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. 2016 Jan 6;36(1):222–234. doi: 10.1523/JNEUROSCI.1808-15.2016

Figure 5.

Figure 5.

Np65 is not required for the normal development of the MET apparatus. A, Scanning electron micrographs of the apical and basal coil of the cochlea from P16 Nptn+/+ (left) and Nptnpitch/pitch (right) showing that the stereocilia bundle structure of IHCs and OHCs appears similar between the two genotypes. B, Number of apical and basal IHCs per 10 pillar cells from Nptn+/+ (white bar) and Nptnpitch/pitch (black bar) mice at P16 and P27. We found no significant IHC loss in the mutant mice compared with wild-type controls at both ages tested. C, Apical and basal OHC counts per 10 pillar cells from Nptn+/+ and Nptnpitch/pitch mice at P16 and P27. A significant loss of OHCs was only observed in the basal turn of the cochlea from Nptnpitch/pitch mice at both ages: *p < 0.05; **p < 0.01. D, E, Saturating MET currents recorded from a P6 control (D) and pitch mutant (E) apical-coil OHC by applying voltage steps from −121 mV to 99 mV in 20 mV increments (holding potential −81 mV). For clarity, only two voltage steps are shown. During the voltage steps, hair bundles were displaced by applying a 50 Hz sinusoidal force stimuli (the driver voltage [DV] to the fluid jet is shown above the traces). Negative deflections of the DV are inhibitory. Arrows indicate the closure of the transducer channels (i.e., disappearance of the resting current) during inhibitory bundle displacements. Dashed lines indicate the holding current, which is the current at the holding potential of −81 mV. F, Peak-to-peak current–voltage curves obtained from 10 controls and eight pitch mutant OHCs (P6). The fits through the data are according to a single-energy-barrier model (Géléoc et al., 1997): I(V) = k [exp ((1 − γ) (V − Vr)/Vs) −exp (−γ(V − Vr)/Vs)], where k is a proportionality constant, Vr is the reversal potential, Vs is a measure for the steepness of the rectification, and γ is the fractional distance within the membrane's electrical field of an energy barrier, as measured from the outside. The values are as follows: control k = 445 ± 37, Vr = 0.4 ± 0.1 mV, Vs = 39 ± 3 mV, γ = 0.42 ± 0.01; pitch mutant k = 428 ± 31, Vr = 0.1 ± 0.2 mV, Vs = 38 ± 2 mV, γ = 0.42 ± 0.01.