title: Developmental expression of BK channels in chick cochlear hair cells.
abstract: BACKGROUND
  Cochlear hair cells are high-frequency sensory receptors. At the onset of hearing, hair cells acquire fast, calcium-activated potassium (BK) currents, turning immature spiking cells into functional receptors. In non-mammalian vertebrates, the number and kinetics of BK channels are varied systematically along the frequency-axis of the cochlea giving rise to an intrinsic electrical tuning mechanism. The processes that control the appearance and heterogeneity of hair cell BK currents remain unclear.
  
  
  RESULTS
  Quantitative PCR results showed a non-monotonic increase in BK alpha subunit expression throughout embryonic development of the chick auditory organ (i.e. basilar papilla). Expression peaked near embryonic day (E) 19 with six times the transcript level of E11 sensory epithelia. The steady increase in gene expression from E11 to E19 could not explain the sudden acquisition of currents at E18-19, implicating post-transcriptional mechanisms. Protein expression also preceded function but progressed in a sequence from diffuse cytoplasmic staining at early ages to punctate membrane-bound clusters at E18. Electrophysiology data confirmed a continued refinement of BK trafficking from E18 to E20, indicating a translocation of BK clusters from supranuclear to subnuclear domains over this critical developmental age.
  
  
  CONCLUSIONS
  Gene products encoding BK alpha subunits are detected up to 8 days before the acquisition of anti-BK clusters and functional BK currents. Therefore, post-transcriptional mechanisms seem to play a key role in the delayed emergence of calcium-sensitive currents. We suggest that regulation of translation and trafficking of functional alpha subunits, near voltage-gated calcium channels, leads to functional BK currents at the onset of hearing.
authors.affiliation: University of Illinois at Chicago, USA. yli71@uic.edu
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Graham M
authors.initials: GM
authors.lastname: Atkin
authors.forename: Marti M
authors.initials: MM
authors.lastname: Morales
authors.forename: Li Qian
authors.initials: LQ
authors.lastname: Liu
authors.forename: Mingjie
authors.initials: M
authors.lastname: Tong
authors.forename: R Keith
authors.initials: RK
authors.lastname: Duncan
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics / Q000378:metabolism*; D002642:Chick Embryo; D003051:Cochlea / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental; D006198:Hair Cells, Auditory / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational
chemical_list: D030161:Avian Proteins; D051036:Large-Conductance Calcium-Activated Potassium Channels