Biophysical characterization of I_h in neonatal (P1–4) WT and Hcn-deficient SGNs. (A) Family of representative I_h from WT, WT + 100 µM ZD7288, Hcn1^−/−, Hcn2^−/−, and Hcn1,2^−/− SGNs as indicated. Currents were evoked using the same voltage-clamp protocol shown in Fig. 2. Residual currents in Hcn1,2^−/− SGNs were blocked by 100 µM ZD7288. (B) Representative G_h activation curves for Hcn1^−/−, Hcn2^−/−, and Hcn1,2^−/− SGNs fitted with Boltzmann equations. V_1/2 and s are indicated on the graphs. (C) Summary of mean maximal G_h. (D) Summary of mean half-activation voltage. (E) Mean slope factor. Number of samples and genotype are indicated below. Error bars equal +1 SD. *, P < 0.05; **, P < 0.01; ***, P < 0.001.