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Electrophysiological properties of vestibular sensory and supporting cells in the labyrinth slice before and during regeneration.

The whole cell patch-clamp technique in combination with the slice preparation was used to investigate the electrophysiological properties of pigeon semicircular canal sensory and supporting cells. These properties were also characterized in regenerating neuroepithelia of pigeons preinjected with streptomycin to kill the hair cells. Type II hair cells from each of the three semicircular canals showed similar, topographically related patterns of passive and active membrane properties. Hair cells located in the peripheral regions (zone I, near the planum semilunatum) had less negative resting potentials [0-current voltage in current-clamp mode (Vz) = -62.8 +/- 8.7 mV, mean +/- SD; n = 13] and smaller membrane capacitances (Cm = 5.0 +/- 0.9 pF, n = 14) than cells of the intermediate (zone II; Vz = -79.3 +/- 7.5 mV, n = 3; Cm = 5.9 +/- 1.2 pF, n = 4) and central (zone III; Vz = -68.0 +/- 9.6 mV, n = 17; Cm = 7.1 +/- 1.5 pF, n = 18) regions. In peripheral hair cells, ionic currents were dominated by a rapidly activating/inactivating outward K+ current, presumably an A-type K+ current (IKA). Little or no inwardly rectifying current was present in these cells. Conversely, ionic currents of central hair cells were dominated by a slowly activating/inactivating outward K+ current resembling a delayed rectifier K+ current (IKD). Moreover, an inward rectifying current at voltages negative to -80 mV was present in all central cells. This current was composed of two components: a slowly activating, noninactivating component (Ih), described in photoreceptors and saccular hair cells, and a faster-activating, partially inactivating component (IK1) also described in saccular hair cells in some species. Ih and IK1 were sometimes independently expressed by hair cells. Hair cells located in the intermediate region (zone II) had ionic currents more similar to those of central hair cells than peripheral hair cells. Outward currents in intermediate hair cells activated only slightly more quickly than those of the cells of the central region, but much more slowly than those of the peripheral cells. Additionally, intermediate hair cells, like central hair cells, always expressed an inward rectifying current. The regional distribution of outward rectifying potassium conductances resulted in macroscopic currents differing in peak-to-steady state ratio. We quantified this by measuring the peak (Gp) and steady-state (Gs) slope conductance in the linear region of the current-voltage relationship (-40 to 0 mV) for the hair cells located in the different zones. Gp/Gs average values (4.1 +/- 2.1, n = 15) from currents in peripheral hair cells were higher than those from intermediate hair cells (2.3 +/- 0.8, n = 4) and central hair cells(1.9 +/- 0.8, n = 21). The statistically significant differences (P < 0.001) in Gp/Gs ratios could be accounted for by KA channels being preferentially expressed in peripheral hair cells. Hair cell electrophysiological properties in animals pretreated with streptomycin were investigated at approximately 3 wk and approximately 9-10 wk post injection sequence (PIS). At 3 wk PIS, hair cells (all zones combined) had a statistically significantly (P < 0.001) lower Cm (4.6 +/- 1.1 pF, n = 24) and a statistically significantly (P < 0.01) lower Gp(48.4 +/- 20.8 nS, n = 26) than control animals (Cm = 6.2 +/- 1.6 pF, n = 36; Gp = 66 +/- 38.9 nS, n = 40). Regional differences in values of Vz, as well as the distribution of outward and inward rectifying currents, seen in control animals, were still obvious. But, differences in the relative contribution of the expression of the different ionic current components changed. This result could be explained by a relative decrease in IKA compared with IKD during that interval of regeneration, which was particularly evident in peripheral hair cells. (ABSTRACT TRUNCATED)