Kvbeta1.1 associates with Kvalpha1.4 in Chinese hamster ovary cells and pigeon type II vestibular hair cells and enhances the amplitude, inactivation and negatively shifts the steady-state inactivation range

Electrophysiological properties of vestibular hair cells isolated from human crista

Introduction

The vast majority of cellular studies on mammalian vestibular hair cells have been carried out in rodent models due in part to the inaccessibility of human inner ear organs and reports describing electrophysiological recordings from human inner ear sensory hair cells are scarce. Here, we obtained freshly harvested vestibular neuroepithelia from adult translabyrinthine surgical patients to obtain electrophysiological recordings from human hair cells.

Methods

Whole cell patch clamp recordings were performed on hair cells mechanically isolated from human cristae to characterize voltage-dependent and pharmacological properties of membrane currents. Hair cells were classified as type I or type II according to morphological characteristics and/or their electrophysiological properties.

Results

Type I hair cells exhibited low voltage-activated K+ currents (IKLV) at membrane potentials around the mean resting membrane potential (-63 mV) and large slowly activating outward K+ currents in response to depolarizing voltage steps. Recordings from type II hair cells revealed delayed rectifier type outward K+ currents that activated above the average resting potential of -55 mV and often showed some inactivation at more depolarized potentials. Perfusion with the K+ channel blocker 4-aminopyridine (1 mM) substantially reduced outward current in both hair cell types. Additionally, extracellular application of 8-bromo-cGMP inhibited IKLV in human crista type I hair cells suggesting modulation via a nitric oxide/cGMP mechanism. A slow hyperpolarization-activated current (Ih) was observed in some hair cells in response to membrane hyperpolarization below -100 mV.

Discussion

In summary, whole cell recordings from isolated human hair cells revealed ionic currents that strongly resemble mature current phenotypes previously described in hair cells from rodent vestibular epithelia. Rapid access to surgically obtained adult human vestibular neuroepithelia allows translational studies crucial for improved understanding of human peripheral vestibular function.

Pimozide Inhibits Type II but Not Type I Hair Cells in Chicken Embryo and Adult Mouse Vestibular Organs

BACKGROUND

Pimozide is a conventional antipsychotic drug of the diphenylbutylpiperidine class, widely used for treating schizophrenia and delusional disorders and for managing motor and phonic tics in Tourette's syndrome. Pimozide is known to block dopaminergic D2 receptors and various types of voltage-gated ion channels. Among its side effects, dizziness and imbalance are the most frequently observed, which may imply an effect of the drug on the vestibular sensory receptors, the hair cells. Amniotes possess two classes of vestibular hair cells, named type I and type II hair cells, which differ in terms of signal processing and transmission. We previously reported that Pimozide [3 μM] significantly increased a delayed outward rectifying K+ current (IK,V).

METHODS AND RESULTS

In the present study, using the whole-cell patch-clamp technique we additionally show that Pimozide decreases the inward rectifying K+ current (IK,1) and the mixed Na+/K+ current (Ih) of chicken embryo type II hair cells, whereas it does not affect type I hair cells' ionic currents. Since ion channels' expression can vary depending on age and animal species, in the present study, we also tested Pimozide in adult mouse vestibular hair cells. We found that, like in the chicken embryo, Pimozide significantly increases IK,V and decreases IK,1 and Ih in type II hair cells. However, in the adult mouse, Pimozide also slightly increased the outward rectifying K+ current in type I hair cells.

CONCLUSIONS

While providing a possible explanation for the vestibular side effects of Pimozide in humans, its inhibitory action on mammalian hair cells might be of interest for the local treatment of vestibular disorders characterized by altered vestibular input, like Ménière's disease.

The potassium channel subunit KV1.8 (Kcna10) is essential for the distinctive outwardly rectifying conductances of type I and II vestibular hair cells

In amniotes, head motions and tilt are detected by two types of vestibular hair cells (HCs) with strikingly different morphology and physiology. Mature type I HCs express a large and very unusual potassium conductance, gK,L, which activates negative to resting potential, confers very negative resting potentials and low input resistances, and enhances an unusual non-quantal transmission from type I cells onto their calyceal afferent terminals. Following clues pointing to KV1.8 (Kcna10) in the Shaker K channel family as a candidate gK,L subunit, we compared whole-cell voltage-dependent currents from utricular HCs of KV1.8-null mice and littermate controls. We found that KV1.8 is necessary not just for gK,L but also for fast-inactivating and delayed rectifier currents in type II HCs, which activate positive to resting potential. The distinct properties of the three KV1.8-dependent conductances may reflect different mixing with other KV subunits that are reported to be differentially expressed in type I and II HCs. In KV1.8-null HCs of both types, residual outwardly rectifying conductances include KV7 (Knq) channels. Current clamp records show that in both HC types, KV1.8-dependent conductances increase the speed and damping of voltage responses. Features that speed up vestibular receptor potentials and non-quantal afferent transmission may have helped stabilize locomotion as tetrapods moved from water to land.

The potassium channel subunit KV1.8 (Kcna10) is essential for the distinctive outwardly rectifying conductances of type I and II vestibular hair cells

In amniotes, head motions and tilt are detected by two types of vestibular hair cells (HCs) with strikingly different morphology and physiology. Mature type I HCs express a large and very unusual potassium conductance, gK,L, which activates negative to resting potential, confers very negative resting potentials and low input resistances, and enhances an unusual non-quantal transmission from type I cells onto their calyceal afferent terminals. Following clues pointing to KV1.8 (KCNA10) in the Shaker K channel family as a candidate gK,L subunit, we compared whole-cell voltage-dependent currents from utricular hair cells of KV1.8-null mice and littermate controls. We found that KV1.8 is necessary not just for gK,L but also for fast-inactivating and delayed rectifier currents in type II HCs, which activate positive to resting potential. The distinct properties of the three KV1.8-dependent conductances may reflect different mixing with other KV subunits that are reported to be differentially expressed in type I and II HCs. In KV1.8-null HCs of both types, residual outwardly rectifying conductances include KV7 (KCNQ) channels. Current clamp records show that in both HC types, KV1.8-dependent conductances increase the speed and damping of voltage responses. Features that speed up vestibular receptor potentials and non-quantal afferent transmission may have helped stabilize locomotion as tetrapods moved from water to land.

Comparative biology of the amniote vestibular utricle

The sensory epithelia of the auditory and vestibular systems of vertebrates have shared developmental and evolutionary histories. However, while the auditory epithelia show great variation across vertebrates, the vestibular sensory epithelia appear seemingly more conserved. An exploration of the current knowledge of the comparative biology of the amniote utricle, a vestibular sensory epithelium that senses linear acceleration, shows interesting instances of variability between birds and mammals. The distribution of sensory hair cell types, the position of the line of hair bundle polarity reversal and the properties of supporting cells show marked differences, likely impacting vestibular function and hair cell regeneration potential.