Ion Channel Desensitization Research Articles

The role of melatonin in regulating horticultural crop production under various abiotic stresses

Horticultural crops are very important component of our food chain, and their production is highly sensitive to different soil related abiotic stresses (SRAS). These stresses reduce plant growth and development by reducing seed germination (SG), seedling establishment, photosynthesis, reproduction, thus reduce fruit yield and quality. Nonetheless application of plant growth regulators has been shown a very promising technique to confer SRAS tolerance in horticultural crops. Melatonin (Mel)-a high conserved and stress regulatory molecule regulates a plethora of stress adaptive responses in plants. This paper summarizes the current state of knowledge of Mel involvement in regulating stress adaptive responses under SRAS. The major topic covered in this review included: (i) the effects of exogenous Mel application on seed germination, photosynthesis, flowering, and fruit yield under different SRAS, (ii) Mel crosstalk with stress regulatory mechanism to confer stress tolerance in horticultural crops. Latter topic further discussed the role of Mel in regulating (i) redox regulation, (ii) ionic homeostasis, and (iii) hormonal regulation. We show that Mel regulates stress adaptive responses and improves plant growth by allowing the direct scavenging of ROS, up-regulation of H+-ATPase activity and vacuolar sequestration of toxic ions in cytosol and activation of ROS-Ca2+ hub, which latter prevent the negative effects of ROS and membrane depolarization on the ROS-activated and voltage-activated ion channels. Such Mel mediated desensitization of ion channels may play a crucial role in reducing stress induced efflux of mineral ions such as K, Zn, Mg from cytosol, thereby improving plant growth. Moreover, Mel may operate in tandem with polyamines to regulate the biosynthesis of different phytohormones. However, studies are required to reveal the molecular identity of genes relating to Mel-polyamine tandem and to light signaling that could directly regulate phytohormone biosynthesis and the interaction of Mel with light signaling in regulating SG.

β11-12 linker isomerization governs acid-sensing ion channel desensitization and recovery.

Acid-sensing ion channels (ASICs) are neuronal sodium-selective channels activated by reductions in extracellular pH. Structures of the three presumptive functional states, high-pH resting, low-pH desensitized, and toxin-stabilized open, have all been solved for chicken ASIC1. These structures, along with prior functional data, suggest that the isomerization or flipping of the β11-12 linker in the extracellular, ligand-binding domain is an integral component of the desensitization process. To test this, we combined fast perfusion electrophysiology, molecular dynamics simulations and state-dependent non-canonical amino acid cross-linking. We find that both desensitization and recovery can be accelerated by orders of magnitude by mutating resides in this linker or the surrounding region. Furthermore, desensitization can be suppressed by trapping the linker in the resting state, indicating that isomerization of the β11-12 linker is not merely a consequence of, but a necessity for the desensitization process in ASICs.

Melting Away Pain: Decay of Thermal Nociceptor Transduction during Heat-Induced Irreversible Desensitization of Ion Channels

Thermal transient receptor potential channels play a key role in thermal sensation. Although predictive models exist for temperature-dependent transduction through these channels and for the associated sensations of pain, the ability to predict irreversible desensitization has been lacking. We explored the role of irreversible ion channel desensitization in pain sensation and hypothesized that desensitization of ion channels would follow the kinetics similar to the denaturation of catalytic enzymes. We therefore proposed a three-state model to simulate the kinetic of temperature-sensitive ion channels from the closed state through opening and irreversible thermal desensitization. We tested the model against data obtained in vivo from a feline model. The theoretical model predicts all experimental data with reasonable accuracy, and represents an important step toward the ability for understanding of the molecular basis of nociceptor signaling providing the possibility to design local anesthesia regimens and to the prediction of postoperative pain.

The Thumb Domain Mediates Acid-sensing Ion Channel Desensitization

Acid-sensing ion channels (ASICs) are cation-selective proton-gated channels expressed in neurons that participate in diverse physiological processes, including nociception, synaptic plasticity, learning, and memory. ASIC subunits contain intracellular N and C termini, two transmembrane domains that constitute the pore, and a large extracellular loop with defined domains termed the finger, β-ball, thumb, palm, and knuckle. Here we examined the contribution of the finger, β-ball, and thumb domains to activation and desensitization through the analysis of chimeras and the assessment of the effect of covalent modification of introduced Cys at the domain-domain interfaces. Our studies with ASIC1a-ASIC2a chimeras showed that swapping the thumb domain between subunits results in faster channel desensitization. Likewise, the covalent modification of Cys residues at selected positions in the β-ball-thumb interface accelerates the desensitization of the mutant channels. Studies of accessibility with thiol-reactive reagents revealed that the β-ball and thumb domains reside apart in the resting state but that they become closer to each other in response to extracellular acidification. We propose that the thumb domain moves upon continuous exposure to an acidic extracellular milieu, assisting with the closing of the pore during channel desensitization.

Characteristics of the Desensitization of Glycine-Mediated Ion Currents in Frog Spinal Cord Neurons

Whole-cell patch clamp studies of isolated spinal cord neurons from the frog Rana temporaria in voltage-clamped conditions addressed the kinetics of ion channel desensitization evoked by glycine application. The ion current desensitization phase (decay from 90% to 10%), induced by periodic applications of glycine (1 mM), approximated an exponential function. Approximation results identified three types of glycine-mediated response. The decay constant of type 1 responses in the first minute of the experiment was τ1 = 1693 ± 135 msec (n = 8) and decreased from application to application during further recording. Type 2 responses had a decay constant τ2 = 364 ± 42 msec (n = 9) at the beginning of recording and showed virtually no change with time. Type 3 responses had a biexponential decay consisting of a rapid (τ2) component and a slow (τ1) component, acceleration of the desensitization phase of this response from application to application occurring as a result of a decrease in the larger decay constant τ1. These data suggest that the frog spinal cord membrane has at least two varieties of glycine receptor with different rates of desensitization and different dynamics of changes in properties during patch-clamp recording. Different neurons can evidently have these receptor varieties simultaneously or separately.

Point-to-point ligand–receptor interactions across the subunit interface modulate the induction and stabilization of conformational states of alpha7 nAChR by benzylidene anabaseines

The homomeric α7 nicotinic acetylcholine receptor is a well-studied therapeutic target, though its characteristically rapid desensitization complicates the development of drugs with specific agonist effects. Moreover, some experimental compounds such as GTS-21 (2,4diMeOBA), a derivative of the α7-selective partial agonist benzylidene anabaseine (BA), produce a prolonged residual desensitization (RD) in which the receptor remains non-activatable long after the drug has been removed from extracellular solution. In contrast, the desensitization caused by GTS-21's dihydroxy metabolite (2,4diOHBA) is relatively short-lived. RD is hypothetically due to stable binding of the ligand to the receptor in its desensitized state. We can attribute the reduction in RD to a single BA hydroxyl group on the 4′ benzylidene position. Computational prediction derived from homology modeling showed the serine36 (S36) residue of α7 as a reasonable candidate for point-to-point interaction between BA compounds and the receptor. Through evaluating the activity of BA and simple derivatives on wild-type and mutant α7 receptors, it was observed that the drug–receptor pairs which were capable of hydrogen bonding at residue 36 exhibited significantly less stable desensitization. Further experiments involving the type II positive allosteric modulator (PAM) PNU-120596 showed that the various BA compounds’ preference to induce either a PAM-sensitive (Ds) or PAM-insensitive (Di) desensitized state is concentration dependent and suggested that both states are destabilized by S36 H-bonding. These results indicate that the fine-tuning of agonists for specific interaction with S36 can facilitate the development of therapeutics with targeted effects on ion channel desensitization properties and conformational state stability.

Novel Regulatory Site within the TM3–4 Loop of Human Recombinant α3 Glycine Receptors Determines Channel Gating and Domain Structure

Glycine receptors are Cys loop ligand-gated ion channels that mediate fast inhibitory synaptic transmission in the mammalian central nervous system. The functionally distinct splice variants alpha3L and alpha3K of the human glycine receptor differ by a 15-amino acid insert within the long intracellular TM3-4 loop, a region of high intersubunit diversity. In a mutational study, effects of the insert on ion channel function and secondary structure of the TM3-4 loop were investigated. Whole cell current responses and protein surface expression data indicated that the major effect of mutations within the insert was on channel gating. Changes in channel gating correlated with the distribution of charged residues about the splice region. Analysis of complex molecular weight indicated that recombinant TM3-4 loops of alpha3L and alpha3K associated into oligomers of different stoichiometry. Secondary structure analysis suggested that the insert stabilized the overall fold of the large cytoplasmic domain of alpha3L subunits. The absence of the insert resulted in a channel that was still functional, but the TM3-4 cytoplasmic domain appeared not stably folded. Thus, our data identified the spliced insert within the large TM 3-4 loop of alpha3 Gly receptors as a novel regulatory motif that serves a 2-fold role: (i) the presence of the insert stabilizes the overall spatial structure of the domain, and (ii) the insert presents a control unit that regulates gating of the receptor ion channel.

Research Profile: Controlling ion-channel desensitization

ADVERTISEMENT RETURN TO ISSUEPREVNEWSNEXTResearch Profile: Controlling ion-channel desensitizationRajendrani MukhopadhyayCite this: Anal. Chem. 2006, 78, 23, 7911Publication Date (Web):December 1, 2006Publication History Published online1 December 2006Published inissue 1 December 2006https://doi.org/10.1021/ac069500mRIGHTS & PERMISSIONSArticle Views701Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (51 KB) Get e-Alerts Get e-Alerts

Use of the Covariance Matrix in Directly Fitting Kinetic Parameters: Application to GABA A Receptors

A new method of analysis is described that begins to explore the relationship between the phases of ion channel desensitization and the underlying states of the channel. The method, referred to as covariance fitting (CVF), couples Q-matrix calculations with a maximum likelihood algorithm to fit macroscopic desensitization data directly to kinetic models. Unlike conventional sum-of-squares minimization, CVF fits both the magnitude of the recorded current and the strength of the correlations between different time points. When applied to simulated data generated using various kinetic models with up to 11 free parameters, CVF leads to reasonable parameter estimates. Coupled with the likelihood ratio test, it accurately discriminates between models with different numbers of states, discriminates between most models with the same number but a different arrangement of states, and extracts meaningful information on the relationship between the desensitized states and the phases of macroscopic desensitization. When applied to GABA A receptor traces (outside out patches, α1 β2 γ2S, 1 mM GABA, >2.5 s), a model with two open states and three desensitized states is favored. When applied to simulated data generated using a consensus model, CVF leads to reasonable parameter estimates and accurately discriminates between this and other models.