Figure 3

Fragments of SB269652 contaiing the THIQ core display competitve pharmacology and lower affinity in the absence of an Na⁺ ion coordinated by D80^2.50. (A) In the presence of 100 mM NaCl (closed symbols) the fragment of SB269652, 2-propyl-1,2,3,4-tetrahydroisoquinoline-7-carbonitrile (2, MIPS1071) acts to completely displace [³H]spiperone in a competition binding assay using membranes from FlpIN CHO cells stably expressing the WT hD_2LR. The affinity of MIPS1071 is unchanged at the E95^2.65A receptor mutant but decreased at the D80^2.50A receptor mutant. In the absence of 100 mM NaCl (100 mM NMDG, open symbols), the affinity of MIPS1071 is decreased at the WT D_2LR and E95^2.65A mutant but unchanged at the D80^2.50A mutant. (B) In the presence of 100 mM NaCl (closed symbols) N-((trans)-4-(2-(7-cyano-3,4- dihydroisoquinolin-2(1 H)yl)ethyl)cyclohexyl)acetamide (3, MIPS1059), a fragment that includes the carboxamide but not the indole moiety of SB269652, acts to completely displace [³H]spiperone in a competition binding assay using membranes from FlpIN CHO cells stably expressing the WT hD_2LR. The affinity of MIPS1059 is decreased at both the E95^2.65A and D80^2.50A receptor mutants. In the absence of 100 mM NaCl (100 mM NMDG, open symbols), the affinity of MIPS1071 is significantly decreased at the WT D_2LR and E95^2.65A mutant but unchanged at the D80^2.50A mutant.