Agonist and antagonist effects of histamine H₃ receptor ligands on 5-HT₃ receptor-mediated ion currents in NG108-15 cells

The ability of histamine H₃ receptor ligands to interact with 5-HT₃ receptors in NG108-15 cells was studied using the whole cell patch clamp recording technique. Imetit, a histamine H₃ receptor agonist, generated inward currents and exhibited weak partial agonist activity at the 5-HT₃ receptor (EC₅₀=11.8 μM). Imetit-induced currents were slow to desensitize and at a high concentration reduced in size. The histamine H₃ receptor antagonists iodophenpropit and thioperamide did not generate inward currents but were able to inhibit 5-hydroxytryptamine (5-HT) responses with an IC₅₀ of 1.57±0.3 μM and 13.7±3.5 μM, respectively. Thioperamide is probably a non-competitive antagonist which may have more than one binding site on the receptor. Copyright (C) 1998 Elsevier Science B.V.