Figure 6. Phase–plane plot analysis of action potentials from repeated stimulations. A, Phase–plane plots of the first action potential in response to a repeated urine stimulation of 10 s duration with increasing IPIs ranging from 2 to 60 s, as indicated. Continuous and dashed lines were calculated from the first action potential of the first and second urine pulses, respectively. B–D, Scatter dot plots with the average ± SD of the ratio between the maximal dV/dt values of the first action potentials at each IPI. Urine pulse durations of 10 s (B), 5 s (C), and 2 s (D; for B: n = 6; Demsar’s test after Friedman test: p = 0.0021 for IPI 2 s; p = 0.0041 for IPI 5 s; for C: n = 6; Friedman test, p = 0.89; for D: n = 9; Friedman test, p = 0.051). E, Phase–plane plots of the first action potential in response to a repeated 5 pA current step of 10 s duration with increasing IPIs ranging from 2 to 60 s, as indicated. Continuous and dashed lines were calculated from the first action potential of the first and second current steps, respectively. F–H, Scatter dot plots with the average ± SD of the ratio between the maximal dV/dt values of the first action potentials at each IPI. Current step durations of 10 s (F), 5 s (G), and 2 s (H; for F: n = 8; Demsar’s test after Friedman test: p = 0.00054 for IPI 2 s; p = 0.018 for IPI 5 s; for H: n = 14; Friedman test, p = 0.126).