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

2002 ◽  
Vol 88 (6) ◽  
pp. 3279-3292 ◽  
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.

Morphological Changes in Rat Vestibular System Following Weightlessness

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.

Morphological Identification of Physiologically Characterized Afferents Innervating the Turtle Posterior Crista

2000 ◽  
Vol 83 (3) ◽  
pp. 1202-1223 ◽  
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.

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

2002 ◽  
Vol 88 (6) ◽  
pp. 3259-3278 ◽  
Author(s):  
Alan M. Brichta ◽  
Anne Aubert ◽  
Ruth Anne Eatock ◽  
Jay M. Goldberg
Keyword(s):  
Hair Cells ◽  
Central Zone ◽  
Peripheral Zone ◽  
Type I ◽  
Type Ii Cells ◽  
Type Ii ◽  
Fast Kinetics ◽  
Outward Currents ◽  
Inward Currents ◽  
Inwardly Rectifying

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.

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

2003 ◽  
Vol 90 (1) ◽  
pp. 155-164 ◽  
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).

scholarly journals CD95 death-inducing signaling complex formation and internalization occur in lipid rafts of type I and type II cells

2004 ◽  
Vol 34 (7) ◽  
pp. 1930-1940 ◽  
Author(s):  
Adriana Eramo ◽  
Massimo Sargiacomo ◽  
Lucia Ricci-Vitiani ◽  
Matilde Todaro ◽  
Giorgio Stassi ◽  
...  
Keyword(s):  
Complex Formation ◽  
Lipid Rafts ◽  
Type I ◽  
Type Ii Cells ◽  
Type Ii ◽  
Signaling Complex

The Roles Potassium Currents Play in Regulating the Electrical Activity of Ventral Cochlear Nucleus Neurons

2003 ◽  
Vol 89 (6) ◽  
pp. 3097-3113 ◽  
Author(s):  
Jason S. Rothman ◽  
Paul B. Manis
Keyword(s):  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Threshold Current ◽  
Repetitive Firing ◽  
Resting Membrane Potential ◽  
Type I ◽  
Type Ii Cells ◽  
Type Ii ◽  
Ventral Cochlear Nucleus ◽  
Discharge Patterns

Using kinetic data from three different K+ currents in acutely isolated neurons, a single electrical compartment representing the soma of a ventral cochlear nucleus (VCN) neuron was created. The K+ currents include a fast transient current ( IA), a slow-inactivating low-threshold current ( ILT), and a noninactivating high-threshold current ( IHT). The model also includes a fast-inactivating Na+ current, a hyperpolarization-activated cation current ( Ih), and 1–50 auditory nerve synapses. With this model, the role IA, ILT, and IHT play in shaping the discharge patterns of VCN cells is explored. Simulation results indicate that IHT mainly functions to repolarize the membrane during an action potential, and IA functions to modulate the rate of repetitive firing. ILT is found to be responsible for the phasic discharge pattern observed in Type II cells (bushy cells). However, by adjusting the strength of ILT, both phasic and regular discharge patterns are observed, demonstrating that a critical level of ILT is necessary to produce the Type II response. Simulated Type II cells have a significantly faster membrane time constant in comparison to Type I cells (stellate cells) and are therefore better suited to preserve temporal information in their auditory nerve inputs by acting as precise coincidence detectors and having a short refractory period. Finally, we demonstrate that modulation of Ih, which changes the resting membrane potential, is a more effective means of modulating the activation level of ILT than simply modulating ILT itself. This result may explain why ILT and Ih are often coexpressed throughout the nervous system.

Disparate cytokine regulation of ICAM-1 in rat alveolar epithelial cells and pulmonary endothelial cells in vitro

1995 ◽  
Vol 269 (1) ◽  
pp. L127-L135 ◽  
Author(s):  
W. W. Barton ◽  
S. Wilcoxen ◽  
P. J. Christensen ◽  
R. Paine
Keyword(s):  
Endothelial Cells ◽  
Epithelial Cells ◽  
Inflammatory Cytokines ◽  
Alveolar Epithelial Cells ◽  
Normal Lung ◽  
Type I ◽  
Type Ii Cells ◽  
Type Ii ◽  
Alveolar Epithelial

Intercellular adhesion molecule-1 (ICAM-1) is expressed at high levels on type I alveolar epithelial cells in the normal lung and is induced in vitro as type II cells spread in primary culture. In contrast, in most nonhematopoetic cells ICAM-1 expression is induced in response to inflammatory cytokines. We have formed the hypothesis that the signals that control ICAM-1 expression in alveolar epithelial cells are fundamentally different from those controlling expression in most other cells. To test this hypothesis, we have investigated the influence of inflammatory cytokines on ICAM-1 expression in isolated type II cells that have spread in culture and compared this response to that of rat pulmonary artery endothelial cells (RPAEC). ICAM-1 protein, determined both by a cell-based enzyme-linked immunosorbent assay and by Western blot analysis, and mRNA were minimally expressed in unstimulated RPAEC but were significantly induced in a time- and dose-dependent manner by treatment with tumor necrosis factor-alpha, interleukin-1 beta, or interferon-gamma. In contrast, these cytokines did not influence the constitutive high level ICAM-1 protein expression in alveolar epithelial cells and only minimally affected steady-state mRNA levels. ICAM-1 mRNA half-life, measured in the presence of actinomycin D, was relatively long at 7 h in alveolar epithelial cells and 4 h in RPAEC. The striking lack of response of ICAM-1 expression by alveolar epithelial cells to inflammatory cytokines is in contrast to virtually all other epithelial cells studied to date and supports the hypothesis that ICAM-1 expression by these cells is a function of cellular differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

A delayed rectifier conductance in type I hair cells of the mouse utricle

1996 ◽  
Vol 76 (2) ◽  
pp. 995-1004 ◽  
Author(s):  
A. Rusch ◽  
R. A. Eatock
Keyword(s):  
Hair Cells ◽  
Time Course ◽  
Dissociation Constants ◽  
Resting Potential ◽  
Delayed Rectifier ◽  
Type I ◽  
Type Ii ◽  
Voltage Range ◽  
Average Maximum

1. Membrane currents of hair cells in acutely excised or cultured mouse utricles were recorded with the whole cell voltage-clamp method at temperatures between 23 and 36 degrees C. 2. Type I and II hair cells both had delayed rectifier conductances that activated positive to -55 mV. 3. Type I, but not type II, hair cells had an additional delayed rectifier conductance (gK,L) with an activation range that was unusually negative and variable. At 23-25 degrees C, V(1/2) values ranged from -88 to -62 mV in 57 cells. 4. gK,L was very large. At 23-25 degrees C, the average maximum chord conductance was 75 +/- 65 nS (mean +/- SD, n = 57; measured at -54 mV), or approximately 21 nS/pF of cell capacitance. 5. gK,L was highly selective for K+ over Na+ (permeability ratio PNa+/PK+:0.006), but unlike other delayed rectifiers, gK,L was significantly permeable to Cs+ (PCs+/PK+:0.31). gK,L was independent of extracellular Ca2+. 6. At -64 mV, Ba2+ and 4-aminopyridine blocked gK,L with apparent dissociation constants of 2.0 mM and 43 microM, respectively. Extracellular Cs+ (5 mM) blocked gK,L by 50% at -124 mV. Apamin (100 nM) and dendrotoxin (10 nM) has no effect. 7. The kinetic data of gK,L are consistent with a sequential gating model with at least two closed states and one open state. The slow activation kinetics (principal time constants at 23-25 degrees C:600-200 ms) had a thermal Q10 of 2.1. Inactivation (Q10:2.7) was partial at all temperatures. Deactivation followed a double-exponential time course and had a Q10 of 2.0. 8. At 23-25 degrees C, gK,L was appreciably activated at the mean resting potential of type I hair cells (-77 +/- 3.1 mV, n = 62), so that input conductances were often more than an order of magnitude larger than those of type II cells. If these conditions hold in vivo, type I cells would produce unusually small receptor potentials. Warming the cells to 36 degrees C produced parallel shifts in gK,L's activation range (0.8 +/- 0.3 mV/degrees C, n = 8), and in the resting potential (0.6 +/- 0.3 mV/degrees C, n = 4). Thus the high input conductances were not an artifact of unphysiological temperatures but remained high near body temperature. It remains possible that in vivo gK,L's activation range is less negative and input conductances are lower; the large variance in the voltage range of activation suggests that it may be subject to modulation.

Sulfation of extracellular matrices modifies responses of alveolar type II cells to fibroblast growth factors

1996 ◽  
Vol 271 (5) ◽  
pp. L688-L697 ◽  
Author(s):  
P. L. Sannes ◽  
J. Khosla ◽  
P. W. Cheng
Keyword(s):  
Growth Factors ◽  
Biological Significance ◽  
Alveolar Type ◽  
Type I ◽  
Type Ii Cells ◽  
Type Ii ◽  
Fibroblast Growth ◽  
Alveolar Type Ii Cells ◽  
Proliferation And Differentiation ◽  
Type Ii Cell

The pulmonary alveolar basement membrane (BM) associated with alveolar type II cells has been shown to be significantly less sulfated than that of type I cells. To examine the biological significance of this observation, we measured the incorporation of 5-bromodeoxyuridine (BrdU) as an indicator of DNA synthesis in isolated rat type II cells cultured for 72-120 h on substrata that were naturally sulfated, not sulfated, or chemically desulfated in serum-free, hormonally defined media, with and without selected growth factors. The percentage of cells incorporating BrdU was significantly elevated by desulfated chondroitin sulfate in the presence of fibroblast growth factor-2 (FGF-2 or basic FGF) and depressed by heparin in the presence of either FGF-1 or acidic FGF or FGF-2. This depressive effect was lost by removing sulfate from the heparin. Some responses were dependent on the period of time in culture and concentration and molecular weight of the substrata. These observations support the notion that sulfation per se of certain components of BM is a key determinant of type II cell responses to select growth factors that may define patterns of proliferation and differentiation.

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