Nucleotide interactions with 5-HT1A binding sites directly labeled by [3H]-8-hydroxy-2-(DI-n-propylamino)tetralin...

Nucleotide interactions were examined at 5-hydroxytryptamine1A (5-HT1A) binding sites labeled by [3H]-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). At a 10(-4) M concentration, GTP and GDP decreased specific binding of 0.4 nM [3H]-8-OH-DPAT to 47 +/- 4 and 61 +/- 1% of control values respectively. This nucleotide effect was significantly greater (P less than 0.005) than observed at total 5-HT1 binding sites labeled by 1.5 nM [3H]-5-HT. GMP and adenine nucleotides had a minimal effect on [3H]-8-OH-DPAT binding at concentrations less than 10(-3) M. Saturation experiments demonstrated that 10(-4) M GTP increased the KD of [3H]-8-OH-DPAT for 5-HT1A binding sites (0.79 to 2.7 nM) without changing the number of binding sites (1.98 to 1.93 pmoles/g tissue). The Ki values of classic and novel putative 5-HT agonists were increased 2- to 4-fold in the presence of 10(-4) M GTP. Affinities of 5-HT antagonists for the [3H]-8-OH-DPAT site were not affected by the addition of 10(-4) M GTP to the binding assay.