SK Current, Expressed During the Development and Regeneration of Chick Hair Cells, Contributes to the Patterning of Spontaneous Action Potentials.

Snezana Levic

doi:10.3389/fncel.2021.766264

Abstract

Chick hair cells display calcium (Ca2+)-sensitive spontaneous action potentials during development and regeneration. The role of this activity is unclear but thought to be involved in establishing proper synaptic connections and tonotopic maps, both of which are instrumental to normal hearing. Using an electrophysiological approach, this work investigated the functional expression of Ca2+-sensitive potassium [IK(Ca)] currents and their role in spontaneous electrical activity in the developing and regenerating hair cells (HCs) in the chick basilar papilla. The main IK(Ca) in developing and regenerating chick HCs is an SK current, based on its sensitivity to apamin. Analysis of the functional expression of SK current showed that most dramatic changes occurred between E8 and E16. Specifically, there is a developmental downregulation of the SK current after E16. The SK current gating was very sensitive to the availability of intracellular Ca2+ but showed very little sensitivity to T-type voltage-gated Ca2+ channels, which are one of the hallmarks of developing and regenerating hair cells. Additionally, apamin reduced the frequency of spontaneous electrical activity in HCs, suggesting that SK current participates in patterning the spontaneous electrical activity of HCs.

Highlights

The auditory system of the chicken has been extensively used in comparative studies of the evolution and development of hearing (Carr and Code, 2000)
To investigate the presence of IK(Ca) in developing longitudinal middle section chick, Tall hair cells (THCs) whole-cell currents were elicited by 250 ms depolarizing voltage steps in 10-mV increments from a holding potential of −90 mV
These findings strongly suggest that SK current has a pivotal role in the patterning of electrical activity, which may have an instructional role during the development and regeneration of hair cells (HCs) (Figures 2, 8)

Summary

Introduction

The auditory system of the chicken has been extensively used in comparative studies of the evolution and development of hearing (Carr and Code, 2000). The auditory systems of both humans and chickens are at comparable stages at birth, partially but not fully developed (Jackson and Rubel, 1978). Both species start to hear in the second-third of the gestation period (Jackson and Rubel, 1978; Birnholz and Bean, 1983), making the chick cochlea an attractive model system to study the developmental mechanisms of hair cells (HCs). SHCs exhibit limited motility, suggesting that this may be one of the mammalian specializations enabling high-frequency hearing (He et al, 2003, 2014; Schaechinger and Oliver, 2007; Beurg et al, 2013)

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