The voltage sag and afterdepolarization (ADP) values were plotted against the level of the injected current and the corresponding relationships were fitted with linear functions. The slope of the linear fits is proportional with the magnitude of the voltage sag and ADP associated with the action of intrinsic h-current. The data are presented as mean ± SEM. Statistical significance * p < 0.05 was calculated by one-way ANOVA followed with Tukey’s test. For post-hoc group comparisons: * = significant difference for IL-6 tg −/− vs IL-6 tg +/+ (p < 0.01); # = significant difference for IL-6 tg +/− vs IL-6 tg +/+ mice (p < 0.01).