piperidines and 7-azidoketanserin

Two azide analogues of ketanserin (6- and 7-azido-3-[2- [4-(4-fluorobenzoyl)-1-piperidinyl]ethyl]-2, 4(1H,3H)-quinazolinedione) were synthesized and tested as possible photoaffinity probes for serotonin-S2 and histamine-H1 receptors. In reversible binding experiments, the azides showed high affinity for both receptor types. When membrane preparations were incubated with nanomolar concentrations of 7-azidoketanserin and subsequently irradiated with UV light, both serotonin and histamine receptors became irreversibly blocked. This irreversible binding was dependent on azide concentrations and time of irradiation and did not change in the presence of the scavenger p-aminobenzoic acid. In contrast, irreversible blockade at low concentrations of 6-azidoketanserin was only obtained for histamine receptors. However, this blockade was abolished by addition of the scavenger p-aminobenzoic acid indicating that it was not due to a real photoaffinity mechanism. In the rat prefrontal cortex, irreversible blocking of serotonin receptors with 7-azidoketanserin could be inhibited by serotonin agonists or antagonists but not by histaminergic compounds. On the contrary, in the guinea pig cerebellum, inactivation of histamine receptors could be inhibited by histamine antagonists and histamine itself but not by serotonergic compounds. This provides a way for differential photolabeling of either of these receptors.

Topics: 4-Aminobenzoic Acid; Affinity Labels; Animals; Azides; Binding, Competitive; Cerebellum; Cerebral Cortex; Guinea Pigs; Histamine Antagonists; Ketanserin; Kinetics; Lysergic Acid Diethylamide; Photochemistry; Piperidines; Rats; Rats, Inbred Strains; Receptors, Histamine; Receptors, Histamine H2; Receptors, Serotonin; Serotonin Antagonists; Ultraviolet Rays

Topics: Affinity Labels; Animals; Azides; Female; Frontal Lobe; In Vitro Techniques; Ketanserin; Light; Piperidines; Rats; Rats, Inbred Strains; Receptors, Serotonin

7-Azidoketanserin, a potent photoaffinity probe for serotonin-S2 receptors was shown to irreversibly photoinactivate histamine-H1 receptors as well. The photolabelling of H1-receptors could be prevented by several selective histamine-H1 antagonists. In guinea pig cerebellum, a brain area that is highly enriched in H1-receptors, photolabelling could be directed exclusively to these receptors by adding a high concentration of pipamperone, which selectively blocks serotonin-S2 receptors. In rat pre-frontal cortex, a region that is enriched in serotonin-S2 receptors, pyrilamine was used to block H1-receptors, thereby directing the photolabelling exclusively to S2-receptors.

Topics: Affinity Labels; Animals; Azides; Binding, Competitive; Butyrophenones; Cerebellum; Cerebral Cortex; Female; Guinea Pigs; Ketanserin; Photolysis; Piperidines; Pyrilamine; Rats; Rats, Inbred Strains; Receptors, Histamine; Receptors, Histamine H1; Receptors, Serotonin; Spiperone