Fig. 4. Simulation of membrane potential fluctuations with a computational model as described in Appendix 1. Three cases of Ca²⁺ sensitivity of ion channels are assumed. The parameter values used in the simulation are given in Appendix 1. (A) Membrane potential fluctuation and (B) a fluctuation histogram in Case I, in which neither K⁺ nor Ca²⁺ channels are assumed to have Ca²⁺ sensitivity. (C) Membrane potential fluctuation and (D) a fluctuation histogram in Case II, in which only K⁺ channels are assumed to have Ca²⁺ sensitivity. (E) Membrane potential fluctuation and (F) a fluctuation histogram in Case III, in which both K⁺ and Ca²⁺ channels are assumed to have Ca²⁺ sensitivity. Fluctuation amplitudes corresponding to the FWHMs of the distributions are shown on the right side of the histograms.