Figure 5

The P1308L and V1298F mutations enhance the response to slow ramp depolarization. HEK293 cells were held at -100 mV and a depolarizing voltage ramp from -100 mV to +20 mV was applied at a rate of 0.2 mV/ms. A, Representative ramp currents from WT (black), P1308L (red), and V1208F (grey) channels. Currents were normalized to maximal peak currents elicited by step depolarizations in Figure 1B. B, Both P1308L and V1298F mutations significantly increase the relative amplitude of ramp currents (WT: 0.26 ± 0.03%, n = 12; P1308L: 1.09 ± 0.11%, n = 15, p < 0.001 vs WT; V1298F: 0.58 ± 0.06%, n = 16, p = 0.015 vs WT). C, The potential of peak ramp currents was more negative in P1308L mutant channels than in WT and V1298F channels (WT: -44.8 ± 1.4 mV, n = 12; P1308L: -51.1 ± 0.9 mV, n = 15, p < 0.001 vs WT; V1298F: -42.5 ± 0.8 mV, n = 16, p = 0.280 vs WT).