Induction of a high-affinity ketanserin binding site at the 5-hydroxytryptamine(1B) receptor by modification of its carboxy-terminal intracellular portion

Two chimeric 5-hydroxytryptamine (5-HT) receptors were constructed by excha nging the C-terminal portion of the human (h) 5-HT1B receptor with the equi valent domain of the h 5-HT2A receptor (5-HT1B/2A) Or With this domain trun cated from its last 44 amino acids (5-HT1B/2A Delta 44). The equilibrium di ssociation constant of the radioligand [H-3]GR 125743 was similar for both chimera compared to the wild-type (wt) h 5-HT1B receptor upon transient exp ression in COS-7 cells. Ketanserin binding affinity was 21-fold increased f rom pK(i): 5.79 (wt h 5-HT1B receptor) to pK(i): 7.11 at the 5-HT1B/2A chim eric receptor, this latter value being close to that of the wt h 5-HT1D rec eptor (pK(i): 7.62). This enhanced ketanserin binding affinity was lost whe n the last 44 C-terminal amino acids of the 5-HT,, receptor were deleted in the chimera 5-HT1B/2A Delta 44 (pK(i): 5.80). The binding affinities of th e 5-HT antagonists ritanserin, GR 125743, and SB-224289 were not modified a t either chimeric 5-HT receptor. The agonists F 11356, 5-HT, zolmitriptan, and sumatriptan yielded slightly increased (2- to 6-fold) binding affinitie s at both chimera as compared to the wt h 5-HT1B receptor. The present data suggest a role for the C-terminal intracellular receptor domain in modifyi ng ketanserin/5-HT1B receptor interactions. (C) 2000 Elsevier Science Inc.