scholarly journals Interaction of a dinoflagellate neurotoxin with voltage-activated ion channels in a marine diatom

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4533 ◽  
Author(s):  
Sheila A. Kitchen ◽  
Andrea J. Bourdelais ◽  
Alison R. Taylor
Keyword(s):  
Action Potential ◽  
Binding Site ◽  
Action Potentials ◽  
Harmful Algal Bloom ◽  
Single Domain ◽  
Marine Phytoplankton ◽  
Marine Diatom ◽  
Membrane Excitability ◽  
Voltage Gated ◽  
Kinetics Of

Background The potent neurotoxins produced by the harmful algal bloom species Karenia brevis are activators of sodium voltage-gated channels (VGC) in animals, resulting in altered channel kinetics and membrane hyperexcitability. Recent biophysical and genomic evidence supports widespread presence of homologous sodium (Na+) and calcium (Ca2+) permeable VGCs in unicellular algae, including marine phytoplankton. We therefore hypothesized that VGCs of these phytoplankton may be an allelopathic target for waterborne neurotoxins produced by K. brevis blooms that could lead to ion channel dysfunction and disruption of signaling in a similar manner to animal Na+ VGCs. Methods We examined the interaction of brevetoxin-3 (PbTx-3), a K. brevis neurotoxin, with the Na+/Ca2+ VGC of the non-toxic diatom Odontella sinensis using electrophysiology. Single electrode current- and voltage- clamp recordings from O. sinensis in the presence of PbTx-3 were used to examine the toxin’s effect on voltage gated Na+/Ca2+ currents. In silico analysis was used to identify the putative PbTx binding site in the diatoms. We identified Na+/Ca2+ VCG homologs from the transcriptomes and genomes of 12 diatoms, including three transcripts from O. sinensis and aligned them with site-5 of Na+ VGCs, previously identified as the PbTx binding site in animals. Results Up to 1 µM PbTx had no effect on diatom resting membrane potential or membrane excitability. The kinetics of fast inward Na+/Ca2+ currents that underlie diatom action potentials were also unaffected. However, the peak inward current was inhibited by 33%, delayed outward current was inhibited by 25%, and reversal potential of the currents shifted positive, indicating a change in permeability of the underlying channels. Sequence analysis showed a lack of conservation of the PbTx binding site in diatom VGC homologs, many of which share molecular features more similar to single-domain bacterial Na+/Ca2+ VGCs than the 4-domain eukaryote channels. Discussion Although membrane excitability and the kinetics of action potential currents were unaffected, the permeation of the channels underlying the diatom action potential was significantly altered in the presence of PbTx-3. However, at environmentally relevant concentrations the effects of PbTx- on diatom voltage activated currents and interference of cell signaling through this pathway may be limited. The relative insensitivity of phytoplankton VGCs may be due to divergence of site-5 (the putative PbTx binding site), and in some cases, such as O. sinensis, resistance to toxin effects may be because of evolutionary loss of the 4-domain eukaryote channel, while retaining a single domain bacterial-like VGC that can substitute in the generation of fast action potentials.

Inhibition of Dendritic Calcium Influx by Activation of G-Protein–Coupled Receptors in the Hippocampus

1997 ◽  
Vol 78 (6) ◽  
pp. 3484-3488 ◽  
Author(s):  
Huanmian Chen ◽  
Nevin A. Lambert
Keyword(s):  
Calcium Channels ◽  
Action Potential ◽  
G Protein ◽  
Pyramidal Neuron ◽  
Action Potentials ◽  
Calcium Influx ◽  
G Protein Coupled Receptors ◽  
Voltage Gated ◽  
Voltage Gated Calcium Channels ◽  
G Protein Coupled

Chen, Huanmian and Nevin A. Lambert. Inhibition of dendritic calcium influx by activation of G-protein–coupled receptors in the hippocampus. J. Neurophysiol. 78: 3484–3488, 1997. Gi proteins inhibit voltage-gated calcium channels and activate inwardly rectifying K+ channels in hippocampal pyramidal neurons. The effect of activation of G-protein–coupled receptors on action potential-evoked calcium influx was examined in pyramidal neuron dendrites with optical and extracellular voltage recording. We tested the hypotheses that 1) activation of these receptors would inhibit calcium channels in dendrites; 2) hyperpolarization resulting from K+ channel activation would deinactivate low-threshold, T-type calcium channels on dendrites, increasing calcium influx mediated by these channels; and 3) activation of these receptors would inhibit propagation of action potentials into dendrites, and thus indirectly decrease calcium influx. Activation of adenosine receptors, which couple to Gi proteins, inhibited calcium influx in cell bodies and proximal dendrites without inhibiting action-potential propagation into the proximal dendrites. Inhibition of dendritic calcium influx was not changed in the presence of 50 μM nickel, which preferentially blocks T-type channels, suggesting influx through these channels is not increased by activation of G-proteins. Adenosine inhibited propagation of action potentials into the distal branches of pyramidal neuron dendrites, leading to a three- to fourfold greater inhibition of calcium influx in the distal dendrites than in the soma or proximal dendrites. These results suggest that voltage-gated calcium channels are inhibited in pyramidal neuron dendrites, as they are in cell bodies and terminals and thatG-protein–mediated inhibition of action-potential propagation can contribute substantially to inhibition of dendritic calcium influx.

scholarly journals Ca2+-Dependent, Stimulus-Specific Modulation of the Plasma Membrane Ca2+ Pump in Hippocampal Neurons

2009 ◽  
Vol 101 (5) ◽  
pp. 2563-2571 ◽  
Author(s):  
Michael J. Ferragamo ◽  
Jessica L. Reinardy ◽  
Stanley A. Thayer
Keyword(s):  
Plasma Membrane ◽  
Neuronal Activity ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Cyclopiazonic Acid ◽  
Synaptic Activity ◽  
Voltage Gated ◽  
Clearance Kinetics ◽  
Transient Elevation ◽  
Kinetics Of

The plasma membrane Ca2+ ATPase (PMCA) plays a major role in restoring Ca2+ to basal levels following transient elevation by neuronal activity. Here we examined the effects of various stimuli that increase [Ca2+]i on PMCA-mediated Ca2+ clearance from hippocampal neurons. We used indo-1-based microfluorimetry in the presence of cyclopiazonic acid to study the rate of PMCA-mediated recovery of Ca2+ elevated by a brief train of action potentials. [Ca2+]i recovery was described by an exponential decay and the time constant provided an index of PMCA-mediated Ca2+ clearance. PMCA function was assessed before and for ≥60 min following a 10-min priming stimulus of either 100 μM N-methyl-d-aspartate (NMDA), 0.1 mM Mg2+ (reduced extracellular Mg2+ induces intense excitatory synaptic activity), 30 mM K+, or control buffer. Recovery kinetics slowed progressively following priming with NMDA or 0.1 mM Mg2+; in contrast, Ca2+ clearance initially accelerated and then slowly returned to initial rates following priming with 30 mM K+-induced depolarization. Treatment with 10 μM calpeptin, an inhibitor of the Ca2+ activated protease calpain, prevented the slowing of kinetics observed following treatment with NMDA but had no affect on the recovery kinetics of control cells. Calpeptin also blocked the rapid acceleration of Ca2+ clearance following depolarization. In calpeptin-treated cells, 0.1 mM Mg2+ induced a graded acceleration of Ca2+ clearance. Thus in spite of producing comparable increases in [Ca2+]i, activation of NMDA receptors, depolarization-induced activation of voltage-gated Ca2+ channels and excitatory synaptic activity each uniquely affected Ca2+ clearance kinetics mediated by the PMCA.

KATP channels depress force by reducing action potential amplitude in mouse EDL and soleus muscle

2003 ◽  
Vol 285 (6) ◽  
pp. C1464-C1474 ◽  
Author(s):  
B. Gong ◽  
D. Legault ◽  
T. Miki ◽  
S. Seino ◽  
J. M. Renaud
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Metabolic Stress ◽  
Katp Channels ◽  
Channel Blockers ◽  
Action Potential Amplitude ◽  
Membrane Excitability ◽  
M Wave ◽  
Single Action ◽  
Potential Amplitude

Although ATP-sensitive K+ (KATP) channel openers depress force, channel blockers have no effect. Furthermore, the effects of channel openers on single action potentials are quite small. These facts raise questions as to whether 1) channel openers reduce force via an activation of KATP channels or via some nonspecific effects and 2) the reduction in force by KATP channels operates by changes in amplitude and duration of the action potential. To answer the first question we tested the hypothesis that pinacidil, a channel opener, does not affect force during fatigue in muscles of Kir6.2-/- mice that have no cell membrane KATP channel activity. When wild-type extensor digitorum longus (EDL) and soleus muscles were stimulated to fatigue with one tetanus per second, pinacidil increased the rate at which force decreased, prevented a rise in resting tension, and improved force recovery. Pinacidil had none of these effects in Kir6.2-/- muscles. To answer the second question, we tested the hypothesis that the effects of KATP channels on membrane excitability are greater during action potential trains than on single action potentials, especially during metabolic stress such as fatigue. During fatigue, M wave areas of control soleus remained constant for 90 s, suggesting no change in action potential amplitude for half of the fatigue period. In the presence of pinacidil, the decrease in M wave areas became significant within 30 s, during which time the rate of fatigue also became significantly faster compared with control muscles. It is therefore concluded that, once activated, KATP channels depress force and that this depression involves a reduction in action potential amplitude.

scholarly journals On the use of antibiotics for isolating bacteria-free cultures of marine phytoplankton organisms

1952 ◽  
Vol 31 (1) ◽  
pp. 97-106 ◽  
Author(s):  
C. P. Spencer
Keyword(s):  
Fresh Water ◽  
Solid Medium ◽  
Classical Method ◽  
Single Cells ◽  
Marine Phytoplankton ◽  
Marine Diatom ◽  
Sterile Medium ◽  
Kinetics Of ◽  
Water Species ◽  
Algal Cultures

In the course of some studies on the kinetics of growth and the biochemical activities of a marine diatom it became desirable to obtain bacteria-free cultures. The classical method of obtaining such pure algal cultures involves either repeatedly washing single cells in sterile medium or obtaining discrete bacteria-free algal colonies by growth on a solid medium. Both these methods have been widely applied to fresh-water species by Pringsheim (1946) and others, whilst Chu (1946) has used both methods with the marine diatom Nitzschia closterium (Ehrenberg) Wm. Smith forma minutissima.

scholarly journals Dendritic Voltage-Gated Ion Channels Regulate the Action Potential Firing Mode of Hippocampal CA1 Pyramidal Neurons

1999 ◽  
Vol 82 (4) ◽  
pp. 1895-1901 ◽  
Author(s):  
Jeffrey C. Magee ◽  
Michael Carruth
Keyword(s):  
Ion Channels ◽  
Action Potential ◽  
Large Amplitude ◽  
Action Potentials ◽  
Pyramidal Neurons ◽  
Burst Firing ◽  
Voltage Gated ◽  
Ca1 Pyramidal Neurons ◽  
Firing Mode ◽  
Voltage Gated Ion Channels

The role of dendritic voltage-gated ion channels in the generation of action potential bursting was investigated using whole cell patch-clamp recordings from the soma and dendrites of CA1 pyramidal neurons located in hippocampal slices of adult rats. Under control conditions somatic current injections evoked single action potentials that were associated with an afterhyperpolarization (AHP). After localized application of 4-aminopyridine (4-AP) to the distal apical dendritic arborization, the same current injections resulted in the generation of an afterdepolarization (ADP) and multiple action potentials. This burst firing was not observed after localized application of 4-AP to the soma/proximal dendrites. The dendritic 4-AP application allowed large-amplitude Na+-dependent action potentials, which were prolonged in duration, to backpropagate into the distal apical dendrites. No change in action potential backpropagation was seen with proximal 4-AP application. Both the ADP and action potential bursting could be inhibited by the bath application of nonspecific concentrations of divalent Ca2+ channel blockers (NiCl and CdCl). Ca2+ channel blockade also reduced the dendritic action potential duration without significantly affecting spike amplitude. Low concentrations of TTX (10–50 nM) also reduced the ability of the CA1 neurons to fire in the busting mode. This effect was found to be the result of an inhibition of backpropagating dendritic action potentials and could be overcome through the coordinated injection of transient, large-amplitude depolarizing current into the dendrite. Dendritic current injections were able to restore the burst firing mode (represented as a large ADP) even in the presence of high concentrations of TTX (300–500 μM). These data suggest the role of dendritic Na+ channels in bursting is to allow somatic/axonal action potentials to backpropagate into the dendrites where they then activate dendritic Ca2+ channels. Although it appears that most Ca2+ channel subtypes are important in burst generation, blockade of T- and R-type Ca2+ channels by NiCl (75 μM) inhibited action potential bursting to a greater extent than L-channel (10 μM nimodipine) or N-, P/Q-type (1 μM ω-conotoxin MVIIC) Ca2+ channel blockade. This suggest that the Ni-sensitive voltage-gated Ca2+ channels have the most important role in action potential burst generation. In summary, these data suggest that the activation of dendritic voltage-gated Ca2+ channels, by large-amplitude backpropagating spikes, provides a prolonged inward current that is capable of generating an ADP and burst of multiple action potentials in the soma of CA1 pyramidal neurons. Dendritic voltage-gated ion channels profoundly regulate the processing and storage of incoming information in CA1 pyramidal neurons by modulating the action potential firing mode from single spiking to burst firing.

scholarly journals Small-conductance Ca2+-activated K+ channels modulate action potential-induced Ca2+ transients in hippocampal neurons

2013 ◽  
Vol 109 (6) ◽  
pp. 1514-1524 ◽  
Author(s):  
Raffaella Tonini ◽  
Teresa Ferraro ◽  
Marisol Sampedro-Castañeda ◽  
Anna Cavaccini ◽  
Martin Stocker ◽  
...  
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Pyramidal Neurons ◽  
Apical Dendrite ◽  
Channel Blockers ◽  
Sk Channels ◽  
Hippocampal Pyramidal Neurons ◽  
Voltage Gated ◽  
Small Conductance

In hippocampal pyramidal neurons, voltage-gated Ca2+ channels open in response to action potentials. This results in elevations in the intracellular concentration of Ca2+ that are maximal in the proximal apical dendrites and decrease rapidly with distance from the soma. The control of these action potential-evoked Ca2+ elevations is critical for the regulation of hippocampal neuronal activity. As part of Ca2+ signaling microdomains, small-conductance Ca2+-activated K+ (SK) channels have been shown to modulate the amplitude and duration of intracellular Ca2+ signals by feedback regulation of synaptically activated Ca2+ sources in small distal dendrites and dendritic spines, thus affecting synaptic plasticity in the hippocampus. In this study, we investigated the effect of the activation of SK channels on Ca2+ transients specifically induced by action potentials in the proximal processes of hippocampal pyramidal neurons. Our results, obtained by using selective SK channel blockers and enhancers, show that SK channels act in a feedback loop, in which their activation by Ca2+ entering mainly through L-type voltage-gated Ca2+ channels leads to a reduction in the subsequent dendritic influx of Ca2+. This underscores a new role of SK channels in the proximal apical dendrite of hippocampal pyramidal neurons.

scholarly journals Recording action potential propagation in single axons using multi-electrode arrays

2017 ◽  
Author(s):  
Kenneth R. Tovar ◽  
Daniel C. Bridges ◽  
Bian Wu ◽  
Connor Randall ◽  
Morgane Audouard ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Action Potential ◽  
Sodium Channels ◽  
Action Potentials ◽  
Extracellular Recording ◽  
Electrode Arrays ◽  
Action Potential Propagation ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Axonal Arbors

AbstractThe small caliber of central nervous system (CNS) axons makes routine study of axonal physiology relatively difficult. However, while recording extracellular action potentials from neurons cultured on planer multi-electrode arrays (MEAs) we found activity among groups of electrodes consistent with action potential propagation in single neurons. Action potential propagation was evident as widespread, repetitive cooccurrence of extracellular action potentials (eAPs) among groups of electrodes. These eAPs occurred with invariant sequences and inter-electrode latencies that were consistent with reported measures of action potential propagation in unmyelinated axons. Within co-active electrode groups, the inter-electrode eAP latencies were temperature sensitive, as expected for action potential propagation. Our data are consistent with these signals primarily reflecting axonal action potential propagation, from axons with a high density of voltage-gated sodium channels. Repeated codetection of eAPs by multiple electrodes confirmed these eAPs are from individual neurons and averaging these eAPs revealed sub-threshold events at other electrodes. The sequence of electrodes at which eAPs co-occur uniquely identifies these neurons, allowing us to monitor spiking of single identified neurons within neuronal ensembles. We recorded dynamic changes in single axon physiology such as simultaneous increases and decreases in excitability in different portions of single axonal arbors over several hours. Over several weeks, we measured changes in inter-electrode propagation latencies and ongoing changes in excitability in different regions of single axonal arbors. We recorded action potential propagation signals in human induced pluripotent stem cell-derived neurons which could thus be used to study axonal physiology in human disease models.Significance StatementStudying the physiology of central nervous system axons is limited by the technical challenges of recording from axons with pairs of patch or extracellular electrodes at two places along single axons. We studied action potential propagation in single axonal arbors with extracellular recording with multi-electrode arrays. These recordings were non-invasive and were done from several sites of small caliber axons and branches. Unlike conventional extracellular recording, we unambiguously identified and labelled the neuronal source of propagating action potentials. We manipulated and quantified action potential propagation and found a surprisingly high density of axonal voltage-gated sodium channels. Our experiments also demonstrate that the excitability of different portions of axonal arbors can be independently regulated on time scales from hours to weeks.

scholarly journals Action potentials in Xenopus oocytes triggered by blue light

2020 ◽  
Vol 152 (5) ◽  
Author(s):  
Florian Walther ◽  
Dominic Feind ◽  
Christian vom Dahl ◽  
Christoph Emanuel Müller ◽  
Taulant Kukaj ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Blue Light ◽  
Action Potentials ◽  
Xenopus Oocytes ◽  
Na Channel ◽  
Xenopus Laevis Oocytes ◽  
Na Channels ◽  
Excitable Cells ◽  
Voltage Gated

Voltage-gated sodium (Na+) channels are responsible for the fast upstroke of the action potential of excitable cells. The different α subunits of Na+ channels respond to brief membrane depolarizations above a threshold level by undergoing conformational changes that result in the opening of the pore and a subsequent inward flux of Na+. Physiologically, these initial membrane depolarizations are caused by other ion channels that are activated by a variety of stimuli such as mechanical stretch, temperature changes, and various ligands. In the present study, we developed an optogenetic approach to activate Na+ channels and elicit action potentials in Xenopus laevis oocytes. All recordings were performed by the two-microelectrode technique. We first coupled channelrhodopsin-2 (ChR2), a light-sensitive ion channel of the green alga Chlamydomonas reinhardtii, to the auxiliary β1 subunit of voltage-gated Na+ channels. The resulting fusion construct, β1-ChR2, retained the ability to modulate Na+ channel kinetics and generate photosensitive inward currents. Stimulation of Xenopus oocytes coexpressing the skeletal muscle Na+ channel Nav1.4 and β1-ChR2 with 25-ms lasting blue-light pulses resulted in rapid alterations of the membrane potential strongly resembling typical action potentials of excitable cells. Blocking Nav1.4 with tetrodotoxin prevented the fast upstroke and the reversal of the membrane potential. Coexpression of the voltage-gated K+ channel Kv2.1 facilitated action potential repolarization considerably. Light-induced action potentials were also obtained by coexpressing β1-ChR2 with either the neuronal Na+ channel Nav1.2 or the cardiac-specific isoform Nav1.5. Potential applications of this novel optogenetic tool are discussed.

scholarly journals Quantitative Assessment of the Distributions of Membrane Conductances Involved in Action Potential Backpropagation Along Basal Dendrites

2009 ◽  
Vol 101 (3) ◽  
pp. 1524-1541 ◽  
Author(s):  
Corey D. Acker ◽  
Srdjan D. Antic
Keyword(s):  
Cortical Neurons ◽  
Action Potentials ◽  
Synaptic Integration ◽  
Membrane Properties ◽  
Delayed Rectifier ◽  
Published Data ◽  
Membrane Excitability ◽  
Voltage Gated ◽  
Prefrontal Cortical ◽  
Basal Dendrites

Basal dendrites of prefrontal cortical neurons receive strong synaptic drive from recurrent excitatory synaptic inputs. Synaptic integration within basal dendrites is therefore likely to play an important role in cortical information processing. Both synaptic integration and synaptic plasticity depend crucially on dendritic membrane excitability and the backpropagation of action potentials. We carried out multisite voltage-sensitive dye imaging of membrane potential transients from thin basal branches of prefrontal cortical pyramidal neurons before and after application of channel blockers. We found that backpropagating action potentials (bAPs) are predominantly controlled by voltage-gated sodium and A-type potassium channels. In contrast, pharmacologically blocking the delayed rectifier potassium, voltage-gated calcium, or Ih conductance had little effect on dendritic AP propagation. Optically recorded bAP waveforms were quantified and multicompartmental modeling was used to link the observed behavior with the underlying biophysical properties. The best-fit model included a nonuniform sodium channel distribution with decreasing conductance with distance from the soma, together with a nonuniform (increasing) A-type potassium conductance. AP amplitudes decline with distance in this model, but to a lesser extent than previously thought. We used this model to explore the mechanisms underlying two sets of published data involving high-frequency trains of APs and the local generation of sodium spikelets. We also explored the conditions under which IA down-regulation would produce branch strength potentiation in the proposed model. Finally, we discuss the hypothesis that a fraction of basal branches may have different membrane properties compared with sister branches in the same dendritic tree.

scholarly journals PROLONGED ACTION POTENTIALS FROM SINGLE NODES OF RANVIER

1958 ◽  
Vol 42 (1) ◽  
pp. 137-162 ◽  
Author(s):  
Paul Mueller
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
External Medium ◽  
Resting Potential ◽  
Prolonged Action ◽  
Nodes Of Ranvier ◽  
Duration Of Action ◽  
Na Ions ◽  
Cathodal Current ◽  
Kinetics Of

The duration of action potentials from single nodes of Ranvier can be increased by several methods. Extraction of water from the node (e.g. by 2 to 3 M glycerin) causes increased durations up to 1000 msec. 1 to 5 min. after application of the glycerin the duration of the action potential again decreases to the normal value. Another type of prolonged action potential can be observed in solutions which contain K or Rb ions at concentrations between 50 mM and 2 M. The nodes respond only if the resting potential is restored by anodal current. The kinetics of these action potentials is slightly different. Their maximal durations are longer (up to 10 sec.). Like the normal action potential, they are initiated by cathodal make or anodal break. They also occur in external solutions which contain no sodium. The same type of action potentials as in KCl is found when the node is depolarized for some time (15 to 90 sec., 100 to 200 mv.) and is then stimulated by cathodal current. These action potentials require no K or Na ions in the external medium. Their maximal duration increases with the strength and duration of the preceding depolarization. The possible origin of the action potentials in KCl and after depolarization, and their relation to the normal action potentials and the negative after-potential are discussed.

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