Figure 6. Model predicts I_NaP promotes excitability through AHP but not RMP.

(a,b) Model prediction of RMP (black), minimum voltage attained after an AP (AHP; blue) and SFR (red) at different levels of I_NaP for a WT-spiking (a) or WT-silent (b) SCN neuron at night. The WT-silent neuron does not spike with low to moderate levels of I_NAP, and has a SFR of zero and no AHP. When g_NaP is increased past a threshold level, the cell undergoes a ‘bifurcation' in its dynamics and begins to fire. When either neuron fires, increasing I_NaP increases the SFR without changing the RMP by decreasing the magnitude of the AHP. (c) Various currents (colour-coded in legend) associated with a typical SCN AP. During the AHP and ramp back to threshold, all currents other than I_NaP and I_KCa have inactivated. Scale bar, 40 ms. (d) Heat map showing the contributions of g_NaP and g_KCa towards setting the SFR (in Hz) of SCN neurons.