Isoflurane and Sevoflurane Interact with the Nicotinic Acetylcholine Receptor Channels in Micromolar Cconcentrations

1997 ◽  
Vol 86 (1) ◽  
pp. 118-127 ◽  
Author(s):  
Michaela Scheller ◽  
Johannes Bufler ◽  
Hajo Schneck ◽  
Eberhard Kochs ◽  
Christian Franke
Keyword(s):  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Nicotinic Acetylcholine ◽  
Current Decay ◽  
Low Concentrations ◽  
Time Courses ◽  
Clinical Anesthesia

Background This study was performed to elucidate and compare the effects of sevoflurane and of isoflurane on the nicotinic acetylcholine receptor of mouse myotubes. The experiments were done with special reference to anesthetic concentrations considerably less than those used for clinical anesthesia. Methods The patch-clamp technique was used to record acetylcholine-activated currents from the embryonic type of the nicotinic acetylcholine receptor in the outside-out mode. A piezo-driven liquid filament switch was used for the ultrafast application of acetylcholine alone or in combination with isoflurane or sevoflurane. In addition, the patches were preexposed to either anesthetic, preceding the activation with acetylcholine. Results The current elicited by acetylcholine was reduced reversibly and in a concentration-dependent manner by both anesthetics, which were equally effective. Preexposure of the patches to isoflurane or sevoflurane showed an additional inhibition that was present at micromolar concentrations. The time courses of current decay could be fitted by single exponentials for isoflurane. At higher concentrations of sevoflurane, the current decay became biexponential. In contrast to isoflurane, sevoflurane increased the time constants of desensitization when applied in low concentrations. Conclusions At the nicotinic acetylcholine receptor, isoflurane and sevoflurane act primarily through the same mechanisms: Both affect the open and the closed state of the channels in concentrations equal to and less than those encountered clinically. The kinetics of desensitization, however, are altered in a different manner. Thus there may be several different sites of interaction.

scholarly journals Mechanism of calcium potentiation of the α7 nicotinic acetylcholine receptor

2020 ◽  
Vol 152 (9) ◽  
Author(s):  
Kathiresan Natarajan ◽  
Nuriya Mukhtasimova ◽  
Jeremías Corradi ◽  
Matías Lasala ◽  
Cecilia Bouzat ◽  
...  
Keyword(s):  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Single Channel ◽  
Structural Motif ◽  
Site Mutation ◽  
Α7 Nicotinic Acetylcholine Receptor ◽  
Nicotinic Acetylcholine ◽  
Low Concentrations ◽  
Channel Opening ◽  
Dynamics Simulations

The α7 nicotinic acetylcholine receptor (nAChR) is among the most abundant types of nAChR in the brain, yet the ability of nerve-released ACh to activate α7 remains enigmatic. In particular, a major population of α7 resides in extra-synaptic regions where the ACh concentration is reduced, owing to dilution and enzymatic hydrolysis, yet ACh shows low potency in activating α7. Using high-resolution single-channel recording techniques, we show that extracellular calcium is a powerful potentiator of α7 activated by low concentrations of ACh. Potentiation manifests as robust increases in the frequency of channel opening and the average duration of the openings. Molecular dynamics simulations reveal that calcium binds to the periphery of the five ligand binding sites and is framed by a pair of anionic residues from the principal and complementary faces of each site. Mutation of residues identified by simulation prevents calcium from potentiating ACh-elicited channel opening. An anionic residue is conserved at each of the identified positions in all vertebrate species of α7. Thus, calcium associates with a novel structural motif on α7 and is an obligate cofactor in regions of limited ACh concentration.

Immunoenzymometric assay and radioimmunoassay measure different populations of antibody against human acetylcholine receptor.

1985 ◽  
Vol 31 (6) ◽  
pp. 835-840 ◽  
Author(s):  
C L Hinman ◽  
C M Kellogg ◽  
R M Ernstoff ◽  
H C Rauch ◽  
R A Hudson
Keyword(s):  
Myasthenia Gravis ◽  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Nicotinic Acetylcholine ◽  
Receptor Antibody ◽  
Low Concentrations ◽  
Sandwich Type ◽  
Different Populations ◽  
Receptor Antibodies

Abstract We used a "sandwich"-type immunoenzymometric assay (IEMA) and a radioimmunoassay (RIA) to measure antibody against the human nicotinic acetylcholine receptor in serum from individuals with myasthenia gravis, with markedly different results for certain specimens, as measured by the two techniques. In some cases, antibody concentrations were high by RIA but low by IEMA; in others, the reverse was found. Such differences persisted through 30 months after thymectomy. An investigation of potential causes of this disparity suggests that high IEMA measurements reflect specific anti-receptor antibody and are not artifactual. The IEMA is recommended as an adjunct to the RIA because some patients with myasthenia gravis who have low concentrations of anti-receptor antibodies as measured by RIA have significantly above-normal concentrations of anti-receptor antibodies as measured by IEMA.

scholarly journals Assembly intermediates of the mouse muscle nicotinic acetylcholine receptor in stably transfected fibroblasts.

1990 ◽  
Vol 111 (6) ◽  
pp. 2601-2611 ◽  
Author(s):  
P Blount ◽  
M M Smith ◽  
J P Merlie
Keyword(s):  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Lectin Binding ◽  
Dependent Manner ◽  
Nicotinic Acetylcholine ◽  
Mouse Muscle ◽  
A Value ◽  
Sds Page ◽  
The Stability ◽  
Alpha Bungarotoxin

We have used fibroblast clones expressing muscle nicotinic acetylcholine receptor alpha and gamma, and alpha and delta subunits to measure the kinetics of subunit assembly, and to study the properties of the partially assembled products that are formed. We demonstrate by coimmunoprecipitation that assembly intermediates in fibroblasts coexpressing alpha and delta subunits are formed in a time-dependent manner. The alpha and gamma- and the alpha and delta-producing transfected cells form complexes that, when labeled with 125I-alpha-bungarotoxin, migrate in sucrose gradients at 6.3S, a value consistent with a hetero-dimer structure. An additional peak at 8.5S is formed from the alpha and gamma subunits expressed in fibroblasts suggesting that gamma may have more than one binding site for alpha subunit. The stability and specificity of formation of these partially assembled complexes suggests that they are normal intermediates in the assembly of acetylcholine receptor. Comparison of the binding of 125I-alpha-bungarotoxin to intact and detergent-extracted fibroblasts indicate that essentially all of the binding sites are retained in an intracellular pool. The fibroblast delta subunit has the electrophoretic mobility in SDS-PAGE of a precursor that does not contain complex carbohydrates. In addition, alpha gamma and alpha delta complexes had lectin binding properties expected of subunits lacking complex oligosaccharides. Therefore, fibroblasts coexpressing alpha and gamma or alpha and delta subunits produce discrete assembly intermediates that are retained in an intracellular compartment and are not processed by Golgi enzymes.

A Non-α7 Nicotinic Acetylcholine Receptor Modulates Excitatory Input to Hippocampal CA1 Interneurons

2002 ◽  
Vol 87 (3) ◽  
pp. 1651-1654 ◽  
Author(s):  
Manickavasagom Alkondon ◽  
Edson X. Albuquerque
Keyword(s):  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Hippocampal Slices ◽  
Brain Regions ◽  
Excitatory Input ◽  
Stratum Radiatum ◽  
Patch Clamp Technique ◽  
Α7 Nicotinic Acetylcholine Receptor ◽  
Nicotinic Acetylcholine ◽  
Α7 Nachr

The nicotinic acetylcholine receptor (nAChR), particularly the α7 subtype, has received profound attention for its role in modifying excitatory postsynaptic currents (EPSCs) in hippocampal pyramidal neurons as well as in neurons from other brain regions. Here, we tested the possibility that an nAChR could affect EPSCs in the interneurons of rat hippocampal slices. Using whole-cell patch-clamp technique on CA1 stratum radiatum interneurons and U-tube application of agents, we show that nicotinic agonists enhance EPSC frequency in interneurons. Among the agents tested, cytisine and mecamylamine were the most effective agonist and antagonist, respectively, suggesting a role for α3β4-containing nAChRs in the modulation of interneuron EPSCs. Ligands selective for the α7 nAChR had very little or no effect on interneuron EPSCs. Low concentrations of nicotine also enhanced EPSC frequency, implicating the involvement of non-α7 nAChRs in controlling interneuron excitability in smokers. We conclude that nAChR-dependent EPSC modulation in the hippocampus is both subtype- and neuron-specific and that a non-α7 nAChR, presumably α3β4, controls glutamate transmission to CA1 interneurons.

Neutrophil Elastase Potentiates Cathepsin G-lnduced Platelet Activation

1992 ◽  
Vol 68 (05) ◽  
pp. 570-576 ◽  
Author(s):  
Mary A Selak
Keyword(s):  
Neutrophil Elastase ◽  
Cell Activation ◽  
Thromboxane A2 ◽  
Creatine Phosphate ◽  
Dense Granule ◽  
Cathepsin G ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Low Concentrations ◽  
High Concentrations

SummaryWe have previously demonstrated that human neutrophil cathepsin G is a strong platelet agonist that binds to a specific receptor. This work describes the effect of neutrophil elastase on cathepsin G-induced platelet responses. While platelets were not activated by high concentrations of neutrophil elastase by itself, elastase enhanced aggregation, secretion and calcium mobilization induced by low concentrations of cathepsin G. Platelet aggregation and secretion were potentiated in a concentration-dependent manner by neutrophil elastase with maximal responses observable at 200 nM. Enhancement was observed when elastase was preincubated with platelets for time intervals of 10–60 s prior to addition of a low concentration of cathepsin G and required catalytically-active elastase since phenylmethanesulphonyl fluoride-inhibited enzyme failed to potentiate cell activation. Neutrophil elastase potentiation of platelet responses induced by low concentrations of cathepsin G was markedly inhibited by creatine phosphate/creatine phosphokinase and/or indomethacin, indicating that the synergism between elastase and cathepsin G required the participation of ADP and thromboxane A2. On the other hand, platelet responses were not attenuated by the PAF antagonist BN 52021, signifying that PAF-acether did not play a role in elastase potentiation. At higher concentrations porcine pancreatic elastase exhibits similar effects to neutrophil elastase, demonstrating that the effect of elastase was not unique to the neutrophil protease. While neutrophil elastase failed to alter the ability of cathepsin G to hydrolyze a synthetic chromogenic substrate, preincubation of platelets with elastase increased the apparent affinity of cathepsin G binding to platelets. In contrast to their effect on cathepsin G-induced platelet responses, neither neutrophil nor pancreatic elasatse potentiated aggregation or dense granule release initiated by ADP, PAF-acether, arachidonic acid or U46619, a thromboxane A2 mimetic. Moreover, unlike its effect on cathepsin G, neutrophil elastase inhibited thrombin-induced responses. The current observations demonstrate that elastase can potentiate platelet responses mediated by low concentrations of cathepsin G, suggesting that both enzymes may function synergistically to activate platelets under conditions where neutrophil degranulation occurs.

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