Direct inhibition by cannabinoids of human 5-HT3A receptors: probable involvement of an allosteric modulatory site.
Excised outside-out patches from HEK293 cells stably transfected with the human (h) 5-HT3A receptor cDNA were used to determine the effects of cannabinoid receptor ligands on the 5-HT-induced current using the patch clamp technique. In addition, binding studies with radioligands for 5-HT3 as well as for cannabinoid CB1 and CB2 receptors were carried out. The 5-HT-induced current was inhibited by the following cannabinoid receptor agonists (at decreasing order of potency): 9-THC, WIN55,212-2, anandamide, JWH-015 and CP55940. The WIN55,212-2-induced inhibition was not altered by SR141716A, a CB1 receptor antagonist. WIN55,212-3, an enantiomer of WIN55,212-2, did not affect the 5-HT-induced current. WIN55,212-2 did not change the EC50 value of 5-HT in stimulating current, but reduced the maximum effect. The CB1 receptor ligand [3H]-SR141716A and the CB1/CB2 receptor ligand [3H]-CP55940 did not specifically bind to parental HEK293 cells. In competition experiments on membranes of HEK293 cells transfected with the h5-HT3A receptor cDNA, WIN55,212-2, CP55940, anandamide and SR141716A did not affect [3H]-GR65630 binding, but 5-HT caused a concentration dependent-inhibition. In conclusion, cannabinoids stereoselectively inhibit currents through recombinant h5-HT3A receptors independently of cannabinoid receptors. Probably the cannabinoids act allosterically at a modulatory site of the h5-HT3A receptor. Thus the functional state of the receptor can be controlled by the endogenous ligand anandamide. This site is a potential target for new analgesic and antiemetic drugs.
Barann
M
M
Institut für Pharmakologie und Toxikologie, Universität Bonn, Reuterstrasse 2b, D-53113 Bonn, Germany.
Molderings
G
G
Brüss
M
M
Bönisch
H
H
Urban
B W
BW
Göthert
M
M
D000495:Allosteric Site / Q000187:drug effects* / Q000502:physiology; D002186:Cannabinoids / Q000494:pharmacology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D011869:Radioligand Assay; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000819:agonists / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
D002186:Cannabinoids; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors