Neurotransmitter Modulation of Neuronal Calcium Channels

There are many different calcium channels expressed in the mammalian nervous system, but N-type and P/Q-type calcium channels appear to dominate the presynaptic terminals of central and peripheral neurons. The neurotransmitter-induced modulation of these channels can result in alteration of synaptic transmission. This review highlights the mechanisms by which neurotransmitters affect the activity of N-type and P/Q-type calcium channels. The inhibition of these channels by voltage-dependent and voltage-independent mechanisms is emphasized because of the wealth of information available on the intracellular mediators and on the effect of these pathways on the single-channel gating.     

Modulation of Neuronal Voltage-Activated Calcium and Sodium Channels by Polyamines and pH

The endogenous polyamines spermine, spermidine and putrescine are present at high concentrations inside neurons and can be released into the extracellular space where they have been shown to modulate ion channels. Here, we have examined polyamine modulation of voltage-activated Ca2+ channels (VACCs) and voltage-activated Na+ channels (VANCs) in rat superior cervical ganglion neurons using whole-cell voltage-clamp at physiological divalent concentrations. Polyamines inhibited VACCs in a concentration-dependent manner with IC50s for spermine, spermidine, and putrescine of 4.7 ± 0.7, 11.2 ± 1.4, and 90 ± 36 mM, respectively. Polyamines caused inhibition by shifting the VACC half-activation voltage (V0.5) to depolarized potentials and by reducing total VACC permeability. The shift was described by Gouy-Chapman-Stern theory with a surface charge density of 0.120 ± 0.005 e- nm-2 and a surface potential of -19 mV. Attenuation of spermidine and spermine inhibition of VACC at decreased pH was explained by H+ titration of surface charge. Polyamine-mediated effects also decreased at elevated pH due to the inhibitors having lower valence and being less effective at screening surface charge. Polyamines affected VANC currents indirectly by reducing TTX inhibition of VANCs at high pH. This may reflect surface charge induced decreases in the local TTX concentration or polyamine-TTX interactions. In conclusion, polyamines inhibit neuronal VACCs via complex interactions with extracellular H+ and Ca. Many of the observed effects can be explained by a model incorporating polyamine binding, H+ binding and surface charge screening.     

Redox Mechanism of S-Nitrosothiol Modulation of Neuronal CaV3.2 T-Type Calcium Channels

T-type calcium channels in the dorsal root ganglia (DRG) have a central function in tuning neuronal excitability and are implicated in sensory processing including pain. Previous studies have implicated redox agents in control of T-channel activity; however, the mechanisms involved are not completely understood. Here, we recorded T-type calcium currents from acutely dissociated DRG neurons from young rats and investigated the mechanisms of Ca_V3.2 T-type channel modulation by S-nitrosothiols (SNOs). We found that extracellular application of S-nitrosoglutathione (GSNO) and S-nitroso-N-acetyl-penicillamine rapidly reduced T-type current amplitudes. GSNO did not affect voltage dependence of steady-state inactivation and macroscopic current kinetics of T-type channels. The effects of GSNO were abolished by pretreatment of the cells with N-ethylmaleimide, an irreversible alkylating agent, but not by pretreatment with 1H-(1,2,4) oxadiazolo (4,3-a) quinoxalin-1-one, a specific soluble guanylyl cyclase inhibitor, suggesting a potential effect of GSNO on putative extracellular thiol residues on T-type channels. Expression of wild-type Ca_V3.2 channels or a quadruple Cys-Ala mutant in human embryonic kidney cells revealed that Cys residues in repeats I and II on the extracellular face of the channel were required for channel inhibition by GSNO. We propose that SNO-related molecules in vivo may lead to alterations of T-type channel-dependent neuronal excitability in sensory neurons and in the central nervous system in both physiological and pathological conditions such as neuronal ischemia/hypoxia.     

Modulation of Calcium-dependent Chloride Secretion by Basolateral SK4-like Channels in a Human Bronchial Cell Line

The human bronchial cell line16HBE14o– was used as a model of airway epithelial cells to study the Ca²⁺-dependent Cl^– secretion and the identity of K_Ca channels involved in the generation of a favorable driving force for Cl^– exit. After ionomycin application, a calcium-activated short-circuit current (I _sc) developed, presenting a transient peak followed by a plateau phase. Both phases were inhibited to different degrees by NFA, glybenclamide and NPPB but DIDS was only effective on the peak phase. ⁸⁶Rb effluxes through both apical and basolateral membranes were stimulated by calcium, blocked by charybdotoxin, clotrimazole and TPA. 1-EBIO, a SK-channel opener, stimulated ⁸⁶Rb effluxes. Block of basolateral K_Ca channels resulted in I _sc inhibition but, while reduced, I _sc was still observed if mucosal Cl^– was lowered. Among SK family members, only SK4 and SK1 mRNAs were detected by RT-PCR. KCNQ1 mRNAs were also identified, but involvement of K_cAMP channels in Cl^– secretion was unlikely, since cAMP application had no effect on ⁸⁶Rb effluxes. Moreover, chromanol 293B or clofilium, specific inhibitors of KCNQ1 channels, had no effect on cAMP-dependent I _sc. In conclusion, two distinct components of Cl^– secretion were identified by a pharmacological approach after a Ca _i ²⁺ rise. K_Ca channels presenting the pharmacology of SK4 channels are present on both apical and basolateral membranes, but it is the basolateral SK4-like channels that play a major role in calcium-dependent chloride secretion in 16HBE14o– cells.     

Multifaceted Modulation of K+ Channels by Protein-tyrosine Phosphatase {epsilon} Tunes Neuronal Excitability

Non-receptor-tyrosine kinases (protein-tyrosine kinases) and non-receptor tyrosine phosphatases (PTPs) have been implicated in the regulation of ion channels, neuronal excitability, and synaptic plasticity. We previously showed that protein-tyrosine kinases such as Src kinase and PTPs such as PTPα and PTPε modulate the activity of delayed-rectifier K(+) channels (I(K)). Here we show cultured cortical neurons from PTPε knock-out (EKO) mice to exhibit increased excitability when compared with wild type (WT) mice, with larger spike discharge frequency, enhanced fast after-hyperpolarization, increased after-depolarization, and reduced spike width. A decrease in I(K) and a rise in large-conductance Ca(2+)-activated K(+) currents (mBK) were observed in EKO cortical neurons compared with WT. Parallel studies in transfected CHO cells indicate that Kv1.1, Kv1.2, Kv7.2/7.3, and mBK are plausible molecular correlates of this multifaceted modulation of K(+) channels by PTPε. In CHO cells, Kv1.1, Kv1.2, and Kv7.2/7.3 K(+) currents were up-regulated by PTPε, whereas mBK channel activity was reduced. The levels of tyrosine phosphorylation of Kv1.1, Kv1.2, Kv7.3, and mBK potassium channels were increased in the brain cortices of neonatal and adult EKO mice compared with WT, suggesting that PTPε in the brain modulates these channel proteins. Our data indicate that in EKO mice, the lack of PTPε-mediated dephosphorylation of Kv1.1, Kv1.2, and Kv7.3 leads to decreased I(K) density and enhanced after-depolarization. In addition, the deficient PTPε-mediated dephosphorylation of mBK channels likely contributes to enhanced mBK and fast after-hyperpolarization, spike shortening, and consequent increase in neuronal excitability observed in cortical neurons from EKO mice.     

Peculiarities of Ion Channels and Modulation of Their Functions in Neurons Belonging to the Nociceptive System

This review deals with the questions related to the composition of ion channels in the membranes of neurons belonging to the nociceptive system; special attention is focused on channels belonging to the TRP family.The factors (in particular, genetically determined) influencing the activity of these channels are discussed. The roles of certain enzymes (protein kinases, phospholipases, etc.) in modulation of the functioning of channel structures typical of nociceptive neurons are reviewed. The roles of calcium transmembrane currents and the state of cellular calcium-controlling compartments in transmission of nociceptive signals are also discussed. Special attention is paid to long-lasting modulatory changes in the activity of different ion channels responsible for the development of stable shifts of sensitive abilities of the nociceptive system (hyperalgesia, hypoalgesia, and allodynia) typical of certain neurological disorders.     

Modulation of Phosphorylation of Neuronal Cytoskeletal Proteins by Neuronal Depolarization

1. The neuronal cytoskeletal protein tau and the carboxy tails of cytoskeletal proteins neurofilament-M (NF-M) and neurofilament-H (NF-H) are phosphorylated on serine residues by the cyclin-dependent kinase cdk-5.2. In aggregating neuronal–glial cultures we show that veratridine-mediated cation influx causes dephosphorylation of tau, NF-M and NF-H. Dephosphorylation was blocked specifically by cyclosporine A but not by okadiac acid at concentrations up to 200 nM.3. These results suggest that veratridine-triggered cation influx causes activation of PP-2B (calcineurin) leading to dephosphorylation of these cytoskeletal proteins.     

Neuronal Calcium Sensor-1 Regulation of Calcium Channels,Secretion, and Neuronal Outgrowth

Calcium (Ca²⁺) is an important intracellular messenger underlying cell physiology. Ca²⁺ channels are the main entry route for Ca²⁺ into excitable cells, and regulate processes such as neurotransmitter release and neuronal outgrowth. Neuronal Calcium Sensor-1 (NCS-1) is a member of the Calmodulin superfamily of EF-hand Ca²⁺ sensing proteins residing in the subfamily of NCS proteins. NCS-1 was originally discovered in Drosophila as an overexpression mutant (Frequenin), having an increased frequency of Ca²⁺-evoked neurotransmission. NCS-1 is N-terminally myristoylated, can bind intracellular membranes, and has a Ca²⁺ affinity of 0.3 μM. Over 10 years ago it was discovered that NCS-1 overexpression enhances Ca²⁺-evoked secretion in bovine adrenal chromaffin cells. The mechanism was unclear, but there was no apparent direct effect on the exocytotic machinery. It was revealed, again in chromaffin cells, that NCS-1 regulates voltage-gated Ca²⁺ channels (Cavs) in G-Protein Coupled Receptor (GPCR) signaling pathways. This work in chromaffin cells highlighted NCS-1 as an important modulator of neurotransmission. NCS-1 has since been shown to regulate and/or directly interact with many proteins including Cavs (P/Q, N, and L), TRPC1/5 channels, GPCRs, IP3R, and PI4 kinase type IIIβ. NCS-1 also affects neuronal outgrowth having roles in learning and memory affecting both short- and long-term synaptic plasticity. It is not known if NCS-1 affects neurotransmission and synaptic plasticity via its effect on PIP2 levels, and/or via a direct interaction with Ca²⁺ channels or their signaling complexes. This review gives a historical account of NCS-1 function, examining contributions from chromaffin cells, PC12 cells and other models, to describe how NCS-1’s regulation of Ca²⁺ channels allows it to exert its physiological effects.     

Modulation of Ionotropic Glutamate Receptor Channels

Glutamate is the major excitatory neurotransmitter in the brain. It acts at ligand-gated cationic channels (NMDA, AMPA and kainate receptors) and at G protein-coupled metabotropic glutamate receptors as well. The glutamatergic transmission is suggested to be involved in development, learning and memory. Its dysfunction can be detected in epilepsy, stroke, neurodegenerative disorders and drug abuse. This paper summarizes the present knowledge on the modulation of glutamate-gated ion channels in the central nervous system by phosphorylation. An inhibitory interaction between adenosine A_2A receptors and NMDA receptors in the neostriatum is described as an example, mediated by the phospholipase C/inositol trisphosphate/calmodulin and calmodulin kinase II pathway.     

Opioid Receptor Regulation of Neuronal Voltage-Gated Calcium Channels

Neuronal voltage-gated calcium channels play a pivotal role in the conversion of electrical signals into calcium entry into nerve endings that is required for the release of neurotransmitters. They are under the control of a number of cellular signaling pathways that serve to fine tune synaptic activities, including G-protein coupled receptors (GPCRs) and the opioid system. Besides modulating channel activity via activation of second messengers, GPCRs also physically associate with calcium channels to regulate their function and expression at the plasma membrane. In this mini review, we discuss the mechanisms by which calcium channels are regulated by classical opioid and nociceptin receptors. We highlight the importance of this regulation in the control of neuronal functions and their implication in the development of disease conditions. Finally, we present recent literature concerning the use of novel μ-opioid receptor/nociceptin receptor modulators and discuss their use as potential drug candidates for the treatment of pain.

     

锌离子对配体门控型离子通道的调节作用

在中枢神经系统(central nervous system,CNS)中,锌离子对配体门控型离子通道具有重要的调节作用。锌离子随着神经元的活动从突触前膜的囊泡中释放到突触间隙,对突触内受体进行调控。锌离子抑制N-甲基-D-天冬氨酸(N-methyl-D-aspartate,NMDA)型谷氨酸受体的活性,而对非NMDA型谷氨酸受体的调控具有多样性。由γ氨基丁酸(γ-aminobutyric acid,GABA)受体所介导的抑制性突触传递活动也受到锌离子的抑制;而锌离子对glycine受体则呈现出浓度依赖的双向调节效应。病理条件下,锌离子参与了兴奋性细胞毒作用所触发的神经元凋亡过程。本文主要阐述了在CNS中,锌离子对配体门控型离子通道所介导的突触传递活动的调控作用,以及这些调控作用的生理功能和病理意义。     

植物环核苷酸门控离子通道基因的功能及其调控

环核苷酸(cAMP/cGMP)是生命体重要的信号分子,环核苷酸门控离子通道(CNGC)是环核苷酸主要的受体之一,目前已在植物中克隆并鉴定了多个环核苷酸门控离子通道基因,它们参与调控植物的生长、发育以及抗病等反应.这些通道既可通过一价阳离子,也可通过二价阳离子,其活性受Ca2+/Calmodulin调控.本文概括了近年来植物环核苷酸门控离子通道(CNGC)基因的克隆、植物CNGC对离子的选择特性、CNGC的生物学功能与调控等方面的研究进展.     

Physiological and Pathological Functions of Mechanosensitive Ion Channels

Rapid sensation of mechanical stimuli is often mediated by mechanosensitve ion channels. Their opening results from conformational changes induced by mechanical forces. It leads to membrane permeation of selected ions and thereby to electrical signaling. Newly identified mechanosensitive ion channels are emerging at an astonishing rate, including some that are traditionally assigned for completely different functions. In this review, we first provide a brief overview of ion channels that are known to play a role in mechanosensation. Next, we focus on three representative ones, including the transient receptor potential channel V4 (TRPV4), Kv1.1 voltage-gated potassium (Kv) channel, and Piezo channels. Their structures, biophysical properties, expression and targeting patterns, and physiological functions are highlighted. The potential role of their mechanosensation in related diseases is further discussed. In sum, mechanosensation appears to be achieved in a variety of ways by different proteins and plays a fundamental role in the function of various organs under normal and abnormal conditions.     

Cross-Correlation Functions for a Neuronal Model

Cross-correlation functions, R_XY(t,τ), are obtained for a neuron model which is characterized by constant threshold θ, by resetting to resting level after an output, and by membrane potential U(t) which results from linear summation of excitatory postsynaptic potentials h(t). The results show that: (1) Near time lag τ = 0, R_XY(t,τ) = f_U [θ-h(τ), t + τ] {h′(τ) + E_U [u′(t + τ)]} for positive values of this quantity, where f_U(u,t) is the probability density function of U(t) and E_U [u′(t + τ)] is the mean value function of U′(t + τ). (2) Minima may appear in R_XY(t,τ) for a neuron subjected only to excitation. (3) For large τ, R_XY(t,τ) is given approximately by the convolution of the input autocorrelation function with the functional of point (1). (4) R_XY(t,τ) is a biased estimator of the shape of h(t), generally over-estimating both its time to peak and its rise time.     

Modulation of Potassium Channels Inhibits Bunyavirus Infection

Bunyaviruses are considered to be emerging pathogens facilitated by the segmented nature of their genome that allows reassortment between different species to generate novel viruses with altered pathogenicity. Bunyaviruses are transmitted via a diverse range of arthropod vectors, as well as rodents, and have established a global disease range with massive importance in healthcare, animal welfare, and economics. There are no vaccines or anti-viral therapies available to treat human bunyavirus infections and so development of new anti-viral strategies is urgently required. Bunyamwera virus (BUNV; genus Orthobunyavirus) is the model bunyavirus, sharing aspects of its molecular and cellular biology with all Bunyaviridae family members. Here, we show for the first time that BUNV activates and requires cellular potassium (K⁺) channels to infect cells. Time of addition assays using K⁺ channel modulating agents demonstrated that K⁺ channel function is critical to events shortly after virus entry but prior to viral RNA synthesis/replication. A similar K⁺ channel dependence was identified for other bunyaviruses namely Schmallenberg virus (Orthobunyavirus) as well as the more distantly related Hazara virus (Nairovirus). Using a rational pharmacological screening regimen, two-pore domain K⁺ channels (K_2P) were identified as the K⁺ channel family mediating BUNV K⁺ channel dependence. As several K_2P channel modulators are currently in clinical use, our work suggests they may represent a new and safe drug class for the treatment of potentially lethal bunyavirus disease.     

Photochromic Modulation of Cys-loop Ligand-gated Ion Channels

Journal of Evolutionary Biochemistry and Physiology - Advances in molecular and cellular biology, as well as the development of chemical synthesis and modern technologies, enriched the contemporary...     

Acidosis,Acid-Sensing Ion Channels,and Neuronal Cell Death

Acidosis is a common feature of many neuronal diseases and often accompanied with adverse consequences such as pain and neuronal injury. Before the discovery of acid-sensing ion channels (ASICs), protons were usually considered as a modulator of other ion channels, such as voltage-gated calcium channels, N-methyl-d-aspartate, and γ-amino butyric acid(A) receptor channels. Accordingly, the functional effects of acidosis were considered as consequences of modulations of these channels. Since the first cloning of ASICs in 1997, the conventional view on acidosis-mediated pain and cell injury has been dramatically changed. To date, ASICs, which are directly activated by extracellular protons, are shown to mediate most of the acidosis-associated physiological and pathological functions. For example, ASIC1a channels are reported to mediate acidosis-induced ischemic neuronal death. In this article, we will review the possible mechanisms that underlie ASIC1a channel-mediated neuronal death and discuss ASIC1a channel modulators involved in this process.