title: Potassium accumulation between type I hair cells and calyx terminals in mouse crista.
abstract: The mode of synaptic transmission in the vestibular periphery, between type I hair cells and their associated calyx terminal, has been the subject of much debate. The close and extensive apposition of pre- and post-synaptic elements has led some to suggest potassium (K(+)) accumulates in the intercellular space and even plays a role in synaptic transmission. During patch clamp recordings from isolated and embedded hair cells in a semi-intact preparation of the mouse cristae, we noted marked differences in whole-cell currents. Embedded type I hair cells show a prominent droop during steady-state activation as well as a dramatic collapse in tail currents. Responses to a depolarizing voltage step (-124 to +16 mV) in embedded, but not isolated, hair cells resulted in a >40 mV shift of the K(+) equilibrium potential and a rise in effective K(+) concentration (>50 mM) in the intercellular space. Together these data suggest K(+) accumulation in the intercellular space accounts for the different responses in isolated and embedded type I hair cells. To test this notion, we exposed the preparation to hyperosmotic solutions to enlarge the intercellular space. As predicted, the K(+) accumulation effects were reduced; however, a fit of our data with a classic diffusion model suggested K(+) permeability, rather than the intercellular space, had been altered by the hyperosmotic change. These results support the notion that under depolarizing conditions substantial K(+) accumulation occurs in the space between type I hair cells and calyx. The extent of K(+) accumulation during normal synaptic transmission, however, remains to be determined.
authors.affiliation: School of Biomedical Sciences & Pharmacy, Faculty of Health, The University of Newcastle, and Hunter Medical Research Institute, Callaghan, NSW, 2308, Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Lim
authors.forename: Angela E
authors.initials: AE
authors.lastname: Kindig
authors.forename: Scott W
authors.initials: SW
authors.lastname: Donne
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Callister
authors.forename: Alan M
authors.initials: AM
authors.lastname: Brichta
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics / Q000379:methods; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D018069:Hair Cells, Vestibular / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques / Q000379:methods; D011188:Potassium / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D019063:Tenascin / Q000378:metabolism; D014722:Vestibule, Labyrinth / Q000166:cytology*
chemical_list: D019063:Tenascin; D011188:Potassium