Identification and characterization of serotonin 5-HT4 receptor binding sites in human brain: comparison with other mammalian species.

Specific binding for the 5-HT4-selective radioligand [3H]GR 113808 has been identified in human and calf brain membranes. Using human tissue the distribution of the binding was heterogeneous throughout different brain regions, being highest in the caudate nucleus. For this region a Kd value of 0.59 +/- 0.08 nM and a Bmax of 225 +/- 2.6 fmol/mg were obtained. Other regions with substantial densities were the lenticular nucleus, the substantia nigra, the hippocampus and the frontal cortex, whereas no binding could be detected in the cerebellum. The ability of several standard compounds in displacing the radioligand was compatible with the labelling of 5-HT4 receptors. Correlation analysis showed no significant differences amongst data obtained for these compounds using human, calf and guinea-pig membranes.