scholarly journals Maternal Diabetes Increases Small Conductance Ca2+-Activated K+ (SK) Currents That Alter Action Potential Properties and Excitability of Cardiac Motoneurons in the Nucleus Ambiguus

2010 ◽  
Vol 104 (4) ◽  
pp. 2125-2138 ◽  
Author(s):  
Min Lin ◽  
Qing-Hui Chen ◽  
Robert D. Wurster ◽  
Jeff T. Hatcher ◽  
Ye-Qi Liu ◽  
...  
Keyword(s):  
Action Potential ◽  
Firing Rate ◽  
Maternal Diabetes ◽  
Spike Frequency ◽  
Nucleus Ambiguus ◽  
Peak Amplitude ◽  
Sk Channels ◽  
Transient Currents ◽  
Whole Cell ◽  
Small Conductance

Parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) play a key role in regulating cardiac functions. In this study, we examined the effects of maternal diabetes on excitability, action potential (AP) properties, and small conductance Ca2+-activated K+ (SK) currents of PCMNs. Neonatal mice from diabetic (OVE26 female, NMDM) and normal (FVB female, control) mothers that had been mated with nondiabetic fathers (FVB male) were used. Tracer XRITC was injected into the pericardial sac at P7-9 to retrogradely label PCMNs. Two days later, XRITC-labeled PCMNs were identified in brain stem slices. The responses of spike frequency, AP repolarization (half-width) and afterhyperpolarization (AHP) of PCMNs to current injections were studied using whole cell current clamp. Outward and afterhyperpolarization currents ( IAHP) in response to voltage steps were measured using whole cell voltage clamp. In examining the effects of maternal diabetes on excitability and AP properties, we found that in NMDM spike frequency decreased, the half-width and AHP peak amplitude increased, and the peak amplitude of outward transient currents and IAHP increased compared with those measured in control. In examining the effects of maternal diabetes on SK channels, we found that after blockage of SK channels with a specific SK channel blocker apamin, maternal diabetes significantly increased apamin-sensitive outward transient currents and IAHP, and suppressed AHP amplitude in NMDM more than those in control. Further, apamin application increased the firing rate to current injections and completely abolished the difference of the firing rate between control and NMDM. We suggest that the augmented SK-mediated currents may contribute to the increased AHP amplitude and the attenuated excitability of PCMNs in NMDM.

scholarly journals Small conductance Ca2+-activated K+ channels regulate firing properties and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus

2010 ◽  
Vol 299 (6) ◽  
pp. C1285-C1298 ◽  
Author(s):  
Min Lin ◽  
Jeff T. Hatcher ◽  
Qin-Hui Chen ◽  
Robert D. Wurster ◽  
Zixi (Jack) Cheng
Keyword(s):  
Negative Control ◽  
Spike Frequency ◽  
Nucleus Ambiguus ◽  
Sk Channels ◽  
Channel Blockade ◽  
Whole Cell ◽  
Sk Channel ◽  
Outward Currents ◽  
Firing Properties ◽  
Small Conductance

Small conductance Ca2+-activated K+ channels (SK) regulate action potential (AP) firing properties and excitability in many central neurons. However, the functional roles of SK channels of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal days 7–9. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. With the use of whole cell current clamp, single APs and spike trains of different frequencies were evoked by current injections. We found that 1) PCMNs have two different firing patterns: the majority of PCMNs (90%) exhibited spike frequency adaptation (SFA) and the rest (10%) showed less or no adaptation; 2) application of the specific SK channel blocker apamin significantly increased spike half-width in single APs and trains and reduced the spike frequency-dependent AP broadening in trains; 3) SK channel blockade suppressed afterhyperpolarization (AHP) amplitude following single APs and trains and abolished spike-frequency dependence of AHP in trains; and 4) SK channel blockade increased the spike frequency but did not alter the pattern of SFA. Using whole cell voltage clamp, we measured outward currents and afterhyperpolarization current ( IAHP). SK channel blockade revealed that SK-mediated outward currents had both transient and persistent components. After bath application of apamin and Ca2+-free solution, we found that apamin-sensitive and Ca2+-sensitive IAHP were comparable, confirming that SK channels may contribute to a major portion of Ca2+-activated K+ channel-mediated IAHP. These results suggest that PCMNs have SK channels that significantly regulate AP repolarization, AHP, and spike frequency but do not affect SFA. We conclude that activation of SK channels underlies one of the mechanisms for negative control of PCMN excitability.

scholarly journals Maternal diabetes increases large conductance Ca2+-activated K+ outward currents that alter action potential properties but do not contribute to attenuated excitability of parasympathetic cardiac motoneurons in the nucleus ambiguus of neonatal mice

2011 ◽  
Vol 300 (5) ◽  
pp. R1070-R1078 ◽  
Author(s):  
Min Lin ◽  
Jeff T. Hatcher ◽  
Qing-Hui Chen ◽  
Robert D. Wurster ◽  
Lihua Li ◽  
...  
Keyword(s):  
Maternal Diabetes ◽  
Bk Channels ◽  
Spike Frequency ◽  
Half Width ◽  
Nucleus Ambiguus ◽  
Whole Cell ◽  
Neonatal Mice ◽  
Outward Currents ◽  
Cell Current ◽  
Diabetic Mothers

Previously, we demonstrated that maternal diabetes reduced the excitability and increased small-conductance Ca2+-activated K+ (SK) currents of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA). In addition, blockade of SK channels with apamin completely abolished this reduction. In the present study, we examined whether maternal diabetes affects large-conductance Ca2+-activated K+ (BK) channels and whether BK channels contribute to the attenuation of PCMN excitability observed in neonates of diabetic mothers. Neonatal mice from OVE26 diabetic mothers (NMDM) and normal FVB mothers (control) were used. The pericardial sac of neonatal mice at postnatal days 7–9 was injected with the tracer X-rhodamine-5 (and 6)-isothiocyanate 2 days prior to the experiment to retrogradely label PCMNs in the NA. Whole cell current- and voltage-clamps were used to measure spike frequency, action potential (AP) repolarization (half-width), afterhyperpolarization potential (AHP), transient outward currents, and afterhyperpolarization currents ( IAHP). In whole cell voltage clamp mode, we confirmed that maternal diabetes increased transient outward currents and IAHP compared with normal cells. Using BK channel blockers charybdotoxin (CTx) and paxilline, we found that maternal diabetes increased CTx- and paxilline-sensitive transient outward currents but did not change CTx- and paxilline-sensitive IAHP. In whole cell current-clamp mode, we confirmed that maternal diabetes increased AP half-width and AHP, and reduced excitability of PCMNs. Furthermore, we found that after blockade of BK channels with CTx or paxilline, maternal diabetes induced a greater increase of AP half-width but similarly decreased fast AHP without affecting medium AHP. Finally, blockade of BK channels decreased spike frequency in response to current injection in both control and NMDM without reducing the difference of spike frequency between the two groups. Therefore, we conclude that although BK transient outward currents, which may alter AP repolarization, are increased in NMDM, BK channels do not directly contribute to maternal diabetes-induced attenuation of PCMN excitability. In contrast, based on evidence from our previous and present studies, reduction of PCMN excitability in neonates of diabetic mothers is largely dependent on altered SK current associated with maternal diabetes.

Pharmacological Modulation of the Gating Properties of Small Conductance Ca2+-Activated K+ Channels Alters the Firing Pattern of Dopamine Neurons In Vivo

2010 ◽  
Vol 104 (3) ◽  
pp. 1726-1735 ◽  
Author(s):  
Kjartan F. Herrik ◽  
Palle Christophersen ◽  
Paul D. Shepard
Keyword(s):  
Firing Rate ◽  
Dopamine Neurons ◽  
Substantia Nigra Pars Compacta ◽  
Pacemaker Activity ◽  
Sk Channels ◽  
Pharmacological Modulation ◽  
Sk Channel ◽  
Discharge Patterns ◽  
Small Conductance

Dopamine (DA) neurons are autonomous pacemakers that occasionally fire bursts of action potentials, discharge patterns thought to reflect tonic and phasic DA signaling, respectively. Pacemaker activity depends on the concerted and cyclic interplay between intrinsic ion channels with small conductance Ca2+-activated K+ (SK) channels playing an important role. Bursting activity is synaptically initiated but neither the transmitters nor the specific ion conductances involved have been definitively identified. Physiological and pharmacological regulation of SK channel Ca2+ sensitivity has recently been demonstrated and could represent a powerful means of modulating the expression of tonic/phasic signaling in DA neurons in vivo. To test this premise, we characterized the effects of intravenous administration of the novel positive and negative SK channel modulators NS309 and NS8593, respectively, on the spontaneous activity of substantia nigra pars compacta DA neurons in anesthetized C57BL/6 mice. NS309, dose-dependently decreased DA cell firing rate, increased the proportion of regular firing cells, and eventually stopped spontaneous firing. By contrast, systemic administration of the negative SK channel modulator NS8593 increased firing rate and shifted the pattern toward increased irregularity/bursting; an effect similar to local application of the pore blocking peptide apamin. The altered firing patterns resulting from inhibiting SK currents persisted independently of changes in firing rates induced by administration of DA autoreceptor agonists/antagonists. We conclude that pharmacological modulation of SK channel Ca2+-sensitivity represents a powerful mechanism for switching DA neuron firing activity between tonic and phasic signaling modalities in vivo.

scholarly journals Small-conductance calcium-activated potassium (SK) channels contribute to action potential repolarization in human atria

2014 ◽  
Vol 103 (1) ◽  
pp. 156-167 ◽  
Author(s):  
Lasse Skibsbye ◽  
Claire Poulet ◽  
Jonas Goldin Diness ◽  
Bo Hjorth Bentzen ◽  
Lei Yuan ◽  
...  
Keyword(s):  
Action Potential ◽  
Sk Channels ◽  
Action Potential Repolarization ◽  
Small Conductance

scholarly journals Calcium stores regulate excitability in cultured rat hippocampal neurons

2018 ◽  
Vol 120 (5) ◽  
pp. 2694-2705 ◽  
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.

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 Characteristics of single large-conductance Ca2+-activated K+ channels and their regulation of action potentials and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus

2014 ◽  
Vol 306 (2) ◽  
pp. C152-C166 ◽  
Author(s):  
Min Lin ◽  
Jeff T. Hatcher ◽  
Robert D. Wurster ◽  
Qin-Hui Chen ◽  
Zixi (Jack) Cheng
Keyword(s):  
Single Channel ◽  
Cell Voltage ◽  
Bk Channels ◽  
Bk Channel ◽  
Spike Frequency ◽  
Half Width ◽  
Nucleus Ambiguus ◽  
Whole Cell ◽  
Channel Opening ◽  
Channel Open Time

Large-conductance Ca2+-activated K+ channels (BK) regulate action potential (AP) properties and excitability in many central neurons. However, the properties and functional roles of BK channels in parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal 7–9 days. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. Using excised patch single-channel recordings, we identified voltage-gated and Ca2+-dependent BK channels in PCMNs. The majority of BK channels exhibited persistent channel opening during voltage holding. These BK channels had a conductance of 237 pS and a 50% opening probability at +27.9 mV, the channel open time constant was 3.37 ms at +20 mV, and dwell time increased exponentially as the membrane potential depolarized. At the +20-mV holding potential, the [Ca2+]50 was 15.2 μM with a P0.5 of 0.4. Occasionally, some BK channels showed a transient channel opening and fast inactivation. Using whole cell voltage clamp, we found that BK channel mediated outward currents and afterhyperpolarization currents ( IAHP). Using whole cell current clamp, we found that application of BK channel blocker iberiotoxin (IBTX) increased spike half-width and suppressed fast afterhyperpolarization (fAHP) amplitude following single APs. In addition, IBTX application increased spike half-width and reduced the spike frequency-dependent AP broadening in trains and spike frequency adaption (SFA). Furthermore, BK channel blockade decreased spike frequency. Collectively, these results demonstrate that PCMNs have BK channels that significantly regulate AP repolarization, fAHP, SFA, and spike frequency. We conclude that activation of BK channels underlies one of the mechanisms for facilitation of PCMN excitability.

scholarly journals Inhibition of Small-Conductance, Ca2+-Activated K+ Current by Ondansetron

2021 ◽  
Vol 12 ◽  
Author(s):  
Shuai Guo ◽  
Zhenhui Chen ◽  
Peng-Sheng Chen ◽  
Michael Rubart
Keyword(s):  
Inhibitory Effect ◽  
Sk Channels ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Hek 293 ◽  
Hek 293 Cells ◽  
Whole Cell Patch Clamp ◽  
293 Cells ◽  
Inwardly Rectifying ◽  
Small Conductance

Background: Small-conductance Ca2+-activated K+ channels (SK channels) have been proposed as antiarrhythmic targets for the treatment of atrial fibrillation. We previously demonstrated that the 5-HT3 receptor antagonist ondansetron inhibits heterologously expressed, human SK2 (hSK2) currents as well as native cardiac SK currents in a physiological extra-/intracellular [K+] gradient at therapeutic (i.e., sub-micromolar) concentrations. A recent study, using symmetrical [K+] conditions, challenged this result. The goal of the present study was to revisit the inhibitory effect of ondansetron on hSK2-mediated currents in symmetrical [K+] conditions.Experimental Approach: The whole-cell patch clamp technique was used to investigate the effects of ondansetron and apamin on hSK2-mediated currents expressed in HEK 293 cells. Currents were measured in symmetrical [K+] conditions in the presence of 100 nM [Ca2+]o.Results: Expression of hSK2 produced inwardly rectifying whole-cell currents in the presence of 400 nM free cytosolic Ca2+. Ondansetron inhibited whole-cell hSK2 currents with IC50 values of 154 and 113 nM at −80 and 40 mV, respectively. Macroscopic current inhibited by ondansetron and current inhibited by apamin exhibited inwardly rectifying current-voltage relationships with similar reversal potentials (apamin, ∼5 mV and ondansetron, ∼2 mV). Ondansetron (1 μM) in the continuing presence of apamin (100 nM) had no effect on hSK2-mediated whole-cell currents. Wild-type HEK 293 cells did not express ondansetron- or apamin-sensitive currents.Conclusion: Ondansetron in sub-micromolar concentrations inhibits hSK2 currents even under altered ionic conditions.

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