Electrophysiological Properties of Vestibular Sensory and Supporting Cells in the Labyrinth Slice Before and During Regeneration

Abstract

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 ap...

Hyperpolarization-Activated Current (I h) in Vestibular Calyx Terminals: Characterization and Role in Shaping Postsynaptic Events

“…Cs + can also block the K + -selective inward rectifier current, I Kir , which has rapid activation and inactivation kinetics. I Kir was reported in pigeon semicircular hair cells and supporting cells (Masetto and Correia 1997) and in mouse utricular hair cells (Rüsch and Eatock 1996). In vestibular ganglion cells Ba 2+ , which blocks I Kir but not I h , abolished an early portion of the hyperpolarization-activated current, suggesting a contribution from I Kir (Chabbert et al 2001b).…”

“…Within the vestibular periphery I h has been found in hair cells of the frog sacculus, where it was speculated to play a role in restoring the resting potential after hyperpolarizations (Holt and Eatock 1995), bird semicircular canal (Masetto and Correia 1997;Masetto et al 2000), and mouse utricle (Horwitz et al 2011). Immunolabeling detected HCN1 in the basolateral region of hair cells and HCN2 and HCN4 in other neuroepithelial cells of the mouse utricle (Horwitz et al 2010(Horwitz et al , 2011.…”

Developmental Acquisition of Voltage-Dependent Conductances and Sensory Signaling in Hair Cells of the Embryonic Mouse Inner Ear

“…Because a systematic variation in single-channel conductance as a function of age is unlikely, the parsimonious interpretation suggests that the increased density results from an increase in the number of functional potassium channels. Therefore, we suggest that the data can be best explained by the developmental acquisition of a homogeneous variety of voltage-dependent potassium channels with properties similar to the delayed rectifier seen in mature postnatal type II hair cells (Lang and Correia, 1989;Rennie and Ashmore, 1991;Masetto and Correia, 1997;Rüsch et al, 1998;Masetto et al, 2000;Brichta et al, 2002). However, we cannot exclude the possibility that the channels consist of a consistent ratio of heterogeneous channel subunits whose stoichiometry is tightly regulated.…”

Regeneration of Vestibular Otolith Afferents after Ototoxic Damage

“…For example, ototoxic antibiotics produce vestibular sensory cell death and receptor denervation (Berg, 1951;Wersäll and Hawkins, 1962;Lindeman, 1969a,b), followed by severe dysfunction (Wersäll and Hawkins, 1962;Carey et al, 1996Carey et al, , 2002Goode et al, 1999;Hirvonen et al, 2005). It is now firmly established that cochlear and vestibular sensory hair cells spontaneously regenerate after damage in fish, amphibians, and birds (Corwin and Cotanche, 1988;Rubel, 1992, 1993;Baird et al, 1993), and these regenerated hair cells are contacted by new afferent and efferent terminals (Ryals and Westbrook, 1994;Masetto and Correia, 1997b;Hennig and Cotanche, 1998). In addition, functional recovery of vestibular hair cells (Masetto and Correia, 1997a), afferent sensitivity to motion (Li and Correia, 1998;Boyle et al, 2002), and vestibular behavioral responses (Jones and Nelson, 1992;Carey et al, 1996;Goode et al, 1999;Dickman and Lim, 2004) all correlate with regenerative development in birds.…”