Hexose transporter mRNAs for GLUT4, GLUT5, and GLUT12 predominate in human muscle

Departments of 1 Internal Medicine and 2 Microbiology, East Tennessee State University James H. Quillen College of Medicine, Johnson City, Tennessee; and 3 Department of Surgery, The University of Texas Medical Branch at Galveston, Galveston, Texas Submitted 24 May 2006 ; accepted in final form 20 June 2006 In the past few years, 8 additional members of the facilitative hexose transporter family have been identified, giving a total of 14 members of the SLC2A family of membrane-bound hexose transporters. To determine which of the new hexose transporters were expressed in muscle, mRNA concentrations of 11 glucose transporters (GLUTs) were quantified and compared. RNA from muscle from 10 normal volunteers was subjected to RT-PCR. Primers were designed that amplified 78- to 241-base fragments, and cDNA standards were cloned for GLUT1 , GLUT2 , GLUT3 , GLUT4 , GLUT5 , GLUT6 , GLUT8 , GLUT9 , GLUT10 , GLUT11 , GLUT12 , and GAPDH . Seven of these eleven hexose transporters were detectable in normal human muscle. The rank order was GLUT4 , GLUT5 , GLUT12 , GLUT8 , GLUT11 , GLUT3 , and GLUT1 , with corresponding concentrations of 404 ± 49, 131 ± 14, 33 ± 4, 5.5 ± 0.5, 4.1 ± 0.4, 1.2 ± .0.1, and 0.9 ± 0.2 copies/ng RNA (means ± SE), respectively, for the 10 subjects. Concentrations of mRNA for GLUT4 , GLUT5 , and GLUT12 were much higher than those for the remainder of the GLUTs and together accounted for 98% of the total GLUT isoform mRNA. Immunoblots of muscle homogenates verified that the respective proteins for GLUT4, GLUT5, and GLUT12 were present in normal human muscle. Immunofluorescent studies demonstrated that GLUT4 and GLUT12 were predominantly expressed in type I oxidative fibers; however, GLUT5 was expressed predominantly in type II (white) fibers. glucose transporter 1; glucose transporter 3 Address for reprint requests and other correspondence: C. A. Stuart, East Tennessee State Univ., James H. Quillen College of Medicine, PO Box 70622, Johnson City, TN 37614-0622 (e-mail: stuartc{at}mail.etsu.edu )