Quetiapine competitively inhibits 5-HT₃ receptor-mediated currents in NCB20 neuroblastoma cells

The 5-hydroxytryptamine type₃ (5-HT₃) receptor, a ligand-gated ion channel, plays a critical role in synaptic transmission. It has been implicated in various neuropsychiatric disorders. This study aimed to elucidate the mechanism by which quetiapine, an atypical antipsychotic, could inhibit 5-HT₃ receptor-mediated currents in NCB20 neuroblastoma cells. Whole-cell patch-clamp recordings were used to study effects of quetiapine on receptor ion channel kinetics and its competitive antagonism. Co-application of quetiapine shifted 5-HT concentration-response curve rightward, significantly increasing the EC50 without altering the maximal response (E_max), suggesting a competitive inhibition. Quetiapine's IC₅₀ varied with 5-HT concentration and treatment condition. The IC₅₀ value of quetiapine was 0.58 μM with 3 μM 5-HT and 25.23 μM with 10 μM 5-HT, indicating an inverse relationship between quetiapine efficacy and agonist concentration. Pretreatment of quetiapine significantly enhanced its inhibitory potency, reducing its IC₅₀ from 25.23 μM to 0.20 μM. Interaction kinetics experiments revealed an IC₅₀ of 5.17 μM for an open state of the 5-HT₃ receptor, suggesting weaker affinity during receptor activation. Quetiapine also accelerated receptor deactivation and desensitization, suggesting that it could stabilize the receptor in non-conducting states. Additionally, quetiapine significantly prolonged recovery from desensitization without affecting recovery from deactivation, demonstrating its selective impact on receptor kinetics. Inhibition of the 5-HT₃ receptor by quetiapine was voltage-independent, and quetiapine exhibited no use-dependency, further supporting its role as a competitive antagonist. These findings provide insights into inhibitory mechanism of quetiapine on 5-HT₃ receptor and suggest its potential therapeutic implications for modulating serotonergic pathways in neuropsychiatric disorders.