Figure 8. Reducing Nav availability inverts net current covering the AHP from outward to inward.

A, top: AP-clamp experiment showing representative ctrl spike. (middle) K_v currents (red traces) were measured in a Tyrode standard solution with TTX (300 nm) and Cd²⁺ (200 μm). Ca²⁺ currents (black) were measured in the presence of TTX (300 nm) and high extracellular TEA (135 mm). Ca²⁺-activated K⁺ currents (blue) were obtained by subtracting from a control recording in Tyrode standard with TTX (300 nm) the K_V and the Ca²⁺ current. Bottom: close up. The grey rectangle indicates the AHP phase and the respective currents that sustain it. B and C, as for A, using a single spike stimulus protocol triggered from −40 mV and a spike doublet fired after complete block of Nav currents with 300 nm TTX. B, inset: net current amplitudes measured during the AHP phase indicated by the grey windows. C, inset: Ca²⁺ charge entering the cell during the AHP phase calculated by the integrating the corresponding Ca²⁺ inward current (*P < 0.05; ***P < 0.001; n = 9; ANOVA followed by a post hoc Bonferroni analysis).