muscle that GLUT1, GLUT3, and GLUT4 mRNA were expressed at 90 +/- 10, 46 +/- 4, an d 156 +/- 12 copies/ng RNA, respectively. Muscle was fractionated by DNase digestion and differential sedimentation into membrane fractions enriched i n plasma membranes (PM) or low-density microsomes (LDM). GLUT1: and GLUT4 p roteins were distributed 57% to 67% in LDM, whereas GLUT3 protein was at le ast 88% in the PM-enriched fractions. These data suggest that basal glucose uptake into resting human muscle could be provided in part by each of thes e three isoforms. Copyright (C) 2000 by W.B. Saunders Company.