title: Ionic currents and current-clamp depolarisations of type I and type II hair cells from the developing rat utricle.
abstract: Ionic currents and the voltage response to injected currents were studied in an acutely dissected preparation of the rat utricle between birth and postnatal day 12 (PN12). Based upon morphological criteria, the sensory cells examined were divided into two classes, "type I" and "type 2 category," the latter of which may include some immature type I cells. The former group comprises a clearly defined electrophysiological population, with one large outwardly rectifying potassium conductance that is sensitive to 4-aminopyridine (4-AP), insensitive to tetraethylammonium (TEA) and displays voltage-dependent activation kinetics. In the absence of enzymatic dissociation procedures, and with the epithelium left largely intact, the mean half activation of this conductance was -30.3 mV at PN3, and -37.5 mV at PN12. At both stages it was almost entirely turned off at -74 mV. Omission of ATP from the intracellular solution appeared to prevent rundown of this conductance. Type II category hair cells formed a more heterogeneous population, exhibiting a distinct TEA-sensitive delayed rectifier potassium conductance; the rapidly activating and inactivating IA; an inward rectifier; and inward sodium currents at around PN3. Both cell types depolarised strongly in response to injected currents, with time courses reflecting the activation kinetics of their major outward conductances.
authors.affiliation: INSERM Unité 432, Neurobiologie et Développement du Système Vestibulaire, Université Montpellier II, Place Eugène Bataillon F-34095 Montpellier, France. Glennan@crit.univ-montp2.fr
authors.forename: G W
authors.initials: GW
authors.lastname: Lennan
authors.forename: A
authors.initials: A
authors.lastname: Steinacker
authors.forename: J
authors.initials: J
authors.lastname: Lehouelleur
authors.forename: A
authors.initials: A
authors.lastname: Sans
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D004594:Electrophysiology; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D012444:Saccule and Utricle / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D015222:Sodium Channels; D019789:Tetraethylammonium; D015761:4-Aminopyridine