Species variations in 5-HT3 recognition sites labeled by 3H-quipazine in the central nervous system

The specific binding of 3H-quipazine to putative 5-HT3 receptors was analyzed in multiple species. Specific and saturable binding of the radioligand could be detected in both rat (KD = 1.2 nM; Bmax = 3.0 pmol/g) and pig (KD = 1.3 +/- 0.2 nM; Bmax = 1.5 +/- 0.2 p/mol/g) cortical membranes. By contrast, no significant specific binding of 3H-quipazine could be detected in human, cow, dog, turtle, mouse, guinea pig, chicken or rabbit brain membranes. These data indicate that marked species variations exist in the presence and/or density of 5-HT3 membrane recognition sites in the central nervous system.