Voltage-dependent currents in isolated vestibular afferent calyx terminals.
Na(+) currents were studied by whole cell patch clamp of chalice-shaped afferent terminals attached to type I hair cells isolated from the gerbil semicircular canal and utricle. Outward K(+) currents were blocked with intracellular Cs(+) or with extracellularly applied 20 microM linopirdine and 2.5 mM 4-aminopyridine (4-AP). With K(+) currents blocked, inward currents activated and inactivated rapidly, had a maximum mean peak amplitude of 0.92 +/- 0.60 (SD) nA (n = 24), and activated positive to -60 mV from holding potentials of -70 mV and more negative. The transient inward currents were blocked almost completely by 100 nM TTX, confirming their identity as Na(+) currents. Half-inactivation of Na(+) currents occurred at -82.6 +/- 0.9 mV, with a slope factor of 9.2 +/- 0.8 (n = 7) at room temperature. In current clamp, large overshooting action potential-like events were observed only after prior hyperpolarizing current injections. However, spontaneous currents consistent with quantal release from the hair cell were observed at holding potentials close to the zero-current potential. This is the first report of ionic conductances in calyx terminals postsynaptic to type I hair cells in the mammalian vestibular system.
Rennie
Katherine J
KJ
Department of Otolaryngology, University of Colorado at Denver and Health Sciences Center, 4200 E. Ninth Ave. B205, Denver, CO 80262, USA. katie.rennie@uchsc.edu
Streeter
Michele A
MA
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D005849:Gerbillinae; D018069:Hair Cells, Vestibular / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000502:physiology*; D014722:Vestibule, Labyrinth / Q000502:physiology*
D024642:Potassium Channels, Voltage-Gated; D015222:Sodium Channels; D012964:Sodium; D011188:Potassium