C, Strip immunoblots of ova-GLUT1, ova-GLUT4, and ova-GLUT12 incubated with the specific antibody directed against hGLUT1, hGLUT4, or hGLUT12 as indicated. In the presence of the immunization peptide, the bands labeled ova-GLUT12 and 58 kDa were absent, but the 52-kDa bands were not diminished, indicating that the 58-kDa band was specifically labeled by the anti-GLUT12 antibody. The GLUT12 blot contains strong nonspecific signals at about 52 kDa. The GLUT4 in the muscle samples exhibited a mobility suggesting 45 kDa, and the GLUT12 mobility suggested molecular size of 58 kDa. The lanes designated РІР‚СљaРІР‚Сњ and РІР‚СљbРІР‚Сњ contained 10 РћСg of muscle homogenate. Both of the ova-GLUT constructs shown here had mobility consistent with a molecular size of 40 kDa. A and B, Representative blots for GLUT4 and GLUT12 content in homogenates of muscle biopsies obtained from the vastus lateralis from normal volunteers. GLUT12 may have evolutionarily preceded GLUT4 and now provides redundancy to the dominant GLUT4 system in muscle.Р”Вirect comparison of muscle content of GLUT4 and GLUT12. Translocation of GLUT12 in cultured myoblasts was dependent on activation of PI3-K. Insulin causes GLUT12 to translocate from an intracellular location to the plasma membrane in normal human skeletal muscle. L6 myoblasts in culture also expressed and translocated GLUT12 in response to insulin, but inhibiting PI3-K prevented the translocation of GLUT12 and GLUT4. GLUT1 was predominantly in the PM fractions at baseline and did not change significantly after insulin. Insulin increased GLUT4 in PM from 13 to 42%. In human muscle, insulin caused a shift of a portion of GLUT12 from intracellular low-density microsomes to the plasma membrane (PM) fraction (17% in PM at baseline, 38% in PM after insulin). Insulin was infused at 40 mU/m(2) x min for 3 h. Cultured myoblasts were used to determine whether GLUT12 translocation was phosphatidyl inositol-3 kinase (PI3-K)-dependent. GLUT12, GLUT4, and GLUT1 proteins were quantified in muscle biopsy fractions. Subjects were nonobese, young adults with no family history of diabetes. Infusions and biopsies were performed in an outpatient clinic. Six normal volunteers had muscle biopsies before and after euglycemic insulin infusions.

This study was intended to determine whether insulin caused GLUT12 translocation in muscle. In GLUT4 null mice, insulin-stimulated glucose uptake into muscle was diminished but not eliminated, suggesting that another insulin-sensitive system was present. GLUT4 is the predominant glucose transporter isoform expressed in fat and muscle.

Parallels transporter