scholarly journals Calmodulin Contributes to Gating Control in Olfactory Calcium-activated Chloride Channels

2006 ◽  
Vol 127 (6) ◽  
pp. 737-748 ◽  
Author(s):  
Hiroshi Kaneko ◽  
Frank Möhrlen ◽  
Stephan Frings
Keyword(s):  
Sensory Neurons ◽  
Signal Amplification ◽  
Single Channel ◽  
Feedback Inhibition ◽  
Ion Selectivity ◽  
Sensory Information ◽  
Activation Mechanism ◽  
Ca Channels ◽  
Cl Channels ◽  
Ca Sensitivity

In sensory neurons of the peripheral nervous system, receptor potentials can be amplified by depolarizing Cl currents. In mammalian olfactory sensory neurons (OSNs), this anion-based signal amplification results from the sequential activation of two distinct types of transduction channels: cAMP-gated Ca channels and Ca-activated Cl channels. The Cl current increases the initial receptor current about 10-fold and leads to the excitation of the neuron. Here we examine the activation mechanism of the Ca-dependent Cl channel. We focus on calmodulin, which is known to mediate Ca effects on various ion channels. We show that the cell line Odora, which is derived from OSN precursor cells in the rat olfactory epithelium, expresses Ca-activated Cl channels. Single-channel conductance, ion selectivity, voltage dependence, sensitivity to niflumic acid, and Ca sensitivity match between Odora channels and OSN channels. Transfection of Odora cells with CaM mutants reduces the Ca sensitivity of the Cl channels. This result points to the participation of calmodulin in the gating process of Ca-ativated Cl channels, and helps to understand how signal amplification works in the olfactory sensory cilia. Calmodulin was previously shown to mediate feedback inhibition of cAMP-synthesis and of the cAMP-gated Ca channels in OSNs. Our results suggest that calmodulin may also be instrumental in the generation of the excitatory Cl current. It appears to play a pivotal role in the peripheral signal processing of olfactory sensory information. Moreover, recent results from other peripheral neurons, as well as from smooth muscle cells, indicate that the calmodulin-controlled, anion-based signal amplification operates in various cell types where it converts Ca signals into membrane depolarization.

scholarly journals Caffeine-induced inhibition of inositol(1,4,5)-trisphosphate-gated calcium channels from cerebellum.

1994 ◽  
Vol 5 (1) ◽  
pp. 97-103 ◽  
Author(s):  
I Bezprozvanny ◽  
S Bezprozvannaya ◽  
B E Ehrlich
Keyword(s):  
Lipid Bilayers ◽  
Inhibitory Action ◽  
Single Channel ◽  
Ryanodine Receptors ◽  
Single Channels ◽  
Ca Channels ◽  
Open Time ◽  
Inositol 1,4,5 Trisphosphate ◽  
Insp3 Receptors ◽  
Intracellular Ca

Effects of the xanthine drug caffeine on inositol (1,4,5)-trisphosphate (InsP3)-gated calcium (Ca) channels from canine cerebellum were studied using single channels incorporated into planar lipid bilayers. Caffeine, used widely as an agonist of ryanodine receptors, inhibited the activity of InsP3-gated Ca channels in a noncooperative fashion with half-inhibition at 1.64 mM caffeine. The frequency of channel openings was decreased more than threefold after addition of 5 mM caffeine; there was only a small effect on mean open time of the channels, and the single channel conductance was unchanged. Increased InsP3 concentration overcame the inhibitory action of caffeine, but caffeine did not reduce specific [3H]InsP3 binding to the receptor. The inhibitory action of caffeine on InsP3 receptors suggests that the action of caffeine on the intracellular Ca pool must be interpreted with caution when both ryanodine receptors and InsP3 receptors are present in the cell.

Stilbene disulfonate blockade of colonic secretory Cl- channels in planar lipid bilayers

1989 ◽  
Vol 256 (4) ◽  
pp. C902-C912 ◽  
Author(s):  
R. J. Bridges ◽  
R. T. Worrell ◽  
R. A. Frizzell ◽  
D. J. Benos
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Membrane Vesicles ◽  
Kinetic Scheme ◽  
Disulfonic Acid ◽  
Lipid Bilayer Membranes ◽  
Plasma Membrane Vesicles ◽  
Open Probability ◽  
Cl Channel ◽  
Cl Channels

We studied blockade by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS) of a secretory Cl- channel from colonic enterocyte plasma membrane vesicles incorporated into planar lipid bilayer membranes. Except for intermittent long-lived closed periods (100 ms to several min), the control channel open probability (Po) was greater than 90%. DNDS, added to the cis or vesicle-containing side, which corresponds to the outer membrane side of the channel, caused a dramatic increase in the number of current transitions from the open-to-closed state. DNDS caused a concentration-dependent decrease in Po with a maximum inhibition of 95 +/- 2.0% and a half-maximal inhibitory concentration of 3.3 +/- 1.4 microM. DNDS added to the trans side of the channel had no effect on either the single-channel conductance or kinetic behavior of the channel. Kinetic analysis revealed that DNDS blockade from the cis side could be explained by a linear, closed-open-blocked, kinetic scheme. The estimated DNDS block rate constants were kon = 3.2 X 10(7) M-1.s-1 and koff = 52 s-1, yielding an equilibrium dissociation constant (KD) of 2.1 +/- 0.38 microM, similar to the Ki for inhibition of Po. The effects of DNDS were fully reversible after perfusion of the cis compartment with DNDS-free solution. In contrast, the covalently reactive 4,4'-diisothiocyano-substituted stilbene disulfonate caused an irreversible blockade of the Cl- channel.

scholarly journals Widespread inhibition, antagonism, and synergy in mouse olfactory sensory neurons in vivo

2019 ◽  
Author(s):  
Shigenori Inagaki ◽  
Ryo Iwata ◽  
Masakazu Iwamoto ◽  
Takeshi Imai
Keyword(s):  
Sensory Neurons ◽  
Calcium Imaging ◽  
Odorant Receptor ◽  
Sensory Information ◽  
Olfactory Sensory Neurons ◽  
Axon Terminals ◽  
Two Photon ◽  
Odor Mixtures ◽  
The Brain

SUMMARYSensory information is selectively or non-selectively inhibited and enhanced in the brain, but it remains unclear whether this occurs commonly at the peripheral stage. Here, we performed two-photon calcium imaging of mouse olfactory sensory neurons (OSNs) in vivo and found that odors produce not only excitatory but also inhibitory responses at their axon terminals. The inhibitory responses remained in mutant mice, in which all possible sources of presynaptic lateral inhibition were eliminated. Direct imaging of the olfactory epithelium revealed widespread inhibitory responses at OSN somata. The inhibition was in part due to inverse agonism toward the odorant receptor. We also found that responses to odor mixtures are often suppressed or enhanced in OSNs: Antagonism was dominant at higher odor concentrations, whereas synergy was more prominent at lower odor concentrations. Thus, odor responses are extensively tuned by inhibition, antagonism, and synergy, at the early peripheral stage, contributing to robust odor representations.

scholarly journals Dynamic Interaction of Norfloxacin to Magnesium Monitored by Bacterial Outer Membrane Nanopores

2020 ◽  
Author(s):  
Jiajun Wang ◽  
Jigneshkumar Dahyabhai Prajapati ◽  
Ulrich Kleinekathöfer ◽  
Mathias Winterhalter
Keyword(s):  
Outer Membrane ◽  
Lipid Bilayers ◽  
Brownian Dynamics ◽  
Single Channel ◽  
Ion Selectivity ◽  
Computational Modelling ◽  
Free Energy Calculations ◽  
Divalent Ions ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations

The effect of divalent ions on the permeability of norfloxacin across the major outer membrane channels from <i>E. coli</i> (OmpF, OmpC) and <i>E. aerogenes</i> (Omp35, Omp36) has been investigated at the single channel level. To understand the rate limiting steps in permeation, we reconstituted single porin into planar lipid bilayers and analyzed the ion current fluctuations caused in the presence of norfloxacin. To obtain an atomistic view, we complemented the experiments with millisecond-long free energy calculations based on temperature-accelerated Brownian dynamics simulations to identify the most probable permeation pathways of the antibiotics through the respective pore. Both, experimental analysis and computational modelling, suggest that norfloxacin is able to permeate through the larger porins, i.e., OmpF, OmpC, and Omp35, whereas it only binds to the slightly narrower porin Omp36. Moreover, divalent ions can bind to negatively charged residues inside the porin, reversing the ion selectivity of the pore. In addition, the divalent ions can chelate with the fluoroquinolones and alter their physicochemical properties. The results suggest that the conjugation must break with either one of them when the antibiotics molecules bypass the lumen of the porin, with the conjugation to the antibiotic being more stable than that to the pore. In general, the permeation or binding process of fluoroquinolone in porins occurs irrespective of the presence of divalent ions, but the presences of divalent ions can vary the kinetics significantly.

Cranial Nerves I and II

2021 ◽  
pp. 115-119
Author(s):  
Kelly D. Flemming ◽  
Eduardo E. Benarroch
Keyword(s):  
Optic Nerve ◽  
Sensory Neurons ◽  
Chloride Channels ◽  
Calcium Influx ◽  
Cranial Nerves ◽  
Sensory Information ◽  
Olfactory Receptors ◽  
Olfactory Nerve ◽  
Afferent Nerve ◽  
Gated Channel

Cranial nerves I (olfactory nerve) and II (optic nerve) are supratentorial, paired cranial nerves. This chapter provides an overview of their anatomy. Cranial nerve I is a special visceral afferent nerve carrying sensory information about odors. Olfactory receptors lie in the nasal cavity. Odorants activate receptors within the cilia of olfactory sensory neurons and trigger the opening of a cyclic nucleotide–gated channel. This channel allows a calcium influx and the opening of calcium-activated chloride channels. Depolarization then occurs.

Nonselective cation and Cl channels in luminal membrane of the marginal cell

1993 ◽  
Vol 265 (1) ◽  
pp. C72-C78 ◽  
Author(s):  
H. Sunose ◽  
K. Ikeda ◽  
Y. Saito ◽  
A. Nishiyama ◽  
T. Takasaka
Keyword(s):  
Single Channel ◽  
Patch Clamp Technique ◽  
Cl Channel ◽  
Luminal Membrane ◽  
Cl Channels ◽  
Cytoplasmic Acidification ◽  
Marginal Cells ◽  
Single Channel Currents ◽  
Channel Currents ◽  
Linear Conductance

Single-channel currents of the luminal membrane of marginal cells dissected from the guinea pig cochlea were investigated using the patch-clamp technique. Nonselective cation channels having a linear conductance of 27 pS were activated by depolarization, cytoplasmic Ca2+, and cytoplasmic acidification. Cytoplasmic ATP inactivated the channel. A mixture of 3-isobutyl-1-methylxanthine and forskolin activated a small-conductance Cl channel in the cell-attached mode. On excision in the inside-out mode, the Cl channel was inactivated, but it was reactivated by a cytoplasmic catalytic subunit of protein kinase A with ATP. This Cl channel had a linear conductance of 12 pS, and its activity was little affected by voltage. The sequence of permeation by anions was Br- > Cl > I-. The Cl channel blocker diphenylamine-2-carboxylic acid (3 mM) completely blocked the channel, but 5-nitro-2-(3-phenylpropylamino)-benzoic acid (50 microM) blocked it only partially. The above-mentioned characteristics are similar to those of the well-demonstrated Cl- channel, cystic fibrosis transmembrane regulator.

Sensitization of the gill and siphon withdrawal reflex of Aplysia: multiple sites of change in the neuronal network

1993 ◽  
Vol 70 (3) ◽  
pp. 1210-1220 ◽  
Author(s):  
L. E. Trudeau ◽  
V. F. Castellucci
Keyword(s):  
Sensory Neuron ◽  
Sensory Neurons ◽  
Motor Neurons ◽  
Neuronal Network ◽  
Feedback Inhibition ◽  
Excitatory Input ◽  
Major Mechanism ◽  
Withdrawal Reflex ◽  
The Difference ◽  
Central Synapses

1. Recent studies have emphasized the major contribution of interneuronal transmission to the mediation and learning-associated modulation of the gill and siphon withdrawal (GSW) reflex of Aplysia. We wish to provide more direct support for the hypothesis that inhibitory junctions are crucial sites of plasticity. 2. In parallel experiments we investigated modulation at five major sites of synaptic transmission in the GSW network: 1) from sensory neurons to motor neurons, 2) from sensory neurons to excitatory interneurons (INTs+) 3) from INTs+ to motor neurons (MNs), 4) from inhibitory interneurons (INTs-) to INTs+, and 5) from INTs+ to INTs-. 3. While recording simultaneously from a single sensory neuron of the LE cluster, an INT+, and a MN, we found that both LE-MN and LE-INTs+ synapses were facilitated by the activation of modulator neurons by stimulation of the left pleuroabdominal connective (185 and 93%, respectively) as well as by serotonin (5-HT) (191 and 84%). Junctions of the second type were therefore less facilitated. The difference in the magnitude of facilitation at these two sites is an indication of a branch-specific, differential efficacy in the modulation of different central synapses made by a single neuron. 4. Although INT(+)-MN junctions have the capacity to display marked posttetanic potentiation, they are not significantly potentiated after connective stimulation. Sensitization of the GSW reflex is therefore not necessarily accompanied by a modification of transmission at these synapses. 5. Inhibitory transmission to INTs+ is significantly reduced by connective stimulation (36%) and by 5-HT (71%). This supports the hypothesis that a reduction of feedback inhibition into INTs+ is a major mechanism of reflex sensitization and may account for the increased evoked firing of INTs+ that is observed after connective stimulation. 6. The excitatory input to INTs- is selectively decreased by 5-HT (50%) and by the molluscan neuropeptide small cardioactive peptide B (38%). This latter effect, which could produce disinhibition of INTs+, may explain the previous observation that this peptide is able to potentiate the evoked input to MNs of the reflex at a concentration (1 microM) that fails to modify monosynaptic sensory-motor transmission. 7. These results indicate that transmission through a small neuronal network that mediates a withdrawal reflex in Aplysia may be modulated at multiple sites and by different mechanisms. These mechanisms include: 1) branch-specific facilitation of sensory neuron outputs and 2) inhibition of INT(-)-INT+ inhibitory postsynaptic potentials by endogenous modulatory neurons and by 5-HT.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced single-channel K+ current in arterial membranes from genetically hypertensive rats

1993 ◽  
Vol 264 (5) ◽  
pp. H1337-H1345 ◽  
Author(s):  
S. K. England ◽  
T. A. Wooldridge ◽  
W. J. Stekiel ◽  
N. J. Rusch
Keyword(s):  
Single Channel ◽  
Muscle Cells ◽  
Ca Channel ◽  
Ca Channels ◽  
Hypertensive Rats ◽  
Genetically Hypertensive Rats ◽  
K Current ◽  
Inside Out ◽  
Genetically Hypertensive ◽  
Arterial Muscle

Arterial smooth muscle from hypertensive rats shows an increased membrane permeability to K+ that depends on Ca2+ influx. To define the mechanism of this membrane alteration, we tested the hypothesis that Ca(2+)-dependent K+ current (IK(Ca)) is increased in arterial muscle membranes from genetically hypertensive rats. Single-channel K+ currents measured in cell-attached and inside-out aortic membrane patches from spontaneously hypertensive rats (SHR) were compared with those from normotensive Wistar-Kyoto rats (WKY). Inside-out patches from both rat strains showed a predominant 225 pS, Ca(2+)- and voltage-dependent K+ channel in symmetrical 145 mM KCl solutions, which was blocked by tetraethylammonium [concentration for half-maximal block (IC50) < or = 0.3 mM]. In cell-attached patches of aortic muscle cells bathed in physiological salt solution, this channel [IK(Ca) channel] showed a fivefold higher open-state probability (NPo) in SHR as compared with WKY. This increased NPo of SHR IK(Ca) channels in membranes of intact aortic muscle cells was not correlated with an altered membrane potential in current-clamped SHR myocytes or with changes in cytosolic free Ca2+ concentration in fura-2-loaded aortic muscle cells. However, inside-out aortic membrane patches from SHR showed more detected IK(Ca) channels per patch, a higher IK(Ca) channel NPo, and a greater total patch current than their WKY counterparts. Further analysis revealed a greater Ca2+ sensitivity of SHR than WKY IK(Ca) channels. These results suggest that IK(Ca) channel function is altered in isolated membrane patches of arterial muscle from genetically hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2

2012 ◽  
Vol 140 (1) ◽  
pp. 41-53 ◽  
Author(s):  
Vsevolod Telezhkin ◽  
David A. Brown ◽  
Alasdair J. Gibb
Keyword(s):  
Potassium Channels ◽  
Single Channel ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Water Soluble ◽  
Activation Mechanism ◽  
Quantitative Relation ◽  
Open Probability ◽  
Activation Curve ◽  
M Channels

Low-threshold voltage-gated M-type potassium channels (M channels) are tetraheteromers, commonly of two Kv7.2 and two Kv7.3 subunits. Though gated by voltage, the channels have an absolute requirement for binding of the membrane phospholipid phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) to open. We have investigated the quantitative relation between the concentration of a water-soluble PI(4,5)P2 analog, dioctanoyl-PI(4,5)P2 (DiC8-PI(4,5)P2), and channel open probability (Popen) by fast application of increasing concentrations of DiC8-PI(4,5)P2 to the inside face of membrane patches excised from Chinese hamster ovary cells expressing M channels as heteromeric Kv7.2/7.3 subunits. The rationale for the experiments is that this will mimic the effect of changes in membrane PI(4,5)P2 concentration. Single-channel conductances from channel current–voltage relations in cell-attached mode were 9.2 ± 0.1 pS with a 2.5-mM pipette [K+]. Plots of Popen against DiC8-PI(4,5)P2 concentration were best fitted using a two-component concentration–Popen relationship with high and low affinity, half-maximal effective concentration (EC50) values of 1.3 ± 0.14 and 75.5 ± 2.5 µM, respectively, and Hill slopes of 1.4 ± 0.06. In contrast, homomeric channels from cells expressing only Kv7.2 or Kv7.3 constructs yielded single-component curves with EC50 values of 76.2 ± 19.9 or 3.6 ± 1.0 µM, respectively. When wild-type (WT) Kv7.2 was coexpressed with a mutated Kv7.3 subunit with &gt;100-fold reduced sensitivity to PI(4,5)P2, the high-affinity component of the activation curve was lost. Fitting the data for WT and mutant channels to an activation mechanism with independent PI(4,5)P2 binding to two Kv7.2 and two Kv7.3 subunits suggests that the two components of the M-channel activation curve correspond to the interaction of PI(4,5)P2 with the Kv7.3 and Kv7.2 subunits, respectively, that channels can open when only the two Kv7.3 subunits have bound DiC8-PI(4,5)P2, and that maximum channel opening requires binding to all four subunits.

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