The Effect of 3,5,3′-Triiodo-L-Thyronine on the Kinetic Parameters of Sugar Transport in Cultured Chick Embryo Heart Cells

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Abstract
The effect of 3,5,3''-triiodo-L-thyronine (T3; 10-8M) on sugar transport was studied in cultured chick embryo heart cells. T3 did not increase the uptake of L-glucose, a sugar which enters the cell by simple diffusion. The effect of T3 on the kinetic parameters of the uptake of both 3-O-methyl-D-glucose (3-OMET) and 2-deoxy-D-glucose (2-DOG) was studied after 6 and 24 h exposure to T3. T3 had no effect on the Km, for either sugar. T3 increased the Vmax for the first 6 h of exposure for 3-OMET, a sugar which is only transported and increased the Vmax after 6 and 24 h for 2-DOG, a sugar both transported and phosphorylated. T3 also increased the relative phosphorylation of 2-DOG within the cells in the period between 6 and 24 h. The data showed a biphasic effect of T3 on sugar accumulation, an early effect on transport alone and a later effect on phosphorylation as well.