Faculty Opinions recommendation of Calcium-activated chloride channels (CaCCs) regulate action potential and synaptic response in hippocampal neurons.

Although extracellular Zn2+ is an endogenous biphasic modulator of strychnine-sensitive glycine receptors (GlyRs), the physiological significance of this modulation remains poorly understood. Zn2+ modulation of GlyR may be especially important in the hippocampus where presynaptic Zn2+ is abundant. Using cultured embryonic mouse hippocampal neurons, we examined whether 1 μM Zn2+, a potentiating concentration, enhances the inhibitory effects of GlyRs activated by sustained glycine applications. Sustained 20 μM glycine (EC25) applications alone did not decrease the number of action potentials evoked by depolarizing steps, but they did in 1 μM Zn2+. At least part of this effect resulted from Zn2+ enhancing the GlyR-induced decrease in input resistance. Sustained 20 μM glycine applications alone did not alter neuronal bursting, a form of hyperexcitability induced by omitting extracellular Mg2+. However, sustained 20 μM glycine applications depressed neuronal bursting in 1 μM Zn2+. Zn2+ did not enhance the inhibitory effects of sustained 60 μM glycine (EC70) applications in these paradigms. These results suggest that tonic GlyR activation could decrease neuronal excitability. To test this possibility, we examined the effect of the GlyR antagonist strychnine and the Zn2+ chelator tricine on action potential firing by CA1 pyramidal neurons in mouse hippocampal slices. Co-applying strychnine and tricine slightly but significantly increased the number of action potentials fired during a depolarizing current step and decreased the rheobase for action potential firing. Thus Zn2+ may modulate neuronal excitability normally and in pathological conditions such as seizures by potentiating GlyRs tonically activated by low agonist concentrations.

Download Full-text

Regulation of Action Potential Frequency and Amplitude by T-type Ca2+ Channel During Spontaneous Synchronous Activity of Hippocampal Neurons

BIOPHYSICS ◽

10.1134/s0006350918040206 ◽

2018 ◽

Vol 63 (4) ◽

pp. 566-575 ◽

Cited By ~ 2

Author(s):

I. Yu. Teplov ◽

S. T. Tuleukhanov ◽

V. P. Zinchenko

Keyword(s):

Action Potential ◽

Hippocampal Neurons ◽

Synchronous Activity ◽

Action Potential Frequency ◽

Potential Frequency

Download Full-text

α2-Adrenergic Receptor and Isoflurane Modulation of Presynaptic Ca2+ Influx and Exocytosis in Hippocampal Neurons

Anesthesiology ◽

10.1097/aln.0000000000001213 ◽

2016 ◽

Vol 125 (3) ◽

pp. 535-546 ◽

Cited By ~ 9

Author(s):

Masato Hara ◽

Zhen-Yu Zhou ◽

Hugh C. Hemmings

Keyword(s):

Action Potential ◽

Neurotransmitter Release ◽

Adrenergic Receptor ◽

Presynaptic Inhibition ◽

Hippocampal Neurons ◽

Quantitative Imaging ◽

Volatile Anesthetics ◽

Fluorescent Biosensors ◽

Selective Antagonist ◽

Ca2 Channels

Abstract Background Evidence indicates that the anesthetic-sparing effects of α2-adrenergic receptor (AR) agonists involve α2A-AR heteroreceptors on nonadrenergic neurons. Since volatile anesthetics inhibit neurotransmitter release by reducing synaptic vesicle (SV) exocytosis, the authors hypothesized that α2-AR agonists inhibit nonadrenergic SV exocytosis and thereby potentiate presynaptic inhibition of exocytosis by isoflurane. Methods Quantitative imaging of fluorescent biosensors of action potential–evoked SV exocytosis (synaptophysin-pHluorin) and Ca2+ influx (GCaMP6) were used to characterize presynaptic actions of the clinically used α2-AR agonists dexmedetomidine and clonidine, and their interaction with isoflurane, in cultured rat hippocampal neurons. Results Dexmedetomidine (0.1 μM, n = 10) or clonidine (0.5 μM, n = 8) inhibited action potential–evoked exocytosis (54 ± 5% and 59 ± 8% of control, respectively; P < 0.001). Effects on exocytosis were blocked by the subtype-nonselective α2-AR antagonist atipamezole or the α2A-AR–selective antagonist BRL 44408 but not by the α2C-AR–selective antagonist JP 1302. Dexmedetomidine inhibited exocytosis and presynaptic Ca2+ influx without affecting Ca2+ coupling to exocytosis, consistent with an effect upstream of Ca2+–exocytosis coupling. Exocytosis coupled to both N-type and P/Q-type Ca2+ channels was inhibited by dexmedetomidine or clonidine. Dexmedetomidine potentiated inhibition of exocytosis by 0.7 mM isoflurane (to 42 ± 5%, compared to 63 ± 8% for isoflurane alone; P < 0.05). Conclusions Hippocampal SV exocytosis is inhibited by α2A-AR activation in proportion to reduced Ca2+ entry. These effects are additive with those of isoflurane, consistent with a role for α2A-AR presynaptic heteroreceptor inhibition of nonadrenergic synaptic transmission in the anesthetic-sparing effects of α2A-AR agonists.

Download Full-text

Polarized localization of voltage-gated Na+ channels is regulated by concerted FGF13 and FGF14 action

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1521194113 ◽

2016 ◽

Vol 113 (19) ◽

pp. E2665-E2674 ◽

Cited By ~ 33

Author(s):

Juan Lorenzo Pablo ◽

Chaojian Wang ◽

Matthew M. Presby ◽

Geoffrey S. Pitt

Keyword(s):

Action Potential ◽

Hippocampal Neurons ◽

Single Point ◽

Point Mutations ◽

Surface Expression ◽

Voltage Gated ◽

Voltage Gated Sodium Channels ◽

Action Potential Initiation ◽

Potential Initiation

Clustering of voltage-gated sodium channels (VGSCs) within the neuronal axon initial segment (AIS) is critical for efficient action potential initiation. Although initially inserted into both somatodendritic and axonal membranes, VGSCs are concentrated within the axon through mechanisms that include preferential axonal targeting and selective somatodendritic endocytosis. How the endocytic machinery specifically targets somatic VGSCs is unknown. Here, using knockdown strategies, we show that noncanonical FGF13 binds directly to VGSCs in hippocampal neurons to limit their somatodendritic surface expression, although exerting little effect on VGSCs within the AIS. In contrast, homologous FGF14, which is highly concentrated in the proximal axon, binds directly to VGSCs to promote their axonal localization. Single-point mutations in FGF13 or FGF14 abrogating VGSC interaction in vitro cannot support these specific functions in neurons. Thus, our data show how the concerted actions of FGF13 and FGF14 regulate the polarized localization of VGSCs that supports efficient action potential initiation.

Download Full-text

Direct Actions of Carbenoxolone on Synaptic Transmission and Neuronal Membrane Properties

Journal of Neurophysiology ◽

10.1152/jn.00060.2009 ◽

2009 ◽

Vol 102 (2) ◽

pp. 974-978 ◽

Cited By ~ 82

Author(s):

Kenneth R. Tovar ◽

Brady J. Maher ◽

Gary L. Westbrook

Keyword(s):

Action Potential ◽

Synaptic Transmission ◽

Gap Junctions ◽

Hippocampal Neurons ◽

Electrical Coupling ◽

Network Activity ◽

Membrane Properties ◽

Neuronal Membrane ◽

Postsynaptic Currents ◽

Gap Junctional

The increased appreciation of electrical coupling between neurons has led to many studies examining the role of gap junctions in synaptic and network activity. Although the gap junctional blocker carbenoxolone (CBX) is effective in reducing electrical coupling, it may have other actions as well. To study the non–gap junctional effects of CBX on synaptic transmission, we recorded from mouse hippocampal neurons cultured on glial micro-islands. This recording configuration allowed us to stimulate and record excitatory postsynaptic currents (EPSCs) or inhibitory postsynaptic currents (IPSCs) in the same neuron or pairs of neurons. CBX irreversibly reduced evoked α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid (AMPA) receptor–mediated EPSCs. Consistent with a presynaptic site of action, CBX had no effect on glutamate-evoked whole cell currents and increased the paired-pulse ratio of AMPA and N-methyl-d-aspartate (NMDA) receptor–mediated EPSCs. CBX also reversibly reduced GABAA receptor–mediated IPSCs, increased the action potential width, and reduced the action potential firing rate. Our results indicate CBX broadly affects several neuronal membrane conductances independent of its effects on gap junctions. Thus effects of carbenoxolone on network activity cannot be interpreted as resulting from specific block of gap junctions.

Download Full-text

Calcium stores regulate excitability in cultured rat hippocampal neurons

Journal of Neurophysiology ◽

10.1152/jn.00447.2018 ◽

2018 ◽

Vol 120 (5) ◽

pp. 2694-2705 ◽

Cited By ~ 6

Author(s):

Menahem Segal

Keyword(s):

Action Potential ◽

Hippocampal Neurons ◽

Extracellular Calcium ◽

Calcium Stores ◽

Sk Channels ◽

Central Neurons ◽

Action Potential Threshold ◽

Potential Threshold ◽

Small Conductance ◽

Cultured Hippocampal Neurons

Extracellular calcium ions support synaptic activity but also reduce excitability of central neurons. In the present study, the effect of calcium on excitability was explored in cultured hippocampal neurons. CaCl2 injected by pressure in the vicinity of a neuron that is bathed only in MgCl2 as the main divalent cation caused a depolarizing shift in action potential threshold and a reduction in excitability. This effect was not seen if the intracellular milieu consisted of Cs+ instead of K-gluconate as the main cation or when it contained ruthenium red, which blocks release of calcium from stores. The suppression of excitability by calcium was mimicked by caffeine, and calcium store antagonists cyclopiazonic acid or thapsigargin blocked this action. Neurons taken from synaptopodin-knockout mice show significantly reduced efficacy of calcium modulation of action potential threshold. Likewise, in Orai1 knockdown cells, calcium is less effective in modulating excitability of neurons. Activation of small-conductance K (SK) channels increased action potential threshold akin to that produced by calcium ions, whereas blockade of SK channels but not big K channels reduced the threshold for action potential discharge. These results indicate that calcium released from stores may suppress excitability of central neurons. NEW & NOTEWORTHY Extracellular calcium reduces excitability of cultured hippocampal neurons. This effect is mediated by calcium-gated potassium currents, possibly small-conductance K channels. Release of calcium from internal stores mimics the effect of extracellular calcium. It is proposed that calcium stores modulate excitability of central neurons.

Download Full-text

BK current contributions to action potentials across the first postnatal week reflect age dependent changes in BK current kinetics in rat hippocampal neurons

10.1101/839233 ◽

2019 ◽

Author(s):

Michael Hunsberger ◽

Michelle Mynlieff

Keyword(s):

Action Potential ◽

Action Potentials ◽

Hippocampal Neurons ◽

Expression Patterns ◽

Bk Channels ◽

Bk Channel ◽

Action Potential Firing ◽

Developmental Trends ◽

Channel Expression ◽

Old Rats

AbstractThe large conductance calcium-activated potassium (BK) channel is a critical regulator of neuronal action potential firing and follows two distinct trends in early postnatal development: an increase in total expression and a shift from the faster activating STREX isoform to the slower ZERO isoform. We analyzed the functional consequences of developmental trends in BK channel expression in hippocampal neurons isolated from neonatal rats aged one to seven days. Following overnight cultures, action potentials were recorded using whole-cell patch clamp electrophysiology. This population of neurons undergoes a steady increase in excitability during this time and the effect of blockade of BK channel activity with 100 nM iberiotoxin, changes as the neurons mature. BK currents contribute significantly more to single action potentials in neurons of one-day old rats (with BK blockade extending action potential duration by 0.46±0.12 ms) than in those of seven-day old rats (with BK blockade extending action potential duration by 0.17±0.05 ms). BK currents also contribute consistently to maintain firing rates in neurons of one-day old rats throughout extended action potential firing; BK blockade evenly depresses action potentials frequency across action potential trains. In neurons from seven-day old rats, BK blockade initially increases firing frequency and then progressively decreases frequency as firing continues, ultimately depressing neuronal firing rates to a greater extent than in the neurons from one day old animals. These results are consistent with a transition from low expression of a fast activating BK isoform (STREX) to high expression of a slower activating isoform (ZERO).New and NoteworthyThis work describes the early developmental trends of BK channel activity. Early developmental trends in expression of BK channels, both total expression and relative isoform expression, have been previously reported, but little work describes the effect of these changes in expression patterns on excitability. Here, we show that early changes in BK channel expression patterns lead to changes in the role of BK channels in determining the action potential waveform and neuronal excitability.

Download Full-text

Altered Chloride Homeostasis Decreases the Action Potential Threshold and Increases Hyperexcitability in Hippocampal Neurons

eNeuro ◽

10.1523/eneuro.0172-17.2017 ◽

2017 ◽

Vol 4 (6) ◽

pp. ENEURO.0172-17.2017 ◽

Cited By ~ 10

Author(s):

Andreas T. Sørensen ◽

Marco Ledri ◽

Miriam Melis ◽

Litsa Nikitidou Ledri ◽

My Andersson ◽

...

Keyword(s):

Action Potential ◽

Hippocampal Neurons ◽

Chloride Homeostasis ◽

Action Potential Threshold ◽

Potential Threshold

Download Full-text

Electrophysiological Roles of L-Type Channels in Different Classes of Guinea Pig Sympathetic Neuron

Journal of Neurophysiology ◽

10.1152/jn.1999.82.2.818 ◽

1999 ◽

Vol 82 (2) ◽

pp. 818-828 ◽

Cited By ~ 14

Author(s):

Philip J. Davies ◽

David R. Ireland ◽

Juan Martinez-Pinna ◽

Elspeth M. McLachlan

Keyword(s):

Guinea Pig ◽

Action Potential ◽

Hippocampal Neurons ◽

Sympathetic Ganglia ◽

Bk Channels ◽

Half Width ◽

Sk Channels ◽

Single Action ◽

Ganglion Neurons

The electrophysiological consequences of blocking Ca2+ entry through L-type Ca2+ channels have been examined in phasic ( Ph), tonic ( T), and long-afterhyperpolarizing ( LAH) neurons of intact guinea pig sympathetic ganglia isolated in vitro. Block of Ca2+entry with Co2+ or Cd2+ depolarized T and LAH neurons, reduced action potential (AP) amplitude in Ph and LAHneurons, and increased AP half-width in Ph neurons. The afterhyperpolarization (AHP) and underlying Ca2+-dependent K+ conductances ( gKCa1 and gKCa2) were reduced markedly in all classes. Addition of 10 μM nifedipine increased input resistance in LAHneurons, raised AP threshold in Ph and LAH neurons, and caused a small increase in AP half-width in Ph neurons. AHP amplitude and the amplitude and decay time constant of gKCa1 were reduced by nifedipine in all classes; the slower conductance, gKCa2, which underlies the prolonged AHP in LAH neurons, was reduced by 40%. Surprisingly, AHP half-width was lengthened by nifedipine in a proportion of neurons in all classes; despite this, neuron excitability was increased during a maintained depolarization. Nifedipine’s effects on AHP half-width were not mimicked by 2 mM Cs+ or 2 mM anthracene-9-carboxylic acid, a blocker of Cl− channels, and it did not modify transient outward currents of the A or D types. The effects of 100 μM Ni2+ differed from those of nifedipine. Thus in Ph neurons, Ca2+ entry through L-type channels during a single action potential contributes to activation of K+ conductances involved in both the AP and AHP, whereas in T and LAH neurons, it acts only on gKCa1 and gKCa2. These results differ from the results in rat superior cervical ganglion neurons, in which L-type channels are selectively coupled to BK channels, and in hippocampal neurons, in which L-type channels are selectively coupled to SK channels. We conclude that the sources of Ca2+ for activating the various Ca2+-activated K+conductances are distinct in different types of neuron.

Download Full-text