Cloned human and murine serotonin_3A receptors expressed in human embryonic kidney 293 cells display different single-channel kinetics

In the present study, well-resolved single-channel events of cloned human and murine homomeric 5-hydroxytryptamine type 3 (h5-HT_3A and m5-HT_3A) receptors, expressed in human embryonic kidney 293 cells, are reported for the first time. 5-HT (1 μM) applied in Ca²⁺- and Mg²⁺-free external solution to excised outside-out membrane patches induced non-rectifying single-channel inward currents. These currents were not observed in untransfected cells or in the presence of the antagonist ondansetron (1 μM). The mean single-channel conductance of the h5-HT_3A and m5-HT_3A receptors was 48±8 pS and 46±7 pS, the mean reversal potential was 10.3±1.8 mV and 4.7±5.3 mV, respectively. The analysis of single-channel open-times revealed for both h5-HT_3A and m5-HT_3A receptors only one type of open state, but different mean open-times (7.1±2.9 ms vs. 4.1±0.8 ms) indicating species-dependent gating mechanisms of 5-HT₃ receptors.