Simulated current–voltage relationship of 5-HT–induced (10 µM) peak current. Internal solutions containing (a) 0 M Na⁺/K⁺, (b) 0 M Na⁺/140 mM K⁺, and (c) 0 M K⁺/140 mM Na⁺ were used. The simulations reproduce experimental data described in Hasenhuetl et al. (2016).