The shape of ramp-evoked AIS Na⁺ transients constrains the ratio of G_NaP densities in soma and AIS to a 0.3–3 range. Normalized AIS Na⁺ transients in experiment (left) and in models with different AIS-to-soma ratios of G_NaP density. In the model, the soma (length, 23 μm; diameter, 23 μm) gave rise to the 1.2-μm-thick axon. The Na⁺ transients were acquired from the middle of the 50-µm-long AIS. The horizontal dashed lines are to show the resting [Na⁺]_i level, and the vertical dashed lines are to show the time of ramp end. Somatic G_NaP density was kept constant at 5 pS/µm², and G_NaP density in the AIS was varied over the range of zero to threefold of the somatic density (numbers on the top of the figure). The model required the AIS G_NaP density to be one-third to threefold the somatic density to match the experimentally determined signals.