Extracellular polarization of the hair cells produced a transverse motion of the

tectorial membrane toward the neural limb (Figures 7B and 7C). Venetoclax molecular weight A mean negative displacement of beads of 24 ± 16 nm (range 10 to 56 nm; d = 0.36–0.51) was achieved in eight preparations using 100 μA current flowing from the abneural to neural electrodes. These measurements were made on beads located above SHCs and, by focusing through the tectorial membrane, it was possible also to image the bundles ( Figures 7A and 7B). Comparison of the relative displacement of the hair bundle to that of beads lying directly above the bundle indicated that the bundle moved slightly more than the selleck screening library bead ( Figure 7B). The ratio of the bundle to bead displacement for the same polarization was 1.45 ± 1.1 (n = 5), though this is not significantly different from 1 (two-tailed Students t test, p = 0.2), suggesting a tight coupling of the bundles to the tectorial membrane. Tectorial membrane

motion in response to extracellular stimulation was also monitored over the THCs, the mean negative displacement being 25 ± 22 nm (n = 4). The displacements obtained by extracellular polarization were similar to those elicited from individual SHCs in that they were reversibly blocked by 10 mM Na+ salicylate (Figure 7C). This reversible block, shown in four preparations, makes it unlikely that lateral movements produced by extracellular currents stemmed from a direct electrophoretic motion of the tectorial membrane. The dose-response relationship for the action of salicylate on the voltage-evoked movements (Figures 7D and 7E) was fit with a Hill equation with a half-blocking concentration of 3.6 mM, similar to that in OHCs (Tunstall et al., 1995).

In order to ascertain whether the bundle movements were elicited over the same range of membrane potentials as those seen in individual SHCs, we estimated the membrane depolarization evoked by extracellular polarization. To do this, SHCs were patch clamped in a preparation in which the all tectorial membrane had been removed but which was stimulated by extracellular current polarization (Figure 7F). The change in membrane potential increased with the current polarization, as did the size of the hair bundle movement. In multiple SHC recordings, the depolarization (measured in current clamp) was proportional to the magnitude of the external current from 40 to 100 μA, with a proportionality constant of 0.74 mV/μA. If extracellular current stimuli are as effective in the presence of the tectorial membrane, the 100 μA polarization routinely used would depolarize the SHCs to ∼20 mV assuming they have a resting potential of about −55 mV in perilymph (Tan et al., 2013).