Kinetics of calcium channel opening by inositol 1,4,5-trisphosphate

Biochemistry ◽  
1990 ◽  
Vol 29 (1) ◽  
pp. 32-37 ◽  
Author(s):  
Tobias Meyer ◽  
Theodore Wensel ◽  
Lubert Stryer
Keyword(s):  
Calcium Channel ◽  
Channel Opening ◽  
Inositol 1,4,5 Trisphosphate ◽  
Kinetics Of

scholarly journals Desensitization Contributes to the Synaptic Response of Gain-of-Function Mutants of the Muscle Nicotinic Receptor

2006 ◽  
Vol 128 (5) ◽  
pp. 615-627 ◽  
Author(s):  
Sergio Elenes ◽  
Ying Ni ◽  
Gisela D. Cymes ◽  
Claudio Grosman
Keyword(s):  
Nicotinic Receptor ◽  
Dissociation Rate ◽  
Gain Of Function ◽  
Naturally Occurring ◽  
Channel Opening ◽  
Speed Up ◽  
High Concentrations ◽  
Dissociation Rate Constants ◽  
Kinetics Of ◽  
Peak Value

Although the muscle nicotinic receptor (AChR) desensitizes almost completely in the steady presence of high concentrations of acetylcholine (ACh), it is well established that AChRs do not accumulate in desensitized states under normal physiological conditions of neurotransmitter release and clearance. Quantitative considerations in the framework of plausible kinetic schemes, however, lead us to predict that mutations that speed up channel opening, slow down channel closure, and/or slow down the dissociation of neurotransmitter (i.e., gain-of-function mutations) increase the extent to which AChRs desensitize upon ACh removal. In this paper, we confirm this prediction by applying high-frequency trains of brief (∼1 ms) ACh pulses to outside-out membrane patches expressing either lab-engineered or naturally occurring (disease-causing) gain-of-function mutants. Entry into desensitization was evident in our experiments as a frequency-dependent depression in the peak value of succesive macroscopic current responses, in a manner that is remarkably consistent with the theoretical expectation. We conclude that the comparatively small depression of the macroscopic currents observed upon repetitive stimulation of the wild-type AChR is due, not to desensitization being exceedingly slow but, rather, to the particular balance between gating, entry into desensitization, and ACh dissociation rate constants. Disruption of this fine balance by, for example, mutations can lead to enhanced desensitization even if the kinetics of entry into, and recovery from, desensitization themselves are not affected. It follows that accounting for the (usually overlooked) desensitization phenomenon is essential for the correct interpretation of mutagenesis-driven structure–function relationships and for the understanding of pathological synaptic transmission at the vertebrate neuromuscular junction.

Desensitization and resensitization rates of glutamate-activated channels may regulate motoneuron excitability

1991 ◽  
Vol 66 (4) ◽  
pp. 1166-1175 ◽  
Author(s):  
D. O. Smith ◽  
C. Franke ◽  
J. L. Rosenheimer ◽  
F. Zufall ◽  
H. Hatt
Keyword(s):  
Ampa Receptors ◽  
Single Channel ◽  
Kainate Receptors ◽  
Whole Cell ◽  
Solution Exchange ◽  
Channel Opening ◽  
Fast Solution ◽  
Agonist Concentration ◽  
Kinetics Of ◽  
Channel Properties

1. Single-channel properties of desensitizing glutamate-activated channels were analyzed in outside-out patch-clamp recordings from a motoneuron-enriched cell fraction from embryonic chick. A piezo-driven device was used to achieve fast solution exchange at the electrode tip, resulting in maximum activation within 2 ms. 2. Quisqualate/AMPA receptors, with a 13-pS conductance, desensitized rapidly; the desensitization rate depended on agonist concentration but not on membrane potential. When quisqualate was applied slowly, the quisqualate-activated channels desensitized without prior channel opening, indicating desensitization from the closed state. After a 10-ms refractory period, resensitization of all channels required up to 300 ms; resensitization rate did not depend on the duration of the preceding quisqualate application. 3. At agonist concentrations less than or equal to 1 mM, kainate receptors, with a 20-pS conductance, did not desensitize. At kainate concentrations greater than or equal to 1 mM, though, kainate receptors desensitized to a low steady-state conductance within approximately 200 ms. Resensitization of all channels required as long as 3 s, which could render kainate receptors inexcitable during high-frequency activation. 4. Desensitization rates of whole-cell currents were similar to those observed in outside-out mode. Glutamate- and quisqualate-activated responses were similar, suggesting that the rapidly desensitizing quisqualate-sensitive receptor type may dominate the kinetics of whole-cell excitatory postsynaptic currents (EPSCs) in this preparation. 5. It may be concluded that the efficacy of glutamate-mediated synaptic transmission is modulated by differences in the rates of desensitization and resensitization.

scholarly journals Effect of adenine nucleotides on myo-inositol-1,4,5-trisphosphate-induced calcium release

1997 ◽  
Vol 325 (3) ◽  
pp. 661-666 ◽  
Author(s):  
Ludwig MISSIAEN ◽  
Jan B. PARYS ◽  
Humbert DE SMEDT ◽  
Ilse SIENAERT ◽  
Henk SIPMA ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Binding Site ◽  
Calcium Release ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Release Process ◽  
A7r5 Cells ◽  
Channel Opening ◽  
Inositol 1,4,5 Trisphosphate

The effects of a whole series of adenine nucleotides on Ins(1,4,5)P3-induced Ca2+ release were characterized in permeabilized A7r5 smooth-muscle cells. Several adenine nucleotides activated the Ins(1,4,5)P3 receptor. It was observed that 3′-phosphoadenosine 5′-phosphosulphate, CoA, di(adenosine-5′)tetraphosphate (Ap4A) and di(adenosine-5′)pentaphosphate (Ap5A) were more effective than ATP. Ap4A and Ap5A also interacted with a lower EC50 than ATP. In order to find out how these adenine nucleotides affected Ins(1,4,5)P3-induced Ca2+ release, we have measured their effect on the response of permeabilized A7r5 cells to a progressively increasing Ins(1,4,5)P3 concentration. Stimulatory ATP and Ap5A concentrations had no effect on the threshold Ins(1,4,5)P3 concentration for initiating Ca2+ release, but they stimulated Ca2+ release in the presence of supra-threshold Ins(1,4,5)P3 concentrations by increasing the co-operativity of the release process. Inhibition of the Ins(1,4,5)P3-induced Ca2+ release at higher ATP concentrations was associated with a further increase in co-operativity and also with a shift in threshold towards higher Ins(1,4,5)P3 concentrations. ATP had no effect on the non-specific Ca2+ leak in the absence of Ins(1,4,5)P3. We conclude that the adenine-nucleotide-binding site can be activated by many different adenine nucleotides. Binding of these compounds to the transducing domain of the Ins(1,4,5)P3 receptor increases the efficiency of transmitting Ins(1,4,5)P3 binding to channel opening. The inhibition by high ATP concentrations is exerted at a different site, related to Ins(1,4,5)P3 binding.

scholarly journals Evolutionary divergence reveals the molecular basis of EMRE dependence of the human MCU

2020 ◽  
Vol 3 (10) ◽  
pp. e202000718 ◽  
Author(s):  
Melissa JS MacEwen ◽  
Andrew L Markhard ◽  
Mert Bozbeyoglu ◽  
Forrest Bradford ◽  
Olga Goldberger ◽  
...  
Keyword(s):  
Calcium Channel ◽  
Molecular Basis ◽  
Homo Sapiens ◽  
Transmembrane Domains ◽  
Chimeric Proteins ◽  
Evolutionary Divergence ◽  
Mitochondrial Calcium Uniporter ◽  
Calcium Uniporter ◽  
Channel Opening ◽  
Strict Requirement

The mitochondrial calcium uniporter (MCU) is a calcium-activated calcium channel critical for signaling and bioenergetics. MCU, the pore-forming subunit of the uniporter, contains two transmembrane domains and is found in all major eukaryotic taxa. In amoeba and fungi, MCU homologs are sufficient to form a functional calcium channel, whereas human MCU exhibits a strict requirement for the metazoan protein essential MCU regulator (EMRE) for conductance. Here, we exploit this evolutionary divergence to decipher the molecular basis of human MCU’s dependence on EMRE. By systematically generating chimeric proteins that consist of EMRE-independent Dictyostelium discoideum MCU and Homo sapiens MCU (HsMCU), we converged on a stretch of 10 amino acids in D. discoideum MCU that can be transplanted to HsMCU to render it EMRE independent. We call this region in human MCU the EMRE dependence domain (EDD). Crosslinking experiments show that EMRE directly interacts with HsMCU at its transmembrane domains as well as the EDD. Our results suggest that EMRE stabilizes the EDD of MCU, permitting both channel opening and calcium conductance, consistent with recently published structures of MCU-EMRE.

scholarly journals Suppression of mICAT in Mouse Small Intestinal Myocytes by General Anaesthetic Ketamine and its Recovery by TRPC4 Agonist (-)-englerin A

2020 ◽  
Vol 11 ◽  
Author(s):  
Mariia I. Melnyk ◽  
Dariia O. Dryn ◽  
Lina T. Al Kury ◽  
Dmytro O. Dziuba ◽  
Alexander V. Zholos
Keyword(s):  
Negative Impact ◽  
Receptor Activation ◽  
General Anaesthetic ◽  
General Anesthetics ◽  
Englerin A ◽  
Cationic Current ◽  
Channel Opening ◽  
Trpc4 Channel ◽  
Novel Target ◽  
Kinetics Of

A better understanding of the negative impact of general anesthetics on gastrointestinal motility requires thorough knowledge of their molecular targets. In this respect the muscarinic cationic current (mICAT carried mainly via TRPC4 channels) that initiates cholinergic excitation-contraction coupling in the gut is of special interest. Here we aimed to characterize the effects of one of the most commonly used “dissociative anesthetics”, ketamine, on mICAT. Patch-clamp and tensiometry techniques were used to investigate the mechanisms of the inhibitory effects of ketamine on mICAT in single mouse ileal myocytes, as well as on intestinal motility. Ketamine (100 µM) strongly inhibited both carbachol- and GTPγS-induced mICAT. The inhibition was slow (time constant of about 1 min) and practically irreversible. It was associated with altered voltage dependence and kinetics of mICAT. In functional tests, ketamine suppressed both spontaneous and carbachol-induced contractions of small intestine. Importantly, inhibited by ketamine mICAT could be restored by direct TRPC4 agonist (-)-englerin A. We identified mICAT as a novel target for ketamine. Signal transduction leading to TRPC4 channel opening is disrupted by ketamine mainly downstream of muscarinic receptor activation, but does not involve TRPC4 per se. Direct TRPC4 agonists may be used for the correction of gastrointestinal disorders provoked by general anesthesia.

Luminal calcium regulation of calcium release from sarcoplasmic reticulum

1995 ◽  
Vol 15 (5) ◽  
pp. 387-397 ◽  
Author(s):  
Cecilia Hidalgo ◽  
Paulina Donoso
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Concentration ◽  
Calcium Release ◽  
Single Channel ◽  
Release Rates ◽  
Calcium Release Channels ◽  
Channel Opening ◽  
Inositol 1,4,5 Trisphosphate ◽  
Luminal Calcium ◽  
Trisphosphate Receptor

This article discusses how changes in luminal calcium concentration affect calcium release rates from triad-enriched sarcoplasmic reticulum vesicles, as well as single channel opening probability of the ryanodine receptor/calcium release channels incorporated in bilayers. The possible participation of calsequestrin, or of other luminal proteins of sarcoplasmic reticulum in this regulation is addressed. A comparison with the regulation by luminal calcium of calcium release mediated by the inositol 1,4,5-trisphosphate receptor/calcium channel is presented as well.

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