Binding thermodynamics of serotonin to rat-brain 5-HT1A, 5HT2A and 5-HT3 receptors.

The thermodynamic parameters delta G degrees, delta H degrees and delta S degrees of the binding equilibrium of serotonin to 5-HT1A, 5-HT2A and 5-HT3 rat-brain membrane receptors have been determined by means of affinity constant measurements at six temperatures in the range 0 -35 degrees C and van't Hoff plots. At variance with 5-HT1A and 5-HT3, the binding at the 5-HT2A receptors is strongly endothermic and entropy-driven. Comparison with the results obtained by other authors on 5-HT2A receptors in rats and humans suggests that the observed differences can be explained by a single amino acid difference in the receptor sequence between these two species.