Spike waveforms in the HH model with varied BK.

(A) shows the voltage, IBK current, and IBK activation behaviour of a spike induced by a 5-nA current step for 5 ms, in the original oxytocin HH model (yellow, τpd = 1.22 ms), and the adjusted model (green; τpd = 10 ms). Experimentally, the HAP lasts for 25–125 ms and hyperpolarises the cell by ~7.5 mV [18]. In the original HH model, the HAP is too short and too small, because IBK both rises and falls sharply after a spike. In the adjusted model, IBK is prolonged by the slower deactivation, making a better match to the HAP observed in vitro, as well as improving the fit to the in vivo ISI distribution. (B) shows, for the adjusted model, the effects of setting gBK = 0 (red, compared to original value gBK = 1, in green), on a single spike induced by an 8-nA current step for 3 ms, to simulate the pharmacological block of IBK [18]. When IBK is blocked, the HAP is smaller and decays faster. (C) shows the in vitro experiment data simulated in (B), redrawn from [18]. The duration and amplitude of the HAP is a much closer match to the adjusted model. The block shows only a partial reduction, but is likely to be less total than the model.