Figure 2.

Mode changes of membrane excitability by varying P_CaV. (A) Bifurcation diagrams showing continuous changes in V_m of EPs or LCs as a function of P_CaV. Stable EPs, unstable EPs, stable LCs, and unstable LCs are indicated by black, red, blue, and yellow lines, respectively. The black line for a stable EP corresponds to the resting membrane potential, and the two blue lines for a stable LC correspond to the amplitude of the action potentials. The slow variables were fixed to the following values: [ATP] = 2.64 mM, [MgADP] = 0.0591 mM, [Re] = 0.61 mM, [Na⁺]_i = 5.87 mM, [K⁺]_i = 127 mM, [Ca²⁺]_i = 0.124 µM, [Ca²⁺]_ER = 0.0247 mM, f_us = 0.843, and I₁ = 0.152. Open circles indicate bifurcation points; LP, LP bifurcation; HB, Hopf bifurcation; PD, period doubling bifurcation. Black vertical lines with the blue italic numeral indicate control values of P_CaV (48.9 pA mM⁻¹) in the β-cell model. EP₁, EP₂, and EP₃ (gray dots) are the intersections of the EP curve with the black vertical line. Gray vertical lines passing through the corresponding bifurcation points separate individual modes, as indicated at the top. (B) Steady-state I-V relationship. Zero current potentials correspond to EP₁, EP₂, and EP₃ in A.