Iodothyronine Interactions with the System L1 Amino Acid Exchanger in 3T3-L1 Adipocytes

Figure 4

Concentration dependence of the inhibitory effect of tri-iodothyronine on phenylalanine uptake into 3T3-L1 adipocytes. Uptake of [³H]phenylalanine was measured at 5 $\mu$M over 3 minutes in the presence of 7 different T₃ concentrations as indicated (between 100 pM and 10 $\mu$M). Values are expressed as % of control phenylalanine uptake (measured in the absence of T₃). The dotted lines indicate that 50% inhibition is achieved with 1.2 $\mu$M T₃, estimated as the $K_i$ for T₃ inhibition of phenylalanine uptake in these cells.