Figure 1.
Atrial-ventricular differences in fast-Na+ current (INa) density–voltage relations. A: Representative current traces recorded from an atrial myocyte on depolarization to a range of voltages. Arrow indicates zero current level. Insert shows voltage pulse protocol. B: Representative current traces recorded from a ventricular myocyte on depolarization to a range of voltages. Arrow indicates zero current level. Voltage pulse protocol as for A. C: Mean INa density–voltage relations for atrial (filled circles, n = 17) and ventricular (open circles, n = 17) myocytes. Solid lines represent fits to Supplemental Equation 1. Data were significantly different by both cell type (P < .0001) and voltage (P < .0001), with significant interaction (P < .0001; 2-way repeated measures analysis of variance [RM ANOVA]). *P < .05; ****P < .0001 vs ventricular; Bonferroni post hoc test. Inset shows the corresponding mean INa density–voltage relations without normalization to whole-cell capacitance. Data were significantly different by both cell type (P = .0002) and voltage (P < .0001), with significant interaction (P < .0001; 2-way RM ANOVA). **P < .01; ****P < .0001 vs ventricular; Bonferroni post hoc test. D: Voltage dependence of time-to-peak INa (TTP) for atrial (filled circles, n = 17) and ventricular (open circles, n = 17) myocytes. Data were significantly different by both cell type (P < .0001) and voltage (P < .0001), with significant interaction (P = .0355; 2-way RM ANOVA). *P < .05; ****P < .0001 vs ventricular; Bonferroni post hoc test. The membrane time constants were 0.168 ± 0.009 ms for atrial myocytes (n = 17) and 0.327 ± 0.026 ms for ventricular cells (n = 17; P < .0001, unpaired Student t test).