QUANTITY OF NA K-ATPASE AND GLUCOSE TRANSPORTERS IN THE PLASMA-MEMBRANE OF RAT ADIPOCYTES IS REDUCED BY IN-VIVO TRIIODOTHYRONINE/

The expression of sodium-potassium pumps and glucose transporters in p ure adipocyte plasma membranes from a hyperthyroid animal model was st udied. Hyperthyroidism was induced by enteral administration of five d oses of 90 mu g of triiodothyronine every second day to 8-week-old rat s. Following isolation of epididymal adipocytes, 3-O-methylglucose tra nsport was measured and the number of Na/K-ATPase-(alpha(1)- and alpha (2)-isoforms) and glucose transporter (GLUT1 and GLUT4) molecules in s heets of adipocyte plasma membrane were determined by quantitative imm unoelectron microscopy, using gold labelling. Maximal in vitro insulin stimulation of adipocytes increased the glucose transport rate and th e amount of GLUT4 in the plasma membrane 15-fold, whereas the amount o f alpha(2) was unaffected. In adipocytes from hyperthyroid rats, mean adipocyte volume was decreased by 18% and the quantities of GLUT4 per unit area of plasma membrane (maximal insulin stimulation) and of alph a(2) were decreased by 19% and 15%, respectively. Thus, hypotrophia of fat tissue in the hyperthyroid state is associated with a decreased e xpression in the plasma membrane of the glucose transporter GLUT4 and the alpha(2)-isoform of Na/K-ATPase.