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

The turtle posterior crista is made up of two hemicristae, each consisting of a central zone containing type I and type II hair cells and a surrounding peripheral zone containing only type II hair cells and extending from the planum semilunatum to the nonsensory torus. Afferents from various regions of a hemicrista differ in their discharge properties. To see if afferent diversity is related to the basolateral currents of the hair cells innervated, we selectively harvested type I and II hair cells from the central zone and type II hair cells from two parts of the peripheral zone, one near the planum and the other near the torus. Voltage-dependent currents were studied with the whole cell, ruptured-patch method and characterized in voltage-clamp mode. We found regional differences in both outwardly and inwardly rectifying voltage-sensitive currents. As in birds and mammals, type I hair cells have a distinctive outwardly rectifying current ( IK,L), which begins activating at more hyperpolarized voltages than do the outward currents of type II hair cells. Activation of IK,Lis slow and sigmoidal. Maximal outward conductances are large. Outward currents in type II cells vary in their activation kinetics. Cells with fast kinetics are associated with small conductances and with partial inactivation during 200-ms depolarizing voltage steps. Almost all type II cells in the peripheral zone and many in the central zone have fast kinetics. Some type II cells in the central zone have large outward currents with slow kinetics and little inactivation. Although these currents resemble IK,L, they can be distinguished from the latter both electrophysiologically and pharmacologically. There are two varieties of inwardly rectifying currents in type II hair cells: activation of IK1is rapid and monoexponential, whereas that of Ihis slow and sigmoidal. Many type II cells either have both inward currents or only have IK1; very few cells only have Ih. Inward currents are less conspicuous in type I cells. Type II cells near the torus have smaller outwardly rectifying currents and larger inwardly rectifying currents than those near the planum, but the differences are too small to account for variations in discharge properties of bouton afferents innervating the two regions of the peripheral zone. The large outward conductances seen in central cells, by lowering impedances, may contribute to the low rotational gains of some central-zone afferents.

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Morphological Identification of Physiologically Characterized Afferents Innervating the Turtle Posterior Crista

Journal of Neurophysiology ◽

10.1152/jn.2000.83.3.1202 ◽

2000 ◽

Vol 83 (3) ◽

pp. 1202-1223 ◽

Cited By ~ 44

Author(s):

Alan M. Brichta ◽

Jay M. Goldberg

Keyword(s):

Hair Cells ◽

Central Zone ◽

Peripheral Zone ◽

Morphological Identification ◽

Type I ◽

Type Ii ◽

Response Dynamics ◽

Multivariate Statistical ◽

Class B ◽

Longitudinal Position

The turtle posterior crista consists of two hemicristae. Each hemicrista extends from the planum semilunatum to the nonsensory torus and includes a central zone (CZ) surrounded by a peripheral zone (PZ). Type I and type II hair cells are found in the CZ and are innervated by calyx, dimorphic and bouton afferents. Only type II hair cells and bouton fibers are found in the PZ. Units were intraaxonally labeled in a half-head preparation. Bouton (B) units could be near the planum (BP), near the torus (BT), or in midportions of a hemicrista, including the PZ and CZ. Discharge properties of B units vary with longitudinal position in a hemicrista but not with morphological features of their peripheral terminations. BP units are regularly discharging and have small gains and small phase leads re angular head velocity. BT units are irregular and have large gains and large phase leads. BM units have intermediate properties. Calyx (C) and dimorphic (D) units have similar discharge properties and were placed into a single calyx-bearing (CD) category. While having an irregular discharge resembling BT units, CD units have gains and phases similar to those of BM units. Rather than any single discharge property, it is the relation between discharge regularity and either gain or phase that makes CD units distinctive. Multivariate statistical formulas were developed to infer a unit's morphological class (B or CD) and longitudinal position solely from its discharge properties. To verify the use of the formulas, discharge properties were compared for units recorded intraaxonally or extracellularly in the half-head or extracellularly in intact animals. Most B units have background rates of 10–30 spikes/s. The CD category was separated into CD-high and CD-low units with background rates above or below 5 spikes/s, respectively. CD-low units have lower gains and phases and are located nearer the planum than CD-high units. In their response dynamics over a frequency range from 0.01–3 Hz, BP units conform to an overdamped torsion-pendulum model. Other units show departures from the model, including high-frequency gain increases and phase leads. The longitudinal gradient in the physiology of turtle B units resembles a similar gradient in the anamniote crista. In many respects, turtle CD units have discharge properties resembling those of calyx-bearing units in the mammalian central zone.

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Hair-cell counts and afferent innervation patterns in the cristae ampullares of the squirrel monkey with a comparison to the chinchilla

Journal of Neurophysiology ◽

10.1152/jn.1995.73.3.1253 ◽

1995 ◽

Vol 73 (3) ◽

pp. 1253-1269 ◽

Cited By ~ 73

Author(s):

C. Fernandez ◽

A. Lysakowski ◽

J. M. Goldberg

Keyword(s):

Squirrel Monkey ◽

Hair Cells ◽

Central Zone ◽

Peripheral Zone ◽

Nerve Fibers ◽

Type I ◽

Type Ii ◽

Cell Counts ◽

Afferent Fibers ◽

Innervation Patterns

1. The numbers of type I and type II hair cells were estimated by dissector techniques applied to semithin, stained sections of the horizontal, superior, and posterior cristae in the squirrel monkey and the chinchilla. 2. The crista in each species was divided into concentrically arranged central, intermediate, and peripheral zones of equal areas. The three zones can be distinguished by the sizes of individual hair cells and calyx endings, by the density of hair cells, and by the relative frequency of calyx endings innervating single or multiple type I hair cells. 3. In the monkey crista, type I hair cells outnumber type II hair cells by a ratio of almost 3:1. The ratio decreases from 4-5:1 in the central and intermediate zones to under 2:1 in the peripheral zone. For the chinchilla, the ratio is near 1:1 for the entire crista and decreases only slightly between the central and peripheral zones. 4. Nerve fibers supplying the cristae in the squirrel monkey were labeled by extracellular injections of horseradish peroxidase (HRP) into the vestibular nerve. Peripheral terminations of individual fibers were reconstructed and related to the zones of the cristae they innervated and to the sizes of their parent axons. Results were similar for the horizontal, superior, and posterior cristae. 5. Axons seldom bifurcate below the neuroepithelium. Most fibers begin branching shortly after crossing the basement membrane. Their terminal arbors are compact, usually extending no more than 50-100 microns from the parent exon. A small number of long intraepithelial fibers enter the intermediate and peripheral zones of the cristae near its base, then run unbranched for long distances through the neuroepithelium to reach the central zone. 6. There are three classes of afferent fibers innervating the monkey crista. Calyx fibers terminate exclusively on type I hair cells, and bouton fibers end only on type II hair cells. Dimorphic fibers provide a mixed innervation, including calyx endings to type I hair cells and bouton endings to type II hair cells. Long intraepithelial fibers are calyx and dimorphic units, whose terminal fields are similar to those of other fibers. The central zone is innervated by calyx and dimorphic fibers; the peripheral zone, by bouton and dimorphic fibers; and the intermediate zone, by all three kinds of fibers. Internal (axon) diameters are largest for calyx fibers and smallest for bouton fibers. Of the entire sample of 286 labeled fibers, 52% were dimorphic units, 40% were calyx units, and 8% were bouton units.(ABSTRACT TRUNCATED AT 400 WORDS)

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Molecular characterization of an inward rectifier channel (IKir) found in avian vestibular hair cells: cloning and expression of pKir2.1

Physiological Genomics ◽

10.1152/physiolgenomics.00096.2004 ◽

2004 ◽

Vol 19 (2) ◽

pp. 155-169 ◽

Cited By ~ 11

Author(s):

Manning J. Correia ◽

Thomas G. Wood ◽

Deborah Prusak ◽

Tianxiang Weng ◽

Katherine J. Rennie ◽

...

Keyword(s):

Hair Cells ◽

Cho Cells ◽

Dwell Time ◽

Single Channel ◽

Cloning And Expression ◽

Single Type ◽

Type I ◽

Type Ii ◽

Vestibular Hair Cells ◽

Inwardly Rectifying

A fast inwardly rectifying current has been observed in some of the sensory cells (hair cells) of the inner ear of several species. While the current was presumed to be an IKir current, contradictory evidence existed as to whether the cloned channel actually belonged to the Kir2.0 subfamily of potassium inward rectifiers. In this paper, we report for the first time converging evidence from electrophysiological, biochemical, immunohistochemical, and genetic studies that show that the Kir2.1 channel carries the fast inwardly rectifying currents found in pigeon vestibular hair cells. Following cytoplasm extraction from single type II and multiple pigeon vestibular hair cells, mRNA was reverse transcribed, amplified, and sequenced. The open reading frame (ORF), consisting of a 1,284-bp nucleotide sequence, showed 94, 85, and 83% identity with Kir2.1 subunit sequences from chick lens, Kir2 sequences from human heart, and a mouse macrophage cell line, respectively. Phylogenetic analyses revealed that pKir2.1 formed an immediate node with hKir2.1 but not with hKir2.2–2.4. Hair cells (type I and type II) and supporting cells in the sensory epithelium reacted positively with a Kir2.1 antibody. The whole cell current recorded in oocytes and CHO cells, transfected with pigeon hair cell Kir2.1 (pKir2.1), demonstrated blockage by Ba2+ and sensitivity to changing K+ concentration. The mean single-channel linear slope conductance in transfected CHO cells was 29 pS. The open dwell time was long (∼300 ms at −100 mV), and the closed dwell time was short (∼34 ms at −100 mV). Multistates ranging from 3–6 were noted in some single-channel responses. All of the above features have been described for other Kir2.1 channels. Current clamp studies of native pigeon vestibular hair cells illustrated possible physiological roles of the channel and showed that blockage of the channel by Ba2+ depolarized the resting membrane potential by ∼30 mV. Negative currents hyperpolarized the membrane ∼20 mV before block but ∼60 mV following block. RT-PCR studies revealed that the pKir2.1 channels found in pigeon vestibular hair cells were also present in pigeon vestibular nerve, vestibular ganglion, lens, neck muscle, brain (brain stem, cerebellum and optic tectum), liver, and heart.

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Membrane Properties of Chick Semicircular Canal Hair Cells In Situ During Embryonic Development

Journal of Neurophysiology ◽

10.1152/jn.2000.83.5.2740 ◽

2000 ◽

Vol 83 (5) ◽

pp. 2740-2756 ◽

Cited By ~ 31

Author(s):

S. Masetto ◽

P. Perin ◽

A. Malusà ◽

G. Zucca ◽

P. Valli

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Central Zone ◽

Cell Voltage ◽

Peripheral Zone ◽

Membrane Properties ◽

Voltage Response ◽

Type I ◽

Electrophysiological Properties ◽

Different Types

The electrophysiological properties of developing vestibular hair cells have been investigated in a chick crista slice preparation, from embryonic day 10 ( E10) to E21 (when hatching would occur). Patch-clamp whole-cell experiments showed that different types of ion channels are sequentially expressed during development. An inward Ca2+ current and a slow outward rectifying K+current ( I K(V)) are acquired first, at or before E10, followed by a rapid transient K+current ( I K(A)) at E12, and by a small Ca-dependent K+ current ( I KCa) at E14. Hair cell maturation then proceeds with the expression of hyperpolarization-activated currents: a slow I h appears first, around E16, followed by the fast inward rectifier I K1around E19. From the time of its first appearance, I K(A) is preferentially expressed in peripheral ( zone 1) hair cells, whereas inward rectifying currents are preferentially expressed in intermediate ( zone 2) and central ( zone 3) hair cells. Each conductance conferred distinctive properties on hair cell voltage response. Starting from E15, some hair cells, preferentially located at the intermediate region, showed the amphora shape typical of type I hair cells. From E17 (a time when the afferent calyx is completed) these cells expressed I K, L, the signature current of mature type I hair cells. Close to hatching, hair cell complements and regional organization of ion currents appeared similar to those reported for the mature avian crista. By the progressive acquisition of different types of inward and outward rectifying currents, hair cell repolarization after both positive- and negative-current injections is greatly strengthened and speeded up.

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Effects of KCNQ channel blockers on K+ currents in vestibular hair cells

AJP Cell Physiology ◽

10.1152/ajpcell.2001.280.3.c473 ◽

2001 ◽

Vol 280 (3) ◽

pp. C473-C480 ◽

Cited By ~ 29

Author(s):

Katherine J. Rennie ◽

Tianxiang Weng ◽

Manning J. Correia

Keyword(s):

Steady State ◽

Hair Cells ◽

Low Voltage ◽

Dissociation Constants ◽

Channel Blockers ◽

Type I ◽

Type Ii ◽

Kcnq Channels ◽

Vestibular Hair Cells ◽

Inward Currents

Linopirdine and XE991, selective blockers of K+ channels belonging to the KCNQ family, were applied to hair cells isolated from gerbil vestibular system and to hair cells in slices of pigeon crista. In type II hair cells, both compounds inhibited a slowly activating, slowly inactivating component of the macroscopic current recruited at potentials above −60 mV. The dissociation constants for linopirdine and XE991 block were <5 μM. A similar component of the current was also blocked by 50 μM capsaicin in gerbil type II hair cells. All three drugs blocked a current component that showed steady-state inactivation and a biexponential inactivation with time constants of ∼300 ms and 4 s. Linopirdine (10 μM) reduced inward currents through the low-voltage-activated K+ current in type I hair cells, but concentrations up to 200 μM had little effect on steady-state outward K+ current in these cells. These results suggest that KCNQ channels may be present in amniote vestibular hair cells.

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

Journal of Neurophysiology ◽

10.1152/jn.00771.2001 ◽

2002 ◽

Vol 88 (6) ◽

pp. 3279-3292 ◽

Cited By ~ 16

Author(s):

Jay M. Goldberg ◽

Alan M. Brichta

Keyword(s):

Hair Cells ◽

Low Frequency ◽

Type I ◽

Type Ii Cells ◽

Type Ii ◽

Active Components ◽

Response Dynamics ◽

Steady Current ◽

Slow Type ◽

Sinusoidal Currents

Controlled currents were used to study possible functions of voltage-sensitive, outwardly rectifying conductances. Results were interpreted with linearized Hodgkin-Huxley theory. Because of their more hyperpolarized resting potentials and lower impedances, type I hair cells require larger currents to be depolarized to a given voltage than do type II hair cells. “Fast” type II cells, so-called because of the fast activation of their outward currents, show slightly underdamped responses to current steps with resonant (best) frequencies of 40–85 Hz, well above the bandwidth of natural head movements. Reflecting their slower activation kinetics, type I and “slow” type II cells have best frequencies of 15–30 Hz and are poorly tuned, being critically damped or overdamped. Linearized theory identified the factors responsible for tuning quality. Our fast type II hair cells show only modestly underdamped responses because their steady-state I-V curves are not particularly steep. The even poorer tuning of our type I and slow type II cells can be attributed to their slow activation kinetics and large conductances. To study how ionic currents shape response dynamics, we superimposed sinusoidal currents of 0.1–100 Hz on a small depolarizing steady current intended to simulate resting conditions in vivo. The steady current resulted in a slow inactivation, most pronounced in fast type II cells and least pronounced in type I cells. Because of inactivation, fast type II cells have nearly passive response dynamics with low-frequency gains of 500–1,000 MΩ. In contrast, type I and slow type II cells show active components in the vestibular bandwidth and low-frequency gains of 20–100 and 100–500 MΩ, respectively. As there are no differences in the responses to sinusoidal currents for fast type II cells from the torus and planum, voltage-sensitive currents are unlikely to be responsible for the large differences in gains and response dynamics of afferents innervating these two regions of the peripheral zone. The low impedances and active components of type I cells may be related to the low gains and modestly phasic response dynamics of calyx-bearing afferents.

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Morphological Changes in Rat Vestibular System Following Weightlessness

Journal of Vestibular Research ◽

10.3233/ves-1993-3305 ◽

1993 ◽

Vol 3 (3) ◽

pp. 241-251

Author(s):

Muriel D. Ross

Keyword(s):

Hair Cells ◽

Space Shuttle ◽

Morphological Changes ◽

Distributed Processing ◽

Type I ◽

Type Ii Cells ◽

Type Ii ◽

Ribbon Synapses ◽

Gravity Receptors ◽

I Cells

Mammalian gravity receptors (maculas) are morphologically organized for weighted, parallel distributed processing of information. There are two basic circuits: 1) highly channeled, type I cell to calyx; and 2) distributed modifying, type II cells to calyces and processes. The latter circuit should be the more adaptable since it modifies final output. To test this hypothesis, rats were flown in microgravity for 9 days aboard a space shuttle and euthanized shortly after landing. Hair cells and ribbon synapses from maculas of 3 flight and 3 ground control rats were studied ultrastructurally in blocks of 50 serial sections. Synapses increased by approximately 41% in type I cells and by approximately 55% in type II cells in flight animals. There was a shift toward the spherular form of ribbon synapse in both types of hair cells in flight animals (P ⩽ 0.0001), a near doubling of pairs in the flight rats (P ⩽ 0.0001), and an increase, by a factor of 12, in groups of synapses in type II cells (P ⩽ 0.0001). Current findings tend to support the stated hypothesis and indicate that mature utricular hair cells retain synaptic plasticity, permitting adaptation to an altered gravitational environment.

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Voltage-Gated Calcium Channel Currents in Type I and Type II Hair Cells Isolated From the Rat Crista

Journal of Neurophysiology ◽

10.1152/jn.00244.2003 ◽

2003 ◽

Vol 90 (1) ◽

pp. 155-164 ◽

Cited By ~ 51

Author(s):

Hong Bao ◽

Weng Hoe Wong ◽

Jay M. Goldberg ◽

Ruth Anne Eatock

Keyword(s):

Hair Cells ◽

Type I ◽

Type Ii Cells ◽

Type Ii ◽

Α Subunit ◽

Voltage Gated ◽

Type I Cells ◽

Channel Currents ◽

I Cells

When studied in vitro, type I hair cells in amniote vestibular organs have a large, negatively activating K+ conductance. In type II hair cells, as in nonvestibular hair cells, outwardly rectifying K+ conductances are smaller and more positively activating. As a result, type I cells have more negative resting potentials and smaller input resistances than do type II cells; large inward currents fail to depolarize type I cells above –60 mV. In nonvestibular hair cells, afferent transmission is mediated by voltage-gated Ca2+ channels that activate positive to –60 mV. We investigated whether Ca2+ channels in type I cells activate more negatively so that quantal transmission can occur near the reported resting potentials. We used the perforated patch method to record Ca2+ channel currents from type I and type II hair cells isolated from the rat anterior crista (postnatal days 4–20). The activation range of the Ca2+ currents of type I hair cells differed only slightly from that of type II cells or nonvestibular hair cells. In 5 mM external Ca2+, currents in type I and type II cells were half-maximal at –41.1 ± 0.5 (SE) mV ( n = 10) and –37.2 ± 0.2 mV ( n = 10), respectively. In physiological external Ca2+ (1.3 mM), currents in type I cells were half-maximal at –46 ± 1 mV ( n = 8) and just 1% of maximal at –72 mV. These results lend credence to suggestions that type I cells have more positive resting potentials in vivo, possibly through K+ accumulation in the synaptic cleft or inhibition of the large K+ conductance. Ca2+ channel kinetics were also unremarkable; in both type I and type II cells, the currents activated and deactivated rapidly and inactivated only slowly and modestly even at large depolarizations. The Ca2+ current included an L-type component with relatively low sensitivity to dihydropyridine antagonists, consistent with the α subunit being CaV1.3 (α1D). Rat vestibular epithelia and ganglia were probed for L-type α-subunit expression with the reverse transcription-polymerase chain reaction. The epithelia expressed CaV1.3 and the ganglia expressed CaV1.2 (α1C).

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