The local translation of K_{Na} in dendritic projections of auditory neurons and the roles of K_{Na} in the transition from hidden to overt hearing loss

Figure 7.Reduced Na^{+} current density and available current in K_{Na}1 DKO SGNs. (A) Whole-cell inward Na^{+} currents were elicited using depolarizing steps from -70 mV to 35 mV (ΔV = 2.5 mV). The currents normalized to individual membrane capacitance (C_{m}), were recorded from 1-mo-old mice using basal SGNs from WT (shown with black traces) and DKO (shown with grey traces). Data were generated from 15 SGNs of each experimental group. (B) Consistent differences were noted in the peak Na^{+} current (I)- voltage (V) relation among WT (●) apical and DKO (●) SGNs. (C) In WT ~20% of the Na^{+} current is sustained, and in the DKO, ~10% persisted. Voltage-dependent activation and inactivation curves fitted with Boltzmann functions. Half-inactivation potentials (V_{1/2}) were measured by fitting plots to them. The V_{1/2} of the steady-state inactivation for WT was -69.5 ± 3.1 mV and the slope factor k, was, 5.1 ± 0.9 mV (n = 9) and DKO was -66.3 ± 2.7 mV and the slope factor k, was 7.3 ± 0.7 mV (n = 11). The activation curves for Na^{+} currents from WT and DKO were fitted with the Boltzmann function. The V_{1/2} for activation WT SGN was -45.1 ± 2.8 mV, and the slope factor k, was 3.1 ± 0.8 mV (n = 9) and DKO was -43.8 ± 2.6 mV, and the slope factor k, was 2.7 ± 0.5 mV (n = 11).