Potassium currents in mammalian and avian isolated type I semicircular canal hair cells

Abstract

1. Type I vestibular hair cells were isolated from the cristae ampullares of the semicircular canals of the Mongolian gerbil (Meriones unguiculatus) and the white king pigeon (Columba livia). Dissociated type I cells were distinguished from type II hair cells by their neck to plate ratio (NPR) and their characteristic amphora shape. 2. The membrane properties of gerbil and pigeon type I hair cells were studied in whole-cell voltage- and current-clamp using the perforated patch technique with amphotericin B as the perforating agent. 3. In whole-cell current-clamp, the average zero-current potential, Vz, measured for pigeon type I hair cells, was -70 +/- 7 (SD) mV (n = 18) and -71 +/- 11 mV (n = 83) for gerbil type I hair cells. 4. At Vz, for both gerbil and pigeon type I hair cells, a potassium current (IKI) was > or = 50% activated. This current deactivated rapidly when the membrane potential was hyperpolarized below -90 mV. 5. IKI was blocked by externally applied 4-aminopyridine (4-AP) (5 mM) and by internally applied 20 mM tetraethylammonium (TEA). It was also reduced when 4 mM barium was present in the external solution. The degree of block by barium increased as the membrane potential became more positive. External cesium (5 mM) blocked the inward component of IKI. When IKI was pharmacologically blocked, Vz depolarized by approximately 40 mV. Therefore IKI appears to be a delayed rectifier and to set the more negative Vz noted for isolated type I hair cells when compared to isolated type II hair cells, which do not have IKI. 6. A second, smaller potassium current was present at membrane potential depolarizations above -40 mV. This current was blocked by 30-50 mM, externally applied TEA, 100 microM quinidine, 100 nM apamin, but not 100 nM charybdotoxin, indicating that this is a calcium-activated potassium current, IK(Ca), different from the maxi-K calcium-activated potassium current found in most other hair cells.

Developmental Acquisition of Voltage-Dependent Conductances and Sensory Signaling in Hair Cells of the Embryonic Mouse Inner Ear

“…In postnatal vestibular epithelia, expression of G K,L is highly correlated with type I hair cells (Correia and Lang, 1990;Rennie and Correia, 1994;Ricci et al, 1996;Rüsch and Eatock, 1996;Rüsch et al, 1998). We found no evidence of G K,L in the 44 cells examined at stages earlier than E18 (Fig.…”

“…We were surprised to note that 28 of 82 E18 to P2 cells revealed evidence of a conductance with striking similarity to the lowvoltage-activated potassium conductance, known as G K,L in mouse hair cells (Rüsch and Eatock, 1996;Rüsch et al, 1998;Chen and Eatock, 2000) and G K1 in avian hair cells (Correia and Lang, 1990;Rennie and Correia, 1994). Previous reports suggested that G K,L was present only at P4 and later stages (Rüsch et al, 1998).…”

Modulation of Voltage-Gated Ca2+Current in Vestibular Hair Cells by Nitric Oxide

“…In the vestibular endorgans one of the targets proposed for NO is the low-threshold K ϩ current (I K,L ) expressed in type I hair cells (Rennie and Correia 1994;Rüsch and Eatock 1996a,b). Behrend et al (1997) found that the cGMP and its membrane-permeant 8-Br-cGMP analog inhibit I K,L .…”

Regeneration of Vestibular Otolith Afferents after Ototoxic Damage

“…In addition, only hair cells with a type II morphologic phenotype were observed to develop in the epithelium, even in the striolar region in which type I hair cells typically predominate in normal adult maculas. Classically, discrimination between type I and type II vestibular hair cells in normal adult tissue has been based on morphology (Wersäll, 1956;Lysakowski and Goldberg, 1997;Rüsch et al, 1998), innervations (Kevetter et al, 1994;Lysakowski and Goldberg, 1997), and channel properties (Correia and Lang, 1990;Eatock et al, 1994;Rennie and Correia, 1994;Ricci et al, 1996;Rüsch et al, 1998). Mature type II hair cells are innervated by bouton terminals and type I hair cells are enclosed by a calyceal terminal.…”