Figure 3.

Characteristics of Ca²⁺ currents in 3-month-old SGNs from apical and basal turns of the cochlea, and the effects of Ca²⁺ current blockers. A, Family of inward Ca²⁺ currents from apical SGN elicited from a holding potential of −70 mV to step potentials from −50 to 30 mV in 10 mV increments (left, inset). A similar voltage pulse protocol was applied to generate Ca²⁺ current traces from basal SGNs (right, inset). Peak Ca²⁺ current density–voltage relations for apical (•) and basal (○) SGNs. At voltages (−10–10 mV), there were significant differences between apical and basal Ca²⁺ current densities (*p < 0.05; n = 17). B, The DHP antagonist, nimodipine, blocks a component of whole-cell Ca²⁺ currents in SGNs. Current traces recorded from neurons isolated from apical [top, inset (control); bottom, inset (nimodipine)] segments of the cochlea. Perfusion of external solution containing 10 μm nimodipine resulted in a reduction of the Ca²⁺ currents. The corresponding current density–voltage relations for apical (B) and basal (C) SGNs (n = 9). The control data are illustrated with black lines and symbols and the residual current after nimodipine block is shown in blue lines and symbols. D–I, The current density–voltage relations were generated before (black lines and symbols) and after (blue lines and symbols) application of Ca²⁺ current blockers: rSNX-482 for R-type currents (D, E); ATX for P/Q-type currents (F, G); and CTX for N-type currents (H, I). D, E, Current density–voltage relations for control (black) and the remaining current density after application of toxins (blue) for apical (D) and basal (E) SGNs (n = 6). The insets in the left panels of the plots are representative current traces recorded from a holding voltage of −70 mV to a step voltage of 0 mV. F, G, Similar data obtained upon recording control Ca²⁺ currents and after application of the P/Q-type Ca²⁺ current blocker, 1 μm ATX. H, I, Summary data of the effects of the N-type Ca²⁺ channel blocker on apical versus basal neurons. Table 1 illustrates the summary data for the effects of Ca²⁺ channel blockers on whole-cell Ca²⁺ currents.