Figure 3.

Chronic Depolarization Restored Tonotopic Differentiation of Kv1 Current

(A) [K⁺]_o in culture medium was elevated by 1.5 times (7.95 mM) for 1–14DIV by adding KCl to culture medium.

(B) Voltage responses to current injection after chronic depolarization. High- (left) and low-CF (right) neurons. Traces at −0.5 and 1 nA (thin) and that at threshold current (thick) are shown. Arrowheads indicate threshold potential.

(C) Voltage-current relationship measured at pulse end. Controls were from Figure 2B (gray).

(D) Threshold current of spikes. Controls were from Figure 2D (gray). Numbers in parentheses are the number of cells.

(E) Kv current after chronic depolarization. Tail current was expanded (inset). High- (left) and low-CF (right) neurons.

(F) Conductance-voltage curve of tail current. Magnified curve (inset). The curve was fitted to a double Boltzmann equation (red), and Kv1 and Kv3 components were shown in orange and green, respectively. Arrows indicate tail current at −40 mV, and roughly represents Kv1 current.

(G) Kv1 (left, orange) and Kv3 (right, green) currents calculated at +20 mV. Note that Kv1 current became larger by 4.5 times in high-CF neurons and 1.5 times in low-CF neurons after chronic depolarization.

(H) Immunostaining of Kv1.1 at 14DIV in control and after chronic depolarization (upper). High- (left) and low-CF (right) neurons. Intensity profile was plotted along a line (yellow) across the cells (lower).

(I and J) Signal intensity at cytoplasmic region (I) and relative intensity between membranous and cytoplasmic regions (J). Note that membranous signal was augmented in high-CF neurons after the depolarization.

**p < 0.01.