Fig 1: Supraclinical concentrations of psilocin inhibit hERG channels heterologously expressed in tsA-201 cells. (A) Chemical structures of psilocybin (black) and its metabolites psilocin (blue) and 4-hydroxyindole-3-acetic acid (4-HIAA, red). (B) Potassium currents through hERG channels in tsA-201 cells recorded with the whole-cell patch clamp technique as previously described (Koenig et al., 2013). Voltage-clamp pulse protocol (top; pulses applied every 15 seconds) with representative original current traces. (C) Current-voltage relationship of the experiment displayed in B; throughout the figure, filled or open circles represent evaluation of current amplitude at the end of the 4-second prepulse (+10 mV) or at the peak of tail current (−50 mV), respectively. (D) Voltage-clamp protocol (applied every 15 seconds) to test for the effect of drugs on hERG channels and respective representative potassium currents before (control) and after equilibration with different concentrations of psilocin (Serobac, PSI-410-FB-10; 100 mM stock dissolved in DMSO, final concentrations: 0.1–100 µM), 4-HIAA (PubChem 7061393; AKos Consulting & Solutions AKOS003270455; 100 mM stock in DMSO, final concentration: 100 µM), and E4031 (selective hERG channel inhibitor; Sigma Aldrich M5060; 1 mM stock in H2O, final concentration: 1 µM). (E) Concentration response curve for hERG current inhibition by psilocin (blue); fit of the data to a Hill equation yielded an IC50 value of 55 ± 10 µM (42 ± 6 µM) with a Hill coefficient of 0.8 ± 0.1 (0.8 ± 0.1) at −50 mV (+10 mV). n = 5 independent experiments; data are expressed as means ± SD. In addition, relative hERG current level on application of 100 µM 4-HIAA (n = 6, red) or 1 µM E4031 (n = 5, green) is displayed.