Fig. 4.

The role of various ionic currents in the formation of afterdepolarization (ADP) following a parabolic burst as determined by the model, Eqs. (1)–(18). (a) Magnification of the last burst in Fig. 2a reveals an ADP after the last spike. (b) Model simulation of membrane potential during a parabolic burst. The ADP occurs in the interval [t₀, t₁], defined as the time between the nadir of the last spike (t₀) and some time after the ADP peak (t₁). (c) Contribution of Na⁺ currents I_Na = I_NaF + I_NaP (solid line), Ca²⁺ currents I_Ca = I_LVA + I_HVA + I_s (dashed line), and K⁺ currents I_K⁺ = I_K + I_A + I_KCa (dotted line) to afterdepolarization (I_ADP) within the interval [t₀, t₁], as defined by Eq. (20). Notice that while I_Na and I_Ca both contribute positively to the formation of ADPs, I_Ca diminishes progressively within the interval [t₀, t₁]. This causes the total inward current to decrease and the total outward current, led by I_KCa, to dominate and terminate the burst