scholarly journals Shank promotes action potential repolarization by recruiting BK channels to calcium nanodomains

2021 ◽  
Author(s):  
Luna Gao ◽  
Jian Zhao ◽  
Evan L. Ardiel ◽  
Qi Hall ◽  
Stephen Nurrish ◽  
...  
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Gene Copy Number ◽  
Bk Channels ◽  
Scaffolding Protein ◽  
Gene Copy ◽  
Tight Coupling ◽  
C Elegans ◽  
Calcium Dependent ◽  
Action Potential Repolarization

Mutations altering the scaffolding protein Shank are linked to several psychiatric disorders, and to synaptic and behavioral defects in mice. Among its many binding partners, Shank directly binds CaV1 voltage activated calcium channels. Here we show that the C. elegans SHN-1/Shank promotes CaV1 coupling to calcium activated potassium channels. Mutations inactivating SHN-1, and those preventing SHN-1 binding to EGL-19/CaV1 all increase action potential durations in body muscles. Action potential repolarization is mediated by two classes of potassium channels: SHK-1/KCNA and SLO-1 and SLO-2 BK channels. BK channels are calcium-dependent, and their activation requires tight coupling to EGL-19/CaV1 channels. SHN-1’s effects on AP duration are mediated by changes in BK channels. In shn-1 mutants, SLO-2 currents and channel clustering are significantly decreased in both body muscles and neurons. Finally, increased and decreased shn-1 gene copy number produce similar changes in AP width and SLO-2 current. Collectively, these results suggest that an important function of Shank is to promote nanodomain coupling of BK with CaV1.

scholarly journals UNC-2 CaV2 channel localization at presynaptic active zones depends on UNC-10/RIM and SYD-2/Liprin-α in Caenorhabditis elegans

2021 ◽  
Author(s):  
Kelly H. Oh ◽  
Mia Krout ◽  
Janet E. Richmond ◽  
Hongkyun Kim
Keyword(s):  
Active Zone ◽  
Calcium Influx ◽  
Genetic Screen ◽  
Scaffolding Protein ◽  
Tight Coupling ◽  
Forward Genetic Screen ◽  
Precise Control ◽  
C Elegans ◽  
Vesicle Exocytosis ◽  
Active Zones

AbstractPresynaptic active zone proteins couple calcium influx with synaptic vesicle exocytosis. However, the control of presynaptic calcium channel clustering by active zone proteins is not completely understood. In a C. elegans forward genetic screen, we find that UNC-10/RIM (Rab3-interacting molecule) and SYD-2/Liprin-α regulate presynaptic clustering of UNC-2, the CaV2 channel ortholog. We further quantitatively analyzed live animals using endogenously GFP-tagged UNC-2 and active zone components. Consistent with the interaction between RIM and CaV2 in mammals, the intensity and number of UNC-2 channel clusters at presynaptic terminals were greatly reduced in unc-10 mutant animals. To understand how SYD-2 regulates presynaptic UNC-2 channel clustering, we analyzed presynaptic localization of endogenous SYD-2, UNC-10, RIMB-1/RIM-BP (RIM binding protein), and ELKS-1. Our analysis revealed that while SYD-2 is the most critical for active zone assembly, loss of SYD-2 function does not completely abolish presynaptic localization of UNC-10, RIMB-1, and ELKS-1, suggesting an existence of SYD-2-independent active zone assembly. UNC-2 localization analysis in double and triple mutants of active zone components show that SYD-2 promotes UNC-2 clustering by partially controlling UNC-10 localization, and ELKS-1 and RIMB-1 also contribute to UNC-2 channel clustering. In addition, we find that core active zone proteins are unequal in their abundance. While the abundance of UNC-10 at the active zone is comparable to UNC-2, SYD-2 and ELKS-1 are twice more and RIMB-1 four times more abundant than UNC-2. Together our data show that UNC-10, SYD-2, RIMB-1, and ELKS-1 control presynaptic UNC-2 channel clustering in redundant yet distinct manners.Significance StatementPrecise control of neurotransmission is dependent on the tight coupling of the calcium influx through voltage-gated calcium channels (VGCCs) to the exocytosis machinery at the presynaptic active zones. However, how these VGCCs are tethered to the active zone is incompletely understood. To understand the mechanism of presynaptic VGCC localization, we performed a C. elegans forward genetic screen and quantitatively analyzed endogenous active zones and presynaptic VGCCs. In addition to RIM (Rab3-interacting molecule), our study finds that SYD-2/Liprin-α is critical for presynaptic localization of VGCCs. Yet, the loss of SYD-2, the master active zone scaffolding protein, does not completely abolish the presynaptic localization of the VGCC, showing that the active zone is a resilient structure assembled by redundant mechanisms.

scholarly journals Ceramide modulates HERG potassium channel gating by translocation into lipid rafts

2010 ◽  
Vol 299 (1) ◽  
pp. C74-C86 ◽  
Author(s):  
Sindura B. Ganapathi ◽  
Todd E. Fox ◽  
Mark Kester ◽  
Keith S. Elmslie
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Lipid Rafts ◽  
Negative Impact ◽  
Cardiac Action Potential ◽  
Cholesterol Depletion ◽  
Cardiac Action ◽  
Herg Channels ◽  
The Impact ◽  
Action Potential Repolarization

Human ether-à-go-go-related gene (HERG) potassium channels play an important role in cardiac action potential repolarization, and HERG dysfunction can cause cardiac arrhythmias. However, recent evidence suggests a role for HERG in the proliferation and progression of multiple types of cancers, making it an attractive target for cancer therapy. Ceramide is an important second messenger of the sphingolipid family, which due to its proapoptotic properties has shown promising results in animal models as an anticancer agent . Yet the acute effects of ceramide on HERG potassium channels are not known. In the present study we examined the effects of cell-permeable C6-ceramide on HERG potassium channels stably expressed in HEK-293 cells. C6-ceramide (10 μM) reversibly inhibited HERG channel current (IHERG) by 36 ± 5%. Kinetically, ceramide induced a significant hyperpolarizing shift in the current-voltage relationship (Δ V1/2 = −8 ± 0.5 mV) and increased the deactivation rate (43 ± 3% for τfast and 51 ± 3% for τslow). Mechanistically, ceramide recruited HERG channels within caveolin-enriched lipid rafts. Cholesterol depletion and repletion experiments and mathematical modeling studies confirmed that inhibition and gating effects are mediated by separate mechanisms. The ceramide-induced hyperpolarizing gating shift (raft mediated) could offset the impact of inhibition (raft independent) during cardiac action potential repolarization, so together they may nullify any negative impact on cardiac rhythm. Our results provide new insights into the effects of C6-ceramide on HERG channels and suggest that C6-ceramide can be a promising therapeutic for cancers that overexpress HERG.

scholarly journals Inhibition of Ca2+-activated large-conductance K+ channel activity alters synaptic AMPA receptor phenotype in mouse cerebellar stellate cells

2011 ◽  
Vol 106 (1) ◽  
pp. 144-152 ◽  
Author(s):  
Yu Liu ◽  
Iaroslav Savtchouk ◽  
Shoana Acharjee ◽  
Siqiong June Liu
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Action Potential Duration ◽  
Action Potentials ◽  
Channel Blocker ◽  
Stellate Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Duration Of Action

Many fast-spiking inhibitory interneurons, including cerebellar stellate cells, fire brief action potentials and express α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors (AMPAR) that are permeable to Ca2+ and do not contain the GluR2 subunit. In a recent study, we found that increasing action potential duration promotes GluR2 gene transcription in stellate cells. We have now tested the prediction that activation of potassium channels that control the duration of action potentials can suppress the expression of GluR2-containing AMPARs at stellate cell synapses. We find that large-conductance Ca2+-activated potassium (BK) channels mediate a large proportion of the depolarization-evoked noninactivating potassium current in stellate cells. Pharmacological blockade of BK channels prolonged the action potential duration in postsynaptic stellate cells and altered synaptic AMPAR subtype from GluR2-lacking to GluR2-containing Ca2+-impermeable AMPARs. An L-type channel blocker abolished an increase in Ca2+ entry that was associated with spike broadening and also prevented the BK channel blocker-induced switch in AMPAR phenotype. Thus blocking BK potassium channels prolongs the action potential duration and increases the expression of GluR2-containing receptors at the synapse by enhancing Ca2+ entry in cerebellar stellate cells.

Increased or Decreased Levels of Caenorhabditis elegans lon-3, a Gene Encoding a Collagen, Cause Reciprocal Changes in Body Length

Genetics ◽  
2002 ◽  
Vol 161 (1) ◽  
pp. 83-97 ◽  
Author(s):  
Josefin Nyström ◽  
Zai-Zhong Shen ◽  
Margareta Aili ◽  
Anthony J Flemming ◽  
Armand Leroi ◽  
...  
Keyword(s):  
Body Length ◽  
Gene Copy Number ◽  
Gene Copy ◽  
Loss Of Function ◽  
Gene Encoding ◽  
C Elegans ◽  
Morphometric Analyses ◽  
Genes Encoding ◽  
New Mutations

Abstract Body length in C. elegans is regulated by a member of the TGFβ family, DBL-1. Loss-of-function mutations in dbl-1, or in genes encoding components of the signaling pathway it activates, cause worms to be shorter than wild type and slightly thinner (Sma). Overexpression of dbl-1 confers the Lon phenotype characterized by an increase in body length. We show here that loss-of-function mutations in dbl-1 and lon-1, respectively, cause a decrease or increase in the ploidy of nuclei in the hypodermal syncytial cell, hyp7. To learn more about the regulation of body length in C. elegans we carried out a genetic screen for new mutations causing a Lon phenotype. We report here the cloning and characterization of lon-3. lon-3 is shown to encode a putative cuticle collagen that is expressed in hypodermal cells. We show that, whereas putative null mutations in lon-3 (or reduction of lon-3 activity by RNAi) causes a Lon phenotype, increasing lon-3 gene copy number causes a marked reduction in body length. Morphometric analyses indicate that the lon-3 loss-of-function phenotype resembles that caused by overexpression of dbl-1. Furthermore, phenotypes caused by defects in dbl-1 or lon-3 expression are in both cases suppressed by a null mutation in sqt-1, a second cuticle collagen gene. However, whereas loss of dbl-1 activity causes a reduction in hypodermal endoreduplication, the reduction in body length associated with overexpression of lon-3 occurs in the absence of defects in hypodermal ploidy.

scholarly journals ERG-28 controls BK channel trafficking in the ER to regulate synaptic function and alcohol response in C. elegans

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Kelly H Oh ◽  
James J Haney ◽  
Xiaohong Wang ◽  
Chiou-Fen Chuang ◽  
Janet E Richmond ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Neurotransmitter Release ◽  
Calcium Influx ◽  
Bk Channels ◽  
Bk Channel ◽  
Synaptic Function ◽  
Neural Function ◽  
Channel Trafficking ◽  
C Elegans ◽  
Calcium Dependent

Voltage- and calcium-dependent BK channels regulate calcium-dependent cellular events such as neurotransmitter release by limiting calcium influx. Their plasma membrane abundance is an important factor in determining BK current and thus regulation of calcium-dependent events. In C. elegans, we show that ERG-28, an endoplasmic reticulum (ER) membrane protein, promotes the trafficking of SLO-1 BK channels from the ER to the plasma membrane by shielding them from premature degradation. In the absence of ERG-28, SLO-1 channels undergo aspartic protease DDI-1-dependent degradation, resulting in markedly reduced expression at presynaptic terminals. Loss of erg-28 suppressed phenotypic defects of slo-1 gain-of-function mutants in locomotion, neurotransmitter release, and calcium-mediated asymmetric differentiation of the AWC olfactory neuron pair, and conferred significant ethanol-resistant locomotory behavior, resembling slo-1 loss-of-function mutants, albeit to a lesser extent. Our study thus indicates that the control of BK channel trafficking is a critical regulatory mechanism for synaptic transmission and neural function.

Regulation of Firing Response Gain by Calcium-Dependent Mechanisms in Vestibular Nucleus Neurons

2002 ◽  
Vol 87 (4) ◽  
pp. 2031-2042 ◽  
Author(s):  
Marianne R. Smith ◽  
Alexandra B. Nelson ◽  
Sascha du Lac
Keyword(s):  
Potassium Channels ◽  
Calcium Channels ◽  
Firing Rate ◽  
Vestibular Nucleus ◽  
Bk Channels ◽  
Extracellular Calcium ◽  
Medial Vestibular Nucleus ◽  
Sk Channels ◽  
Calcium Dependent ◽  
Wide Range

Behavioral reflexes can be modified by experience via mechanisms that are largely unknown. Within the circuitry for the vestibuloocular reflex (VOR), neurons in the medial vestibular nucleus (MVN) show adaptive changes in firing rate responses that are correlated with VOR gain (the ratio of evoked eye velocity to input head velocity). Although changes in synaptic strength are typically assumed to underlie gain changes in the VOR, modulation of intrinsic ion channels that dictate firing could also play a role. Little is known, however, about how ion channel function or regulation contributes to firing responses in MVN neurons. This study examined contributions of calcium-dependent currents to firing responses in MVN neurons recorded with whole cell patch electrodes in rodent brain stem slices. Firing responses were remarkably linear over a wide range of firing rates and showed modest spike frequency adaptation. Firing response gain, the ratio of evoked firing rate to input current, was reduced by increasing extracellular calcium and increased either by lowering extracellular calcium or with antagonists to SK- and BK-type calcium-dependent potassium channels and N- and T-type calcium channels. Blockade of SK channels occluded gain increases via N-type calcium channels, while blocking BK channels occluded gain increases via presumed T-type calcium channels, indicating specific coupling of potassium channels and their calcium sources. Selective inhibition of Ca2+/calmodulin-dependent kinase II and broad-spectrum inhibition of phosphatases modulated gain via BK-dependent pathways, indicating that firing responses are tightly regulated. Modulation of firing response gain by phosphorylation provides an attractive mechanism for adaptive control of VOR gain.

Calcium-dependent potassium channels play a critical role for burst termination in the locomotor network in lamprey

1994 ◽  
Vol 72 (4) ◽  
pp. 1852-1861 ◽  
Author(s):  
A. el Manira ◽  
J. Tegner ◽  
S. Grillner
Keyword(s):  
Spinal Cord ◽  
Potassium Channels ◽  
Action Potential ◽  
Slow Phase ◽  
Cycle Duration ◽  
Fictive Locomotion ◽  
Average Increase ◽  
Calcium Dependent ◽  
Locomotor Pattern ◽  
Kca Channels

1. The possible involvement of calcium-dependent potassium channels (KCa) in the termination of locomotor bursts was investigated by administration of a specific blocker, apamin, in the lamprey spinal cord in vitro. The effects were examined by recording the efferent activity in ventral roots and by intracellular recording from interneurons and motoneurons. During fictive locomotion induced by N-methyl-D-aspartate (NMDA), apamin was found to affect both the frequency of bursting and the regularity of the locomotor pattern. 2. At the single cell level, NMDA can induce pacemaker-like membrane potential oscillations in individual neurons after administration of tetrodotoxin. Apamin (2.5 microM) produced a marked increase of the duration of the depolarizing plateau phase occurring during these NMDA-induced oscillations; this shows that the repolarization of the plateau is initiated by a progressive activation of apamin-sensitive KCa-channels. 3. The action potential is followed by an afterhyperpolarization (AHP) with a fast and a slow phase (sAHP). The latter is known to be caused by apamin-sensitive KCa-channels. During repetitive firing, the interspike interval is dependent on the amplitude and the duration of the sAHP. Apamin caused a reduction of the spike frequency adaptation with a concomitant increase in the firing frequency. In some cells, apamin in addition reduced the threshold for the action potential. Apamin-sensitive KCa-channels thus will be involved in controlling both the onset and the duration of neuronal firing in the lamprey spinal cord. 4. During fictive locomotion induced by NMDA (40-200 microM), a blockade of KCa-channels by apamin produced an increase of the coefficient of variation (mean = 167%, n = 26), which was statistically significant in 21 out of 26 experiments. At 40-150 microM NMDA, an average increase in cycle duration was 77% and statistically significant in 15 out of 20 preparations. At 200 microM NMDA (corresponding to higher burst rate), on the other hand, the average increase was only 6% and the increase was statistically significant in only 1 out 6 cases. For a given experiment, the strength of the apamin effect depended on the level of NMDA drive used, being more pronounced at slow rhythms, when it often caused a complete disruption of the locomotor pattern. At high burst rates, however, the cycle duration was less affected and a disruption of the regular burst pattern did not occur.(ABSTRACT TRUNCATED AT 400 WORDS)

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