Fig 4. Modeling conductance heterogeneity using virtual populations of isolated SAN cells.

(A) The effect of heterogeneous ionic channel expression on the automaticity of SAN cells was compared across models. In all three models the percentage of dormant cells rose with increasing levels of heterogeneity. (B) The effect of heterogeneity on the SA node AP properties was evaluated in spontaneously beating cells, by measuring cycle length (CL), AP amplitude (APA) and AP duration (APD) at varying σ levels. Outliers (values more than three median absolute deviations) were removed from distributions. (C) Logistic regression analysis was utilized to deduce which specific ionic currents across the three models are responsible for SA node cell’s automaticity. Positive values indicate that an increase in the parameter increases the probability of the cell to be spontaneously beating.