Anticancer drug irinotecan inhibits homomeric 5-HT3A and heteromeric 5-HT3AB receptor responses

► Irinotecan, but not SN-38, inhibits 5-HT responses of 5-HT3A receptor. ► Irinotecan inhibition is competitive for 5-HT3A and 5-HT3AB receptor. ► Inhibitory effect on 5-HT3A receptor is more potent than that on 5-HT3AB receptor.