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.

Developmental Changes in Two Voltage-Dependent Sodium Currents in Utricular Hair Cells

“…I Na,1 of rat utricular hair cells resembles the current reported in immature mouse utricular hair cells by Rüsch and Eatock (1997) and Géléoc et al (2004) and in rat cochlear outer hair cells by Oliver et al (1997). I Na,2 resembles the TTX-sensitive current reported in immature rat utricular hair cells by Chabbert et al (2003) and Lennan et al (1999) and in immature mouse cochlear inner hair cells by Marcotti et al (2003).…”

Regional Analysis of Whole Cell Currents From Hair Cells of the Turtle Posterior Crista

“…As was previously reported in other preparations (Correia and Lang 1990;Griguer et al 1993a,b;Holt et al 1999;Lennan et al 1999;Masetto et al 2000;Rennie and Correia 1994;Rüsch and Eatock 1996;Rüsch et al 1998), type I and II hair cells differ in their electrophysiology. There are differences in both outwardly and inwardly rectifying currents, which we consider in turn.…”

“…We never encountered the reverse situation, in which an instantaneous component developed only after prolonged recording. Such observations, which have also been made in mammals (Chen and Eatock 2000;Hurley and Eatock 1999), would seem inconsistent with the suggestion that the hyperpolarized activation range of type I cells reflects the washout of normal intracellular constituents during whole cell recording (Lennan et al 1999). Other evidence (see following text) supports the contention that virtually all type I hair cells have I K,L whether or not they have the instantaneous current.…”

Development of K+ and Na+ conductances in rodent postnatal semicircular canal type I hair cells

“…Inward currents were not present when choline was substituted for external Na ϩ (data not shown), confirming their identity as Na ϩ currents (I Na ). Transient Na ϩ currents have also been described previously in rat and mouse immature utricular hair cells (14,19,35). The I-V plot in Fig.…”

“…We found a rapidly activating, rapidly inactivating inward Na ϩ current in postnatal SCC rat and gerbil hair cells. A transient sodium current, I Na , has been described previously in hair cells from mouse and rat utricle (2,14,19,35), mouse, rat and guinea pig cochlea (20,24,34) and chicken vestibular system (23,33). In mouse utricle I Na peaked at E16 -E18 and subsequently declined to almost zero at birth (14).…”