ROLE OF SEMICARBAZIDE-SENSITIVE AMINE OXIDASE ON GLUCOSE-TRANSPORT AND GLUT4 RECRUITMENT TO THE CELL-SURFACE IN ADIPOSE-CELLS

The previous characterization of an abundant population of non-adrener gic imidazoline-I-2 binding sites in adipocytes and the recent demonst ration of the interplay between these binding sites and amine oxidases led us to analyze the amine oxidase activity in membranes from isolat ed rat adipocytes. Adipocyte membranes had substantial levels of semic arbazide-sensitive amine oxidase (SSAO), SSAO activity and immunoreact ive SSAO protein were maximal in plasma membranes, and they were also detectable in intracellular membranes, Vesicle immunoisolation analysi s indicated that GLUT4-containing vesicles from rat adipocytes contain substantial levels of SSAO activity and immunoreactive SSAO protein, Immunotitration of intracellular GLUT4 vesicles indicated that GLUT4 a nd SSAO colocalize in an endosomal compartment in rat adipocytes, SSAO activity was also found in GLUT4 vesicles from 3T3-L1 adipocytes and rat skeletal muscle. Benzylamine, a substrate of SSAO activity, caused a marked stimulation of glucose transport in isolated rat adipocytes in the presence of very low vanadate concentrations that by themselves were ineffective in exerting insulin-like effects. This synergistic e ffect of benzylamine and vanadate on glucose transport was totally abo lished in the presence of semicarbazide, a specific inhibitor of SSAO. Subcellular membrane fractionation revealed that the combination of b enzylamine and vanadate caused a recruitment of GLUT4 to the plasma me mbrane of adipose cells, The stimulatory effects of benzylamine and va nadate on glucose transport were blocked by catalase, suggesting that hydrogen peroxide production coupled to SSAO activity plays a crucial regulatory role, Based on these results we propose that SSAO activity might contribute through hydrogen peroxide production to the in vivo r egulation of GLUT4 trafficking in adipose cells.