Histamine effects on the 5-HT1c receptor expressed in Xenopus oocytes

To analyze the cross-reactivity between serotonin (5-HT) and histamine, the in vitro transcribed RNA for the 5-HT1c receptor was functionally expressed in Xenopus oocytes. 5-HT significantly increased 45Ca2+ efflux in RNA-injected oocytes, but not in uninjected and water-injected control oocytes. Furthermore, histamine and the H1 receptor agonists, but not the H2 and H3 agonists, significantly induced 45Ca2+ efflux in 5-HT1c receptor RNA-injected oocytes, but not in uninjected and water-injected oocytes. However, the H1, H2, and H3 antagonists failed to inhibit histamine-induced 45Ca2+ efflux at 10(-6) M. This finding suggests that the 5-HT1c receptor can be activated by both 5-HT and histamine, although the action of histamine is different from classic histamine pharmacology.