Tyramine and Vanadate Synergistically Stimulate Glucose Transport in Rat Adipocytes by Amine Oxidase-Dependent Generation of Hydrogen Peroxide

• Published in: The Journal of pharmacology and experimental therapeutics 1998-04, Vol.285 (1), p.342
• Main Authors: Marti, L, Morin, N, Enrique-Tarancon, G, Prevot, D, Lafontan, M, Testar, X, Zorzano, A, Carpéné, C
• Format: Article
• Language: English
• Subjects: Adipocytes - metabolism; Adrenergic alpha-Agonists - metabolism; Adrenergic alpha-Agonists - pharmacology; Amine Oxidase (Copper-Containing); Animals; Biological Transport; Drug Synergism; Glucose - metabolism; Glucose Transporter Type 4; Hydrogen Peroxide - metabolism; Male; Monosaccharide Transport Proteins - drug effects; Monosaccharide Transport Proteins - metabolism; Muscle Proteins; Oxidoreductases Acting on CH-NH Group Donors - metabolism; Rats; Rats, Wistar; Tyramine - metabolism; Tyramine - pharmacology; Vanadates - metabolism; Vanadates - pharmacology
• ISSN: 0022-3565; 1521-0103

Nonadrenergic imidazoline I 2 -binding sites colocalize with monoamine oxidase (MAO) in various tissues. As white adipocytes from various species have been reported to be very rich in I 2 -sites, the authors consider whether these cells show a substantial MAO activity and explore its functional role. Oxidation of [ 14 C]tyramine by rat adipocyte membranes was dependent on both MAO and semicarbazide-sensitive amine oxidase (SSAO). Tyramine oxidation was identical in membranes and in intact adipocytes ( V max : 11-12 nmol/min/mg protein). A similar effect of MAO and SSAO inhibitors was obtained in both the intact cells and the membranes: half of the activity was sensitive to semicarbazide and the other half more easily inhibited by MAO-A than by MAO-B inhibitors. As the reaction catalyzed by amine oxidases generates H 2 O 2 , which mimicks certain insulin effects in adipocytes, we tested whether tyramine oxidation influences glucose transport in adipocytes. One mM tyramine weakly stimulated glucose transport. A clear potentiation of tyramine effect occurred in the presence of 0.1 mM vanadate, ineffective by itself, reaching half-maximal insulin stimulation. This stimulation was sensitive to MAO and SSAO inhibitors and to catalase. The 5-fold activation of glucose transport was accompanied by translocation of GLUT4 transporters to the plasma membrane. This shows that tyramine is readily oxidized by adipocytes and potentiates the effects of vanadium on glucose transport through release of hydrogen peroxide. The role of the amine oxidases, which are highly expressed in adipocytes, allows them to be considered as more than mere scavengers of circulating amines.