Direct inhibition by cannabinoids of human 5‐HT3A receptors: probable involvement of an allosteric modulatory site
Tóm tắt
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): Δ9‐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.
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Tài liệu tham khảo
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