Slow recovery from fast inactivation of Nav1.3 channels: a common gating mechanism shared in sweet- and sour-sensing cells

2021 ◽  
Author(s):  
Christopher J. Lingle
Keyword(s):  
Fast Inactivation ◽  
Slow Recovery ◽  
Gating Mechanism

Two conformational states involved in the use-dependent TTX blockade of human cardiac Na+ channel

1996 ◽  
Vol 270 (6) ◽  
pp. H2029-H2037 ◽  
Author(s):  
R. Dumaine ◽  
H. A. Hartmann
Keyword(s):  
Direct Interaction ◽  
Na Channel ◽  
Fast Inactivation ◽  
Slow Recovery ◽  
Similar Time ◽  
Activated State ◽  
High Affinity Site ◽  
Action Potential Plateau ◽  
Time Courses ◽  
High Concentrations

We used a fast inactivation-deficient mutant (QQQ) of the human heart Na+ channel alpha-subunit (hH1a) to assess the influence of the inactivation gate on tetrodotoxin (TTX) use-dependent block (UDB) and postrepolarization block (PRB). PRB had similar time courses in both channels, suggesting no direct interaction of the inactivation gate with the TTX binding site. The UDB saturated with high concentrations of TTX in hH1a but not in QQQ, revealing the modulatory action of fast inactivation on UDB. TTX did not stabilize the inactivated states of QQQ, and the extra block developing during long depolarizations suggests a higher-affinity site involved in the gating of the channel. These results cannot be solely explained by a slow recovery from the block in the inactivated states. They suggest a common use-dependent block mechanism for hH1a and QQQ involving a high-affinity site. We propose that an activated state is primarily responsible for UDB during short depolarization in the range of the action potential plateau and that fast inactivation modulates the accessibility of the toxin to this site.

scholarly journals Slow Inactivation Does Not Block the Aqueous Accessibility to the Outer Pore of Voltage-gated Na Channels

2002 ◽  
Vol 120 (4) ◽  
pp. 509-516 ◽  
Author(s):  
Arie F. Struyk ◽  
Stephen C. Cannon
Keyword(s):  
Reaction Rates ◽  
Slow Inactivation ◽  
Na Channels ◽  
Fast Inactivation ◽  
Voltage Gated ◽  
State Dependent ◽  
Gating Mechanism ◽  
Dependent Change ◽  
Outer Pore ◽  
Inactivation Gating

Slow inactivation of voltage-gated Na channels is kinetically and structurally distinct from fast inactivation. Whereas structures that participate in fast inactivation are well described and include the cytoplasmic III-IV linker, the nature and location of the slow inactivation gating mechanism remains poorly understood. Several lines of evidence suggest that the pore regions (P-regions) are important contributors to slow inactivation gating. This has led to the proposal that a collapse of the pore impedes Na current during slow inactivation. We sought to determine whether such a slow inactivation-coupled conformational change could be detected in the outer pore. To accomplish this, we used a rapid perfusion technique to measure reaction rates between cysteine-substituted side chains lining the aqueous pore and the charged sulfhydryl-modifying reagent MTS-ET. A pattern of incrementally slower reaction rates was observed at substituted sites at increasing depth in the pore. We found no state-dependent change in modification rates of P-region residues located in all four domains, and thus no change in aqueous accessibility, between slow- and nonslow-inactivated states. In domains I and IV, it was possible to measure modification rates at residues adjacent to the narrow DEKA selectivity filter (Y401C and G1530C), and yet no change was observed in accessibility in either slow- or nonslow-inactivated states. We interpret these results as evidence that the outer mouth of the Na pore remains open while the channel is slow inactivated.

scholarly journals Fast inactivation of Na+ current in rat adrenal chromaffin cells involves two independent inactivation pathways

2020 ◽  
Author(s):  
Pedro L. Martinez-Espinosa ◽  
Alan Neely ◽  
Jiuping Ding ◽  
Christopher J. Lingle
Keyword(s):  
Chromaffin Cells ◽  
Time Course ◽  
Adrenal Chromaffin Cells ◽  
Fast Inactivation ◽  
Fast Recovery ◽  
Slow Recovery ◽  
Recovery Processes ◽  
Voltage Dependent ◽  
Adrenal Chromaffin ◽  
Recovery Pathways

AbstractVoltage-dependent sodium (Nav) current in adrenal chromaffin cells (CCs) is rapidly inactivating and TTX-sensitive. The fractional availability of CC Nav current has been implicated in regulation of action potential (AP) frequency and the occurrence of slow-wave burst firing. To ascertain whether features of CC Nav inactivation might influence AP firing, we recorded Nav current in rat CCs, primarily from adrenal medullary slices. A key feature of CC Nav current is that recovery from inactivation, even following brief (5 ms) inactivation steps, exhibits two exponential components of generally similar amplitude. Variations of standard paired pulse protocols support the view that entry into the fast and slower recovery processes result from largely independent, competing inactivation pathways, both of which occur with similar onset times at depolarizing potentials. Over voltages from −120 to −80 mV, faster recovery varies from ~3 to 30 ms, while slower recovery from about 50-400 ms. At strong activation voltages (+0 mV and more positive), the relative entry into slow or fast recovery pathways is similar and independent of voltage. Trains of brief inactivating steps result in cumulative increases in the slower recovery fraction. This supports idea that brief recovery intervals preferentially allow recovery of channels from fast recovery pathways, thereby increasing the fraction of channels in the slow recovery pathway with each subsequent inactivation step. This provides a mechanism whereby differential rates of recovery produce use-dependent accumulation in slower recovery pathways. Consistent with use-dependent accumulation of channels in slow recovery pathways, repetitive AP clamp waveforms at 1-10 Hz frequencies reduce Nav availability to 10-20% of initial amplitude dependent on holding potential. The results indicate that there are two distinct pathways of fast inactivation, one that leads to normal fast recovery and the other with a slower time course, which together are well-suited to mediate use-dependent changes in Nav availability.

scholarly journals Fast inactivation of Nav current in rat adrenal chromaffin cells involves two independent inactivation pathways

2021 ◽  
Vol 153 (4) ◽  
Author(s):  
Pedro L. Martinez-Espinosa ◽  
Alan Neely ◽  
Jiuping Ding ◽  
Christopher J. Lingle
Keyword(s):  
Chromaffin Cells ◽  
Adrenal Chromaffin Cells ◽  
Fast Inactivation ◽  
Fast Recovery ◽  
Slow Recovery ◽  
Recovery Processes ◽  
Voltage Dependent ◽  
Dual Pathway ◽  
Adrenal Chromaffin ◽  
Recovery Pathways

Voltage-dependent sodium (Nav) current in adrenal chromaffin cells (CCs) is rapidly inactivating and tetrodotoxin (TTX)–sensitive. The fractional availability of CC Nav current has been implicated in regulation of action potential (AP) frequency and the occurrence of slow-wave burst firing. Here, through recordings of Nav current in rat CCs, primarily in adrenal medullary slices, we describe unique inactivation properties of CC Nav inactivation that help define AP firing rates in CCs. The key feature of CC Nav current is that recovery from inactivation, even following brief (5 ms) inactivation steps, exhibits two exponential components of similar amplitude. Various paired pulse protocols show that entry into the fast and slower recovery processes result from largely independent competing inactivation pathways, each of which occurs with similar onset times at depolarizing potentials. Over voltages from −120 to −80 mV, faster recovery varies from ∼3 to 30 ms, while slower recovery varies from ∼50 to 400 ms. With strong depolarization (above −10 mV), the relative entry into slow or fast recovery pathways is similar and independent of voltage. Trains of short depolarizations favor recovery from fast recovery pathways and result in cumulative increases in the slow recovery fraction. Dual-pathway fast inactivation, by promoting use-dependent accumulation in slow recovery pathways, dynamically regulates Nav availability. Consistent with this finding, repetitive AP clamp waveforms at 1–10 Hz frequencies reduce Nav availability 80–90%, depending on holding potential. These results indicate that there are two distinct pathways of fast inactivation, one leading to conventional fast recovery and the other to slower recovery, which together are well-suited to mediate use-dependent changes in Nav availability.

Calcium–calmodulin gating of a pH-insensitive isoform of connexin43 gap junctions

2019 ◽  
Vol 476 (7) ◽  
pp. 1137-1148 ◽  
Author(s):  
Siyu Wei ◽  
Christian Cassara ◽  
Xianming Lin ◽  
Richard D. Veenstra
Keyword(s):  
Gap Junctions ◽  
Ventricular Myocytes ◽  
Protein A ◽  
Ph Sensitivity ◽  
Fast Inactivation ◽  
Inhibitory Peptide ◽  
Pipette Solution ◽  
Calmodulin Binding ◽  
Gap Junction Communication ◽  
Gating Mechanism

Abstract Intracellular protons and calcium ions are two major chemical factors that regulate connexin43 (Cx43) gap junction communication and the synergism or antagonism between pH and Ca2+ has been questioned for decades. To assess the ability of Ca2+ ions to modulate Cx43 junctional conductance (gj) in the absence of pH-sensitivity, patch clamp experiments were performed on Neuroblastoma-2a (N2a) cells or neonatal mouse ventricular myocytes (NMVMs) expressing either full-length Cx43 or the Cx43-M257 (Cx43K258stop) mutant protein, a carboxyl-terminus (CT) truncated version of Cx43 lacking pH-sensitivity. The addition of 1 μM ionomycin to normal calcium saline reduced Cx43 or Cx43-M257 gj to zero within 15 min of perfusion. This response was prevented by Ca2+-free saline or addition of 100 nM calmodulin (CaM) inhibitory peptide to the internal pipette solution. Internal addition of a connexin50 cytoplasmic loop calmodulin-binding domain (CaMBD) mimetic peptide (200 nM) prevented the Ca2+/ionomycin-induced decrease in Cx43 gj, while 100 μM Gap19 peptide had minimal effect. The investigation of the transjunctional voltage (Vj) gating properties of NMVM Cx43-M257 gap junctions confirmed the loss of the fast inactivation of Cx43-M257 gj, but also noted the abolishment of the previously reported facilitated recovery of gj from inactivating potentials. We conclude that the distal CT domain of Cx43 contributes to the Vj-dependent fast inactivation and facilitated recovery of Cx43 gap junctions, but the Ca2+/CaM-dependent gating mechanism remains intact in its absence. Sequence-specific connexin CaMBD mimetic peptides act by binding Ca2+/CaM non-specifically and the Cx43 mimetic Gap19 peptide has negligible effect on this chemical gating mechanism.

scholarly journals Nav1.3 and FGF14 are primary determinants of the TTX-sensitive sodium current in mouse adrenal chromaffin cells

2021 ◽  
Vol 153 (4) ◽  
Author(s):  
Pedro L. Martinez-Espinosa ◽  
Chengtao Yang ◽  
Xiao-Ming Xia ◽  
Christopher J. Lingle
Keyword(s):  
Chromaffin Cells ◽  
Time Course ◽  
Slow Component ◽  
Sodium Current ◽  
Adrenal Chromaffin Cells ◽  
Fast Inactivation ◽  
Slow Recovery ◽  
Recovery From Inactivation ◽  
Adrenal Chromaffin ◽  
Molecular Components

Adrenal chromaffin cells (CCs) in rodents express rapidly inactivating, tetrodotoxin (TTX)-sensitive sodium channels. The resulting current has generally been attributed to Nav1.7, although a possible role for Nav1.3 has also been suggested. Nav channels in rat CCs rapidly inactivate via two independent pathways which differ in their time course of recovery. One subpopulation recovers with time constants similar to traditional fast inactivation and the other ∼10-fold slower, but both pathways can act within a single homogenous population of channels. Here, we use Nav1.3 KO mice to probe the properties and molecular components of Nav current in CCs. We find that the absence of Nav1.3 abolishes all Nav current in about half of CCs examined, while a small, fast inactivating Nav current is still observed in the rest. To probe possible molecular components underlying slow recovery from inactivation, we used mice null for fibroblast growth factor homology factor 14 (FGF14). In these cells, the slow component of recovery from fast inactivation is completely absent in most CCs, with no change in the time constant of fast recovery. The use dependence of Nav current reduction during trains of stimuli in WT cells is completely abolished in FGF14 KO mice, directly demonstrating a role for slow recovery from inactivation in determining Nav current availability. Our results indicate that FGF14-mediated inactivation is the major determinant defining use-dependent changes in Nav availability in CCs. These results establish that Nav1.3, like other Nav isoforms, can also partner with FGF subunits, strongly regulating Nav channel function.

Sustainable Development Through Innovation In Service Sector

2014 ◽  
Vol 1 (1) ◽  
pp. 175-178
Author(s):  
Ilie Banu ◽  
Ioana Madalina Butiuc
Keyword(s):  
Sustainable Development ◽  
Tax Evasion ◽  
Service Sector ◽  
Service Innovation ◽  
Slow Recovery ◽  
Quality Research ◽  
Development Indicators ◽  
Economic Cycles ◽  
Sustainable Development Indicators ◽  
Research And Innovation

AbstractRegarding the economic crises and the slow recovery that still continues, we believe that a solution can be improving the capacity to research and innovate in order to achieve sustainable development. Another key issue of the paper is about developing the cooperation between academia and business. The challenge of this development is how to increase the amount to finance research and innovation that can be implemented in the economy. As a global solution, to this problem we can recommend, for example, reducing tax evasion and by fiscal education. Also particular sources have to be found in order to develop innovation on SME level. It is essential for innovation to make quality research in order to be better prepared and increase adaptability to economic cycles. The aim of the paper is to find out how service innovation and cooperation between academia and business can enhance sustainable development indicators. The conclusions of the paper are structured in particular proposals and recommendations.

Evidence for a single mechanism gating perceptual and long-term memory information into working memory

2020 ◽  
Author(s):  
Sam Verschooren ◽  
Yoav Kessler ◽  
Tobias Egner
Keyword(s):  
Working Memory ◽  
Long Term Memory ◽  
Sources Of Information ◽  
Term Memory ◽  
Source Selection ◽  
Single Mechanism ◽  
Gating Mechanism ◽  
Opening And Closing ◽  
Selection Of

An influential view of working memory (WM) holds that its’ contents are controlled by a selective gating mechanism that allows for relevant perceptual information to enter WM when opened, but shields WM contents from interference when closed. In support of this idea, prior studies using the reference-back paradigm have established behavioral costs for opening and closing the gate between perception and WM. WM also frequently requires input from long-term memory (LTM), but it is currently unknown whether a similar gate controls the selection of LTM representations into WM, and how WM gating of perceptual vs. LTM sources of information relate to each other. To address these key theoretical questions, we devised a novel version of the reference-back paradigm, where participants switched between gating perceptual and LTM information into WM. We observed clear evidence for gate opening and closing costs in both cases. Moreover, the pattern of costs associated with gating and source-switching indicated that perceptual and LTM information is gated into WM via a single gate, and rely on a shared source-selection mechanism. These findings extend current models of WM gating to encompass LTM information, and outline a new functional WM architecture.

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