Figure 6. Apical dendrites express DTX-sensitive current.

A, in a representative outside-out patch pulled from the apical dendrite of a CA1 pyramidal cell, DTX (500 nm) reduced the outward K⁺ current. B, this plot shows the effect of DTX on individual dendritic outside-out patches. Each connected pair represents the potassium current amplitude obtained from the same patch in control condition and in the presence of DTX (500 nm). C, bar chart summarizing the effect of DTX on 12 patches from proximal apical dendrites (<100 μm from the soma). DTX caused a 16.4 ± 5.9% reduction of the total K⁺ current. **P < 0.01. D, DTX caused a rightward shift in the voltage dependence of activation of the dendritic potassium current. The data points, which represent population averages, were fitted with a Boltzmann equation. The resulting fit parameters were V_1/1/ = −15.9 mV, k = 13.7 in control, and V_1/ = 6.8 mV, k = 18.0 in DTX (n = 4 each, *P < 0.05).