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Boda D, Valiskó M, Gillespie D. Modeling the Device Behavior of Biological and Synthetic Nanopores with Reduced Models. ENTROPY 2020; 22:e22111259. [PMID: 33287027 PMCID: PMC7711659 DOI: 10.3390/e22111259] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 10/30/2020] [Accepted: 11/02/2020] [Indexed: 01/08/2023]
Abstract
Biological ion channels and synthetic nanopores are responsible for passive transport of ions through a membrane between two compartments. Modeling these ionic currents is especially amenable to reduced models because the device functions of these pores, the relation of input parameters (e.g., applied voltage, bath concentrations) and output parameters (e.g., current, rectification, selectivity), are well defined. Reduced models focus on the physics that produces the device functions (i.e., the physics of how inputs become outputs) rather than the atomic/molecular-scale physics inside the pore. Here, we propose four rules of thumb for constructing good reduced models of ion channels and nanopores. They are about (1) the importance of the axial concentration profiles, (2) the importance of the pore charges, (3) choosing the right explicit degrees of freedom, and (4) creating the proper response functions. We provide examples for how each rule of thumb helps in creating a reduced model of device behavior.
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Affiliation(s)
- Dezső Boda
- Department of Physical Chemistry, University of Pannonia, P.O. Box 158, H-8201 Veszprém, Hungary;
- Correspondence: ; Tel.: +36-88-624-000 (ext. 6041)
| | - Mónika Valiskó
- Department of Physical Chemistry, University of Pannonia, P.O. Box 158, H-8201 Veszprém, Hungary;
| | - Dirk Gillespie
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL 60612, USA;
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2
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Zhang X, Xin P, Yoast RE, Emrich SM, Johnson MT, Pathak T, Benson JC, Azimi I, Gill DL, Monteith GR, Trebak M. Distinct pharmacological profiles of ORAI1, ORAI2, and ORAI3 channels. Cell Calcium 2020; 91:102281. [PMID: 32896813 DOI: 10.1016/j.ceca.2020.102281] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 08/25/2020] [Accepted: 08/25/2020] [Indexed: 12/18/2022]
Abstract
The ubiquitous Ca2+ release-activated Ca2+ (CRAC) channel is crucial to many physiological functions. Both gain and loss of CRAC function is linked to disease. While ORAI1 is a crucial subunit of CRAC channels, recent evidence suggests that ORAI2 and ORAI3 heteromerize with ORAI1 to form native CRAC channels. Furthermore, ORAI2 and ORAI3 can form CRAC channels independently of ORAI1, suggesting diverse native CRAC stoichiometries. Yet, most available CRAC modifiers are presumed to target ORAI1 with little knowledge of their effects on ORAI2/3 or heteromers of ORAIs. Here, we used ORAI1/2/3 triple-null cells to express individual ORAI1, ORAI2, ORAI3 or ORAI1/2/3 concatemers. We reveal that GSK-7975A and BTP2 essentially abrogate ORAI1 and ORAI2 activity while causing only a partial inhibition of ORAI3. Interestingly, Synta66 abrogated ORAI1 channel function, while potentiating ORAI2 with no effect on ORAI3. CRAC channel activities mediated by concatenated ORAI1-1, ORAI1-2 and ORAI1-3 dimers were inhibited by Synta66, while ORAI2-3 dimers were unaffected. The CRAC enhancer IA65 significantly potentiated ORAI1 and ORAI1-1 activity with marginal effects on other ORAIs. Further, we characterized the profiles of individual ORAI isoforms in the presence of Gd3+ (5μM), 2-APB (5 μM and 50 μM), as well as changes in intracellular and extracellular pH. Our data reveal unique pharmacological features of ORAI isoforms expressed in an ORAI-null background and provide new insights into ORAI isoform selectivity of widely used CRAC pharmacological compounds.
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Affiliation(s)
- Xuexin Zhang
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA.
| | - Ping Xin
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Ryan E Yoast
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Scott M Emrich
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Martin T Johnson
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Trayambak Pathak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - J Cory Benson
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Iman Azimi
- School of Pharmacy and Pharmacology, College of Health and Medicine, University of Tasmania, Hobart 7001, Tasmania, Australia
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA
| | - Gregory R Monteith
- School of Pharmacy, The University of Queensland, Brisbane 4072, Queensland, Australia
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA; Penn State Cancer Institute, The Pennsylvania State University College of Medicine, 500 University Dr. Hershey, PA, 17033 USA.
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3
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Sárközi S, Komáromi I, Jóna I, Almássy J. Lanthanides Report Calcium Sensor in the Vestibule of Ryanodine Receptor. Biophys J 2017; 112:2127-2137. [PMID: 28538150 DOI: 10.1016/j.bpj.2017.03.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 03/11/2017] [Accepted: 03/23/2017] [Indexed: 02/07/2023] Open
Abstract
Ca2+ regulates ryanodine receptor's (RyR) activity through an activating and an inhibiting Ca2+-binding site located on the cytoplasmic side of the RyR channel. Their altered sensitivity plays an important role in the pathology of malignant hyperthermia and heart failure. We used lanthanide ions (Ln3+) as probes to investigate the Ca2+ sensors of RyR, because they specifically bind to Ca2+-binding proteins and they are impermeable to the channel. Eu3+'s and Sm3+'s action was tested on single RyR1 channels reconstituted into planar lipid bilayers. When the activating binding site was saturated by 50 μM Ca2+, Ln3+ potently inhibited RyR's open probability (Kd Eu3+ = 167 ± 5 nM and Kd Sm3+ = 63 ± 3 nM), but in nominally 0 [Ca2+], low [Eu3+] activated the channel. These results suggest that Ln3+ acts as an agonist of both Ca2+-binding sites. More importantly, the voltage-dependent characteristics of Ln3+'s action led to the conclusion that the activating Ca2+ binding site is located within the electrical field of the channel (in the vestibule). This idea was tested by applying the pore blocker toxin maurocalcine on the cytoplasmic side of RyR. These experiments showed that RyR lost reactivity to changing cytosolic [Ca2+] from 50 μM to 100 nM when the toxin occupied the vestibule. These results suggest that maurocalcine mechanically prevented Ca2+ from dissociating from its binding site and support our vestibular Ca2+ sensor-model further.
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Affiliation(s)
- Sándor Sárközi
- Department of Physiology, Faculty of Medicine, Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - István Komáromi
- Division of Clinical Laboratory Science, Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - István Jóna
- Department of Physiology, Faculty of Medicine, Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - János Almássy
- Department of Physiology, Faculty of Medicine, Department of Laboratory Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
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Voltage-gated calcium channels: Determinants of channel function and modulation by inorganic cations. Prog Neurobiol 2015; 129:1-36. [PMID: 25817891 DOI: 10.1016/j.pneurobio.2014.12.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 12/15/2014] [Accepted: 12/27/2014] [Indexed: 11/20/2022]
Abstract
Voltage-gated calcium channels (VGCCs) represent a key link between electrical signals and non-electrical processes, such as contraction, secretion and transcription. Evolved to achieve high rates of Ca(2+)-selective flux, they possess an elaborate mechanism for selection of Ca(2+) over foreign ions. It has been convincingly linked to competitive binding in the pore, but the fundamental question of how this is reconcilable with high rates of Ca(2+) transfer remains unanswered. By virtue of their similarity to Ca(2+), polyvalent cations can interfere with the function of VGCCs and have proven instrumental in probing the mechanisms underlying selective permeation. Recent emergence of crystallographic data on a set of Ca(2+)-selective model channels provides a structural framework for permeation in VGCCs, and warrants a reconsideration of their diverse modulation by polyvalent cations, which can be roughly separated into three general mechanisms: (I) long-range interactions with charged regions on the surface, affecting the local potential sensed by the channel or influencing voltage-sensor movement by repulsive forces (electrostatic effects), (II) short-range interactions with sites in the ion-conducting pathway, leading to physical obstruction of the channel (pore block), and in some cases (III) short-range interactions with extracellular binding sites, leading to non-electrostatic modifications of channel gating (allosteric effects). These effects, together with the underlying molecular modifications, provide valuable insights into the function of VGCCs, and have important physiological and pathophysiological implications. Allosteric suppression of some of the pore-forming Cavα1-subunits (Cav2.3, Cav3.2) by Zn(2+) and Cu(2+) may play a major role for the regulation of excitability by endogenous transition metal ions. The fact that these ions can often traverse VGCCs can contribute to the detrimental intracellular accumulation of metal ions following excessive release of endogenous Cu(2+) and Zn(2+) or exposure to non-physiological toxic metal ions.
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Nosal OV, Lyubanova OP, Naidenov VG, Shuba YM. Complex modulation of Ca(v)3.1 T-type calcium channel by nickel. Cell Mol Life Sci 2013; 70:1653-61. [PMID: 23250353 PMCID: PMC11113523 DOI: 10.1007/s00018-012-1225-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2012] [Revised: 11/20/2012] [Accepted: 11/27/2012] [Indexed: 11/24/2022]
Abstract
Nickel is considered to be a selective blocker of low-voltage-activated T-type calcium channel. Recently, the Ni(2+)-binding site with critical histidine-191 (H191) within the extracellular IS3-IS4 domain of the most Ni(2+)-sensitive Cav3.2 T-channel isoform has been identified. All calcium channels are postulated to also have intrapore-binding site limiting maximal current carried by permeating divalent cations (PDC) and determining the blockade by non-permeating ones. However, the contribution of the two sites to the overall Ni(2+) effect and its dependence on PDC remain uncertain. Here we compared Ni(2+) action on the wild-type "Ni(2+)-insensitive" Cav3.1w/t channel and Cav3.1Q172H mutant having glutamine (Q) equivalent to H191 of Cav3.2 replaced by histidine. Each channel was expressed in Xenopus oocytes, and Ni(2+) blockade of Ca(2+), Sr(2+), or Ba(2+) currents was assessed by electrophysiology. Inhibition of Cav3.1w/t by Ni(2+) conformed to two sites binding. Ni(2+) binding with high-affinity site (IC50 = 0.03-3 μM depending on PDC) produced maximal inhibition of 20-30% and was voltage-dependent, consistent with its location within the channel's pore. Most of the inhibition (70-80%) was produced by Ni(2+) binding with low-affinity site (IC50 = 240-700 μM). Q172H-mutation mainly affected low-affinity binding (IC50 = 120-160 μM). The IC50 of Ni(2+) binding with both sites in the Cav3.1w/t and Cav3.1Q172H was differentially modulated by PDC, suggesting a varying degree of competition of Ca(2+), Sr(2+), or Ba(2+) with Ni(2+). We conclude that differential Ni(2+)-sensitivity of T-channel subtypes is determined only by H-containing external binding sites, which, in the absence of Ni(2+), may be occupied by PDC, influencing in turn the channel's permeation.
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Affiliation(s)
- Olena V. Nosal
- International Center of Molecular Physiology of the National Academy of Sciences of Ukraine, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Physiology, Kiev, Ukraine
| | - Olga P. Lyubanova
- International Center of Molecular Physiology of the National Academy of Sciences of Ukraine, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Physiology, Kiev, Ukraine
| | - Valeri G. Naidenov
- Bogomoletz Institute of Physiology of the National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kiev, 01024 Ukraine
| | - Yaroslav M. Shuba
- International Center of Molecular Physiology of the National Academy of Sciences of Ukraine, Kiev, Ukraine
- Bogomoletz Institute of Physiology of the National Academy of Sciences of Ukraine, Bogomoletz Str., 4, Kiev, 01024 Ukraine
- State Key Laboratory of Molecular and Cellular Physiology, Kiev, Ukraine
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Malasics A, Boda D, Valiskó M, Henderson D, Gillespie D. Simulations of calcium channel block by trivalent cations: Gd(3+) competes with permeant ions for the selectivity filter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:2013-21. [PMID: 20696128 DOI: 10.1016/j.bbamem.2010.08.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2009] [Revised: 07/29/2010] [Accepted: 08/02/2010] [Indexed: 10/19/2022]
Abstract
Current through L-type calcium channels (Ca(V)1.2 or dihydropyridine receptor) can be blocked by micromolar concentrations of trivalent cations like the lanthanide gadolinium (Gd(3+)). It has been proposed that trivalent block is due to ions competing for a binding site in both the open and closed configuration, but possibly with different trivalent affinities. Here, we corroborate this general view of trivalent block by computing conductance of a model L-type calcium channel. The model qualitatively reproduces the Gd(3+) concentration dependence and the effect that substantially more Gd(3+) is required to produce similar block in the presence of Sr(2+) (compared to Ba(2+)) and even more in the presence of Ca(2+). Trivalent block is explained in this model by cations binding in the selectivity filter with the charge/space competition mechanism. This is the same mechanism that in the model channel governs other selectivity properties. Specifically, selectivity is determined by the combination of ions that most effectively screen the negative glutamates of the protein while finding space in the midst of the closely packed carboxylate groups of the glutamate residues.
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Affiliation(s)
- Attila Malasics
- Department of Physical Chemistry, University of Pannonia, Veszprém, Hungary
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7
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Tadross MR, Ben Johny M, Yue DT. Molecular endpoints of Ca2+/calmodulin- and voltage-dependent inactivation of Ca(v)1.3 channels. ACTA ACUST UNITED AC 2010; 135:197-215. [PMID: 20142517 PMCID: PMC2828906 DOI: 10.1085/jgp.200910308] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Ca2+/calmodulin- and voltage-dependent inactivation (CDI and VDI) comprise vital prototypes of Ca2+ channel modulation, rich with biological consequences. Although the events initiating CDI and VDI are known, their downstream mechanisms have eluded consensus. Competing proposals include hinged-lid occlusion of channels, selectivity filter collapse, and allosteric inhibition of the activation gate. Here, novel theory predicts that perturbations of channel activation should alter inactivation in distinctive ways, depending on which hypothesis holds true. Thus, we systematically mutate the activation gate, formed by all S6 segments within CaV1.3. These channels feature robust baseline CDI, and the resulting mutant library exhibits significant diversity of activation, CDI, and VDI. For CDI, a clear and previously unreported pattern emerges: activation-enhancing mutations proportionately weaken inactivation. This outcome substantiates an allosteric CDI mechanism. For VDI, the data implicate a “hinged lid–shield” mechanism, similar to a hinged-lid process, with a previously unrecognized feature. Namely, we detect a “shield” in CaV1.3 channels that is specialized to repel lid closure. These findings reveal long-sought downstream mechanisms of inactivation and may furnish a framework for the understanding of Ca2+ channelopathies involving S6 mutations.
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Affiliation(s)
- Michael R Tadross
- Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Abstract
CRAC channels generate Ca(2+) signals critical for the activation of immune cells and exhibit an intriguing pore profile distinguished by extremely high Ca(2+) selectivity, low Cs(+) permeability, and small unitary conductance. To identify the ion conduction pathway and gain insight into the structural bases of these permeation characteristics, we introduced cysteine residues in the CRAC channel pore subunit, Orai1, and probed their accessibility to various thiol-reactive reagents. Our results indicate that the architecture of the ion conduction pathway is characterized by a flexible outer vestibule formed by the TM1-TM2 loop, which leads to a narrow pore flanked by residues of a helical TM1 segment. Residues in TM3, and specifically, E190, a residue considered important for ion selectivity, are not close to the pore. Moreover, the outer vestibule does not significantly contribute to ion selectivity, implying that Ca(2+) selectivity is conferred mainly by E106. The ion conduction pathway is sufficiently narrow along much of its length to permit stable coordination of Cd(2+) by several TM1 residues, which likely explains the slow flux of ions within the restrained geometry of the pore. These results provide a structural framework to understand the unique permeation properties of CRAC channels.
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Srikanth S, Jung HJ, Ribalet B, Gwack Y. The intracellular loop of Orai1 plays a central role in fast inactivation of Ca2+ release-activated Ca2+ channels. J Biol Chem 2009; 285:5066-75. [PMID: 20007711 DOI: 10.1074/jbc.m109.072736] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Store-operated Ca(2+) entry (SOCE) due to activation of Ca(2+) release-activated Ca(2+) (CRAC) channels leads to sustained elevation of cytoplasmic Ca(2+) and activation of lymphocytes. CRAC channels consisting of four pore-forming Orai1 subunits are activated by STIM1, an endoplasmic reticulum Ca(2+) sensor that senses intracellular store depletion and migrates to plasma membrane proximal regions to mediate SOCE. One of the fundamental properties of CRAC channels is their Ca(2+)-dependent fast inactivation. To identify the domains of Orai1 involved in fast inactivation, we have mutated residues in the Orai1 intracellular loop linking transmembrane segment II to III. Mutation of four residues, V(151)SNV(154), at the center of the loop (MutA) abrogated fast inactivation, leading to increased SOCE as well as higher CRAC currents. Point mutation analysis identified five key amino acids, N(153)VHNL(157), that increased SOCE in Orai1 null murine embryonic fibroblasts. Expression or direct application of a peptide comprising the entire intracellular loop or the sequence N(153)VHNL(157) blocked CRAC currents from both wild type (WT) and MutA Orai1. A peptide incorporating the MutA mutations had no blocking effect. Concatenated Orai1 constructs with four MutA monomers exhibited high CRAC currents lacking fast inactivation. Reintroduction of a single WT monomer (MutA-MutA-MutA-WT) was sufficient to fully restore fast inactivation, suggesting that only a single intracellular loop can block the channel. These data suggest that the intracellular loop of Orai1 acts as an inactivation particle, which is stabilized in the ion permeation pathway by the N(153)VHNL(157) residues. These results along with recent reports support a model in which the N terminus and the selectivity filter of Orai1 as well as STIM1 act in concert to regulate the movement of the intracellular loop and evoke fast inactivation.
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Affiliation(s)
- Sonal Srikanth
- Department of Physiology, UCLA, Los Angeles, California 90095, USA
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Obejero-Paz CA, Gray IP, Jones SW. Ni2+ block of CaV3.1 (alpha1G) T-type calcium channels. ACTA ACUST UNITED AC 2008; 132:239-50. [PMID: 18663132 PMCID: PMC2483332 DOI: 10.1085/jgp.200809988] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ni2+ inhibits current through calcium channels, in part by blocking the pore, but Ni2+ may also allosterically affect channel activity via sites outside the permeation pathway. As a test for pore blockade, we examined whether the effect of Ni2+ on CaV3.1 is affected by permeant ions. We find two components to block by Ni2+, a rapid block with little voltage dependence, and a slow block most visible as accelerated tail currents. Rapid block is weaker for outward vs. inward currents (apparent Kd = 3 vs. 1 mM Ni2+, with 2 mM Ca2+ or Ba2+) and is reduced at high permeant ion concentration (110 vs. 2 mM Ca2+ or Ba2+). Slow block depends both on the concentration and on the identity of the permeant ion (Ca2+ vs. Ba2+ vs. Na+). Slow block is 2–3× faster in Ba2+ than in Ca2+ (2 or 110 mM), and is ∼10× faster with 2 vs. 110 mM Ca2+ or Ba2+. Slow block is orders of magnitude slower than the diffusion limit, except in the nominal absence of divalent cations (∼3 μM Ca2+). We conclude that both fast and slow block of CaV3.1 by Ni2+ are most consistent with occlusion of the pore. The exit rate of Ni2+ for slow block is reduced at high Ni2+ concentrations, suggesting that the site responsible for fast block can “lock in” slow block by Ni2+, at a site located deeper within the pore. In contrast to the complex pore block observed for CaV3.1, inhibition of CaV3.2 by Ni2+ was essentially independent of voltage, and was similar in 2 mM Ca2+ vs. Ba2+, consistent with inhibition by a different mechanism, at a site outside the pore.
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Affiliation(s)
- Carlos A Obejero-Paz
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
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Abstract
A hallmark of the GABA projection neurons of the substantia nigra pars reticulata (SNr), a key basal ganglia output nucleus, is its depolarized membrane potential and rapid spontaneous spikes that encode the basal ganglia output. Parkinsonian movement disorders are often associated with abnormalities in SNr GABA neuron firing intensity and/or pattern. A fundamental question remains regarding the molecular identity of the ion channels that drive these neurons to a depolarized membrane potential. We show here that SNr GABA projection neurons selectively express type 3 canonical transient receptor potential (TRPC3) channels. These channels are tonically active and mediate an inward, Na+-dependent current, leading to a substantial depolarization in these neurons. Inhibition of TRPC3 channels induces hyperpolarization, decreases firing frequency, and increases firing irregularity. These data demonstrate that TRPC3 channels play important roles in ensuring the appropriate firing intensity and pattern in SNr GABA projection neurons that are crucial to movement control.
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Affiliation(s)
- Riccardo Olcese
- Division of Molecular Medicine, Department of Anesthesiology, Brain Research Institute and Cardiovascular Research Laboratories, D. Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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Babich O, Matveev V, Harris AL, Shirokov R. Ca2+-dependent inactivation of CaV1.2 channels prevents Gd3+ block: does Ca2+ block the pore of inactivated channels? ACTA ACUST UNITED AC 2007; 129:477-83. [PMID: 17535960 PMCID: PMC2151623 DOI: 10.1085/jgp.200709734] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Lanthanide gadolinium (Gd(3+)) blocks Ca(V)1.2 channels at the selectivity filter. Here we investigated whether Gd(3+) block interferes with Ca(2+)-dependent inactivation, which requires Ca(2+) entry through the same site. Using brief pulses to 200 mV that relieve Gd(3+) block but not inactivation, we monitored how the proportions of open and open-blocked channels change during inactivation. We found that blocked channels inactivate much less. This is expected for Gd(3+) block of the Ca(2+) influx that enhances inactivation. However, we also found that the extent of Gd(3+) block did not change when inactivation was reduced by abolition of Ca(2+)/calmodulin interaction, showing that Gd(3+) does not block the inactivated channel. Thus, Gd(3+) block and inactivation are mutually exclusive, suggesting action at a common site. These observations suggest that inactivation causes a change at the selectivity filter that either hides the Gd(3+) site or reduces its affinity, or that Ca(2+) occupies the binding site at the selectivity filter in inactivated channels. The latter possibility is supported by previous findings that the EEQE mutation of the selectivity EEEE locus is void of Ca(2+)-dependent inactivation (Zong Z.Q., J.Y. Zhou, and T. Tanabe. 1994. Biochem. Biophys. Res. Commun. 201:1117-11123), and that Ca(2+)-inactivated channels conduct Na(+) when Ca(2+) is removed from the extracellular medium (Babich O., D. Isaev, and R. Shirokov. 2005. J. Physiol. 565:709-717). Based on these results, we propose that inactivation increases affinity of the selectivity filter for Ca(2+) so that Ca(2+) ion blocks the pore. A minimal model, in which the inactivation "gate" is an increase in affinity of the selectivity filter for permeating ions, successfully simulates the characteristic U-shaped voltage dependence of inactivation in Ca(2+).
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Affiliation(s)
- Olga Babich
- Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, NJ 07103, USA
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