Figure 5.

The B6-like, but not D2-like, isoform of TAAR1 is activated by MA in Taar1-transfected cells. HEK293 cells were stably transfected with GFP-tagged B6- or D2-like Taar1, and cAMP assays were performed as described in the text. (a) The B6-like isoform of TAAR1 responds to MA stimulation (EC₅₀=826 nM); however, the D2-like isoform does not, suggesting that the receptor is non-functional. Administration of the TAAR1 antagonist EPPTB (EC₅₀~60 μM) produced a right-ward shift in MA-induced cAMP accumulation in the B6-like recombinant TAAR1. Data shown are the average of at least three independent experiments, each conducted with duplicate determinations. Shown are means±SEM. There was a significant dose × receptor type interaction (F(18,56)=23.4; p<0.0001). *p<0.01 for the comparison between the indicated group and untransfected control. ⁺p<0.01 for the comparison between the MA alone and MA+EPPTB C57BL/6J TAAR1 groups. (b) Both the functional B6-like and the non-functional D2-like isoforms of TAAR1 were expressed in transfected cells. Untransfected (Untrans) cells did not express TAAR1. β-Actin was measured as a loading control. (c) Confocal images demonstrating expression of the functional B6-like and non-functional D2-like TAAR1 in cells. B6: C57BL/6J; D2: DBA/2J.