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Mironov SL. Bound Ca 2+ moves faster and farther from single open channels than free Ca 2. Front Physiol 2023; 14:1266120. [PMID: 38173931 PMCID: PMC10761531 DOI: 10.3389/fphys.2023.1266120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Accepted: 11/30/2023] [Indexed: 01/05/2024] Open
Abstract
A concept of Ca2+ nanodomains established in the cytoplasm after opening single-calcium channels helps mechanistically understand the physiological mechanisms of Ca2+ signaling. It predicts standing gradients of cytoplasmic free Ca2+ around single channels in the plasma membrane. The fate of bound Ca2+ attracted much less attention. This study aimed to examine the profiles of Ca2+ bound to low-mobility buffers such as bulky Ca2+-binding proteins. The solution of non-linear PDEs for an immobile buffer predicts fast decay of free [Ca2+] from the channel lumen and the traveling wave for bound Ca2+. For low-mobility buffers like calmodulin, the calculated profiles of free and bound Ca2+ are similar. Theoretical predictions are tested by imaging 1D profiles of Ca2+ bound to low-mobility fluo-4-dextran. The traveling waves of bound Ca2+ are observed that develop during the opening of single channels. The findings tempt to propose that Ca2+ signaling may not be solely related by the absolute free [Ca2+] at the sensor location, which is extremely localized, but determined by the time when a wave of bound Ca2+ reaches a threshold needed for sensor activation.
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Affiliation(s)
- S. L. Mironov
- Institute of Neuro- and Sensory Physiology, Georg-August-University, Göttingen, Germany
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2
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Velázquez IF, Cantiello HF, Cantero MDR. High calcium transport by Polycystin-2 (TRPP2) induces channel clustering and oscillatory currents. Biochem Biophys Res Commun 2023; 660:50-57. [PMID: 37062241 DOI: 10.1016/j.bbrc.2023.03.067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 03/02/2023] [Accepted: 03/28/2023] [Indexed: 04/05/2023]
Abstract
The regulation by Ca2+ of Ca2+-permeable ion channels represents an important mechanism in the control of cell function. Polycystin-2 (PC2, TRPP2), a member of the TRP channel family (Transient Potential Receptor), is a Ca2+ permeable non-selective cation channel. Previous studies from our laboratory demonstrated that physiological concentrations of Ca2+ do not regulate in vitro translated PC2 (PC2iv) channel activity. However, the issue as to PC2's Ca2+ permeability and regulation remain ill-defined, in particular because Ca2+ transport is usually observed in the presence of other ionic gradients. In this study, we assessed Ca2+ transport by PC2iv in a lipid bilayer reconstitution system in a high Ca2+ gradient (CaCl2 100 mM cis, CaCl2 10 mM trans) in the presence of either 3:7 or 7:3 1-palmitoyl-2-oleoyl-choline and ethanolamine lipid mixtures. Reconstituted PC2iv showed spontaneous Ca2+ currents in both lipid mixtures, with a maximum conductance of 63 ± 13 pS (n = 19) and 105 pS ± 9.8 (n = 9), respectively. In both cases, we best fitted the experimental data with the Goldman-Hodgkin-Katz equation, observing a reversal potential (Vrev ∼ -27 mV) consistent with strict Ca2+ selectivity. The R742X mutated PC2 (PC2R742X), lacking the carboxy terminal domain of the channel showed no differences with wild type PC2. Interestingly, we also observed the onset of spontaneous Ca2+ current oscillations whenever PC2-containing samples were reconstituted in the 3:7, but not 7:3 POPC:POPE lipid mixture. The amplitude and frequency of the ionic oscillations were highly dependent on the applied voltage, the imposed Ca2+ gradient, and the presence of high Ca2+, which induced PC2 channel clustering as observed by atomic force microscopy (AFM). We also used the QuB suite to kinetically model the PC2 channel Ca2+ oscillations based on the presence of subconductance states in the channel. The encompassed evidence supports a high Ca2+ permeability by PC2, and a novel oscillatory mechanism dependent on the presence of Ca2+ and phospholipids that provides the first evidence for the relation between stochasticity and deterministic processes mediated by ion channels.
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Affiliation(s)
- Irina F Velázquez
- Laboratorio de Canales Iónicos, Instituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, CONICET-UNSE), Santiago del Estero, Argentina
| | - Horacio F Cantiello
- Laboratorio de Canales Iónicos, Instituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, CONICET-UNSE), Santiago del Estero, Argentina
| | - María Del Rocío Cantero
- Laboratorio de Canales Iónicos, Instituto Multidisciplinario de Salud, Tecnología y Desarrollo (IMSaTeD, CONICET-UNSE), Santiago del Estero, Argentina.
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Wang ZW, Riaz S, Niu L. Roles and Sources of Calcium in Synaptic Exocytosis. ADVANCES IN NEUROBIOLOGY 2023; 33:139-170. [PMID: 37615866 DOI: 10.1007/978-3-031-34229-5_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Calcium ions (Ca2+) play a critical role in triggering neurotransmitter release. The rate of release is directly related to the concentration of Ca2+ at the presynaptic site, with a supralinear relationship. There are two main sources of Ca2+ that trigger synaptic vesicle fusion: influx through voltage-gated Ca2+ channels in the plasma membrane and release from the endoplasmic reticulum via ryanodine receptors. This chapter will cover the sources of Ca2+ at the presynaptic nerve terminal, the relationship between neurotransmitter release rate and Ca2+ concentration, and the mechanisms that achieve the necessary Ca2+ concentrations for triggering synaptic exocytosis at the presynaptic site.
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Affiliation(s)
- Zhao-Wen Wang
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT, USA.
| | - Sadaf Riaz
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT, USA
| | - Longgang Niu
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT, USA
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Maier M, Olthoff S, Hill K, Zosel C, Magauer T, Wein LA, Schaefer M. KS0365, a novel activator of the transient receptor potential vanilloid 3 (TRPV3) channel, accelerates keratinocyte migration. Br J Pharmacol 2022; 179:5290-5304. [PMID: 35916168 DOI: 10.1111/bph.15937] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 06/09/2022] [Accepted: 07/06/2022] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Ca2+ signalling mediated by the thermosensitive, non-selective, Ca2+ -permeable transient receptor potential channel TRPV3 is assumed to play a critical role in regulating several aspects of skin functions, such as keratinocyte proliferation, differentiation, skin barrier formation and wound healing. Studying the function of TRPV3 in skin homeostasis, however, is still constrained by a lack of potent and selective pharmacological modulators of TRPV3. EXPERIMENTAL APPROACH By screening an in-house compound library using fluorometric intracellular Ca2+ assays, we identified two chemically related hits. The more potent and efficient TRPV3 activator KS0365 was further evaluated in fluo-4-assisted Ca2+ assays, different Ca2+ imaging approaches, electrophysiological studies, cytotoxicity and migration assays. KEY RESULTS KS0365 activated recombinant and native mouse TRPV3 more potently and with a higher efficacy compared to 2-APB and did not activate TRPV1, TRPV2 or TRPV4 channels. The activation of TRPV3 by KS0365 super-additively accelerated the EGF-induced keratinocyte migration, which was inhibited by the TRP channel blocker ruthenium red or by siRNA-mediated TRPV3 knockdown. Moreover, KS0365 induced strong Ca2+ responses in migrating front cells and in leading edges of keratinocytes. CONCLUSIONS AND IMPLICATIONS The selective TRPV3 activator KS0365 triggers increases in [Ca2+ ]i with most prominent signals in the leading edge, and accelerates migration of keratinocytes. TRPV3 activators may promote reepithelialization upon skin wounding.
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Affiliation(s)
- Marion Maier
- Leipzig University, Medical Faculty, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Leipzig, Germany
| | - Stefan Olthoff
- Leipzig University, Medical Faculty, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Leipzig, Germany
| | - Kerstin Hill
- Leipzig University, Medical Faculty, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Leipzig, Germany
| | - Carolin Zosel
- Leipzig University, Medical Faculty, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Leipzig, Germany
| | - Thomas Magauer
- Leopold-Franzens-University Innsbruck, Institute of Organic Chemistry and Center for Molecular Biosciences, Innsbruck, Austria
| | - Lukas Anton Wein
- Leopold-Franzens-University Innsbruck, Institute of Organic Chemistry and Center for Molecular Biosciences, Innsbruck, Austria
| | - Michael Schaefer
- Leipzig University, Medical Faculty, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Leipzig, Germany
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Dixon RE, Navedo MF, Binder MD, Santana LF. Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters. Physiol Rev 2021; 102:1159-1210. [PMID: 34927454 DOI: 10.1152/physrev.00022.2021] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Cav1.2 and Cav1.3 channels to obligatory dimeric assembly and gating of voltage-gated Nav1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP3Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.
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Affiliation(s)
- Rose Ellen Dixon
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
| | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, CA, United States
| | - Marc D Binder
- Department of Physiology and Biophysics, University of Washington, Seattle, WA, United States
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, CA, United States
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Langlhofer G, Kogel A, Schaefer M. Glucose-induced [Ca2+]i oscillations in β cells are composed of trains of spikes within a subplasmalemmal microdomain. Cell Calcium 2021; 99:102469. [PMID: 34509871 DOI: 10.1016/j.ceca.2021.102469] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 08/31/2021] [Accepted: 09/01/2021] [Indexed: 10/20/2022]
Abstract
Electrical activity and oscillations of cytosolic Ca2+ concentrations ([Ca2+]i) that trigger insulin release in response to glucose are key functions of pancreatic β cells. Although oscillatory Ca2+ signals have been intensively studied in β cells, their lower frequency did not match that of electrical activity. In addition, the measured peak [Ca2+]i did not reach levels that are typically required by synaptotagmins to elicit the release of insulin-containing vesicles in live-cell experiments. We therefore sought to resolve the Ca2+ dynamics in the subplasmalemmal microdomain that is critical for triggering fast exocytosis. Applying total internal reflection fluorescence (TIRF) microscopy in insulin-producing INS-1E and primary mouse β cells, we resolved extraordinary fast trains of Ca2+ spiking (frequency > 3 s-1) in response to glucose exposure. Using a low-affinity [Ca2+]i indicator dye, we provide experimental evidence that Ca2+ spikes reach low micromolar apparent concentrations in the vicinity of the plasma membrane. Analysis of Ca2+ spikes evoked by repeated depolarization for 10 ms closely matched the Ca2+ dynamics observed upon glucose application. To our knowledge, this is the first study that experimentally demonstrates Ca2+ spikes in β cells with velocities that resemble those of bursting or continuously appearing trains of action potentials (APs) in non-patched cells.
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Affiliation(s)
- Georg Langlhofer
- Rudolf-Boehm-Institute for Pharmacology and Toxicology, University of Leipzig, Leipzig, Germany
| | - Alexander Kogel
- Rudolf-Boehm-Institute for Pharmacology and Toxicology, University of Leipzig, Leipzig, Germany
| | - Michael Schaefer
- Rudolf-Boehm-Institute for Pharmacology and Toxicology, University of Leipzig, Leipzig, Germany.
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Guse AH, Gil Montoya DC, Diercks BP. Mechanisms and functions of calcium microdomains produced by ORAI channels, d-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors. Pharmacol Ther 2021; 223:107804. [PMID: 33465399 DOI: 10.1016/j.pharmthera.2021.107804] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 01/04/2021] [Indexed: 12/24/2022]
Abstract
With the discovery of local Ca2+ signals in the 1990s the concept of 'elementary Ca2+ signals' and 'fundamental Ca2+ signals' was developed. While 'elementary Ca2+signals' relate to optical signals gained by activity of small clusters of Ca2+channels, 'fundamental signals' describe such optical signals that arise from opening of single Ca2+channels. In this review, we discuss (i) concepts of local Ca2+ signals and Ca2+ microdomains, (ii) molecular mechanisms underlying Ca2+ microdomains, (iii) functions of Ca2+ microdomains, and (iv) mathematical modelling of Ca2+ microdomains. We focus on Ca2+ microdomains produced by ORAI channels, D-myo-inositol 1,4,5-trisphosphate receptors, or ryanodine receptors. In summary, research on local Ca2+ signals in different cell models aims to better understand how cells use the Ca2+ toolkit to produce Ca2+ microdomains as relevant signals for specific cellular responses, but also how local Ca2+ signals as building blocks merge into global Ca2+ signaling.
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Affiliation(s)
- Andreas H Guse
- The Calcium Signalling Group, Dept of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
| | - Diana C Gil Montoya
- The Calcium Signalling Group, Dept of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany
| | - Björn-Philipp Diercks
- The Calcium Signalling Group, Dept of Biochemistry and Molecular Cell Biology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany
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9
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Catacuzzeno L, Sforna L, Esposito V, Limatola C, Franciolini F. Ion Channels in Glioma Malignancy. Rev Physiol Biochem Pharmacol 2020; 181:223-267. [DOI: 10.1007/112_2020_44] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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10
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Abstract
Ionized calcium (Ca2+) is the most versatile cellular messenger. All cells use Ca2+ signals to regulate their activities in response to extrinsic and intrinsic stimuli. Alterations in cellular Ca2+ signaling and/or Ca2+ homeostasis can subvert physiological processes into driving pathological outcomes. Imaging of living cells over the past decades has demonstrated that Ca2+ signals encode information in their frequency, kinetics, amplitude, and spatial extent. These parameters alter depending on the type and intensity of stimulation, and cellular context. Moreover, it is evident that different cell types produce widely varying Ca2+ signals, with properties that suit their physiological functions. This primer discusses basic principles and mechanisms underlying cellular Ca2+ signaling and Ca2+ homeostasis. Consequently, we have cited some historical articles in addition to more recent findings. A brief summary of the core features of cellular Ca2+ signaling is provided, with particular focus on Ca2+ stores and Ca2+ transport across cellular membranes, as well as mechanisms by which Ca2+ signals activate downstream effector systems.
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Gilabert JA. Cytoplasmic Calcium Buffering: An Integrative Crosstalk. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:163-182. [PMID: 31646510 DOI: 10.1007/978-3-030-12457-1_7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Calcium (Ca2+) buffering is part of an integrative crosstalk between different mechanisms and elements involved in the control of free Ca2+ ions persistence in the cytoplasm and hence, in the Ca2+-dependence of many intracellular processes. Alterations of Ca2+ homeostasis and signaling from systemic to subcellular levels also play a pivotal role in the pathogenesis of many diseases.Compared with Ca2+ sequestration towards intracellular Ca2+ stores, Ca2+ buffering is a rapid process occurring in a subsecond scale. Any molecule (or binding site) with the ability to bind Ca2+ ions could be considered, at least in principle, as a buffer. However, the term Ca2+ buffer is applied only to a small subset of Ca2+ binding proteins containing acidic side-chain residues.Ca2+ buffering in the cytoplasm mainly relies on mobile and immobile or fixed buffers controlling the diffusion of free Ca2+ ions inside the cytosol both temporally and spatially. Mobility of buffers depends on their molecular weight, but other parameters as their concentration, affinity for Ca2+ or Ca2+ binding and dissociation kinetics next to their diffusional mobility also contribute to make Ca2+ signaling one of the most complex signaling activities of the cell.The crosstalk between all the elements involved in the intracellular Ca2+ dynamics is a process of extreme complexity due to the diversity of structural and molecular elements involved but permit a highly regulated spatiotemporal control of the signal mediated by Ca2+ ions. The basis of modeling tools to study Ca2+ dynamics are also presented.
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Affiliation(s)
- Juan A Gilabert
- Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Complutense University of Madrid, Madrid, Spain.
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12
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Rethinking calcium profiles around single channels: the exponential and periodic calcium nanodomains. Sci Rep 2019; 9:17196. [PMID: 31748584 PMCID: PMC6868209 DOI: 10.1038/s41598-019-53095-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 10/24/2019] [Indexed: 11/25/2022] Open
Abstract
Many fundamental calcium-dependent physiological processes are triggered by high local calcium levels that are established around the sites of calcium entry into the cell (channels). They are dubbed as calcium nanodomains but their exact profiles are still elusive. The concept of calcium nanodomains stems from a linear model of calcium diffusion and is only valid when calcium increases are smaller than the concentration of cytoplasmic buffers. Recent data indicates that much higher calcium levels cause buffer saturation. Therefore, I sought explicit solutions of a nonlinear reaction-diffusion model and found a dichotomous solution. For small fluxes, the steady state calcium profile is quasi-exponential, and when calcium exceeds buffer concentration a spatial periodicity appears. Analytical results are supported by Monte-Carlo simulations. I also imaged 1D- and radial calcium distributions around single α-synuclein channels in cell-free conditions. Measured Ca profiles are consistent with theoretical predictions. I propose that the periodic calcium patterns may well arise under certain conditions and their specific functional role has to be established.
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Shah SI, Demuro A, Mak DOD, Parker I, Pearson JE, Ullah G. TraceSpecks: A Software for Automated Idealization of Noisy Patch-Clamp and Imaging Data. Biophys J 2019; 115:9-21. [PMID: 29972815 DOI: 10.1016/j.bpj.2018.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 05/15/2018] [Accepted: 06/04/2018] [Indexed: 10/28/2022] Open
Abstract
Experimental records of single molecules or ion channels from fluorescence microscopy and patch-clamp electrophysiology often include high-frequency noise and baseline fluctuations that are not generated by the system under investigation and have to be removed. Moreover, multiple channels or conductance levels can be present at a time in the data that need to be quantified to accurately understand the behavior of the system. Manual procedures for removing these fluctuations and extracting conducting states or multiple channels are laborious, prone to subjective bias, and likely to hinder the processing of often very large data sets. We introduce a maximal likelihood formalism for separating signal from a noisy and drifting background such as fluorescence traces from imaging of elementary Ca2+ release events called puffs arising from clusters of channels, and patch-clamp recordings of ion channels. Parameters such as the number of open channels or conducting states, noise level, and background signal can all be optimized using the expectation-maximization algorithm. We implement our algorithm following the Baum-Welch approach to expectation-maximization in the portable Java language with a user-friendly graphical interface and test the algorithm on both synthetic and experimental data from the patch-clamp electrophysiology of Ca2+ channels and fluorescence microscopy of a cluster of Ca2+ channels and Ca2+ channels with multiple conductance levels. The resulting software is accurate, fast, and provides detailed information usually not available through manual analysis. Options for visual inspection of the raw and processed data with key parameters are provided, in addition to a range of statistics such as the mean open probabilities, mean open times, mean close times, dwell-time distributions for different number of channels open or conductance levels, amplitude distribution of all opening events, and number of transitions between different number of open channels or conducting levels in asci format with a single click.
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Affiliation(s)
| | - Angelo Demuro
- Department of Neurobiology and Behavior, University of California, Irvine, Irvine, California
| | - Don-On Daniel Mak
- Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Ian Parker
- Department of Neurobiology and Behavior, University of California, Irvine, Irvine, California; Department of Physiology and Biophysics, University of California, Irvine, Irvine, California
| | - John E Pearson
- Theoretical Biology and Biophysics, Los Alamos National Laboratory, Los Alamos, New Mexico
| | - Ghanim Ullah
- Department of Physics, University of South Florida, Tampa, Florida.
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Nicotine Acts on Cholinergic Signaling Mechanisms to Directly Modulate Choroid Plexus Function. eNeuro 2019; 6:eN-NWR-0051-19. [PMID: 31119189 PMCID: PMC6529591 DOI: 10.1523/eneuro.0051-19.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 03/26/2019] [Accepted: 03/27/2019] [Indexed: 12/23/2022] Open
Abstract
Neuronal cholinergic circuits have been implicated in cognitive function and neurological disease, but the role of cholinergic signaling in other cellular populations within the brain has not been as fully defined. Here, we show that cholinergic signaling mechanisms are involved in mediating the function of the choroid plexus, the brain structure responsible for generating CSF and releasing various factors into the brain. The choroid plexus was found to express markers of endogenous cholinergic signaling, including multiple nicotinic acetylcholine receptor (nAChR) subtypes in a region-specific manner, and application of nicotine was found to induce cellular activation, as evidenced by calcium influx in primary tissue. During intravenous nicotine self-administration in male rats, nicotine increased expression of transthyretin, a protein selectively produced and released by the choroid plexus, and microRNA-204 (mir-204), a transcript found in high levels in the choroid plexus and CSF. Finally, human choroid plexus tissue from both sexes was found to exhibit similar nAChR, transthyretin and mir-204 expression profiles, supporting the translational relevance of the findings. Together, these studies demonstrate functionally active cholinergic signaling mechanisms in the choroid plexus, the resulting effects on transthyretin and mir-204 expression, and reveal the direct mechanism by which nicotine modulates function of this tissue.
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15
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Lock JT, Smith IF, Parker I. Spatial-temporal patterning of Ca 2+ signals by the subcellular distribution of IP 3 and IP 3 receptors. Semin Cell Dev Biol 2019; 94:3-10. [PMID: 30703557 DOI: 10.1016/j.semcdb.2019.01.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 01/17/2019] [Accepted: 01/22/2019] [Indexed: 12/25/2022]
Abstract
The patterning of cytosolic Ca2+ signals in space and time underlies their ubiquitous ability to specifically regulate numerous cellular processes. Signals mediated by liberation of Ca2+ sequestered in the endoplasmic reticulum (ER) through inositol trisphosphate receptor (IP3R) channels constitute a hierarchy of events; ranging from openings of individual IP3 channels, through the concerted openings of several clustered IP3Rs to generate local Ca2+ puffs, to global Ca2+ waves and oscillations that engulf the entire cell. Here, we review recent progress in elucidating how this hierarchy is shaped by an interplay between the functional gating properties of IP3Rs and their spatial distribution within the cell. We focus in particular on the subset of IP3Rs that are organized in stationary clusters and are endowed with the ability to preferentially liberate Ca2+.
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Affiliation(s)
- Jeffrey T Lock
- Department of Neurobiology & Behavior, UC Irvine, Irvine, CA, USA.
| | - Ian F Smith
- Department of Neurobiology & Behavior, UC Irvine, Irvine, CA, USA
| | - Ian Parker
- Department of Neurobiology & Behavior, UC Irvine, Irvine, CA, USA; Department of Physiology & Biophysics, UC Irvine, Irvine, CA, USA
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16
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Shah SI, Smith M, Swaminathan D, Parker I, Ullah G, Demuro A. CellSpecks: A Software for Automated Detection and Analysis of Calcium Channels in Live Cells. Biophys J 2018; 115:2141-2151. [PMID: 30447989 DOI: 10.1016/j.bpj.2018.10.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 09/27/2018] [Accepted: 10/22/2018] [Indexed: 02/01/2023] Open
Abstract
To couple the fidelity of patch-clamp recording with a more high-throughput screening capability, we pioneered a, to our knowledge, novel approach to single-channel recording that we named "optical patch clamp." By using highly sensitive fluorescent Ca2+ indicator dyes in conjunction with total internal fluorescence microscopy techniques, we monitor Ca2+ flux through individual Ca2+-permeable channels. This approach provides information about channel gating analogous to patch-clamp recording at a time resolution of ∼2 ms with the additional advantage of being massively parallel, providing simultaneous and independent recording from thousands of channels in the native environment. However, manual analysis of the data generated by this technique presents severe challenges because a video recording can include many thousands of frames. To overcome this bottleneck, we developed an image processing and analysis framework called CellSpecks capable of detecting and fully analyzing the kinetics of ion channels within a video sequence. By using randomly generated synthetic data, we tested the ability of CellSpecks to rapidly and efficiently detect and analyze the activity of thousands of ion channels, including openings for a few milliseconds. Here, we report the use of CellSpecks for the analysis of experimental data acquired by imaging muscle nicotinic acetylcholine receptors and the Alzheimer's disease-associated amyloid β pores with multiconductance levels in the plasma membrane of Xenopus laevis oocytes. We show that CellSpecks can accurately and efficiently generate location maps and create raw and processed fluorescence time traces; histograms of mean open times, mean close times, open probabilities, durations, and maximal amplitudes; and a "channel chip" showing the activity of all channels as a function of time. Although we specifically illustrate the application of CellSpecks for analyzing data from Ca2+ channels, it can be easily customized to analyze other spatially and temporally localized signals.
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Affiliation(s)
| | | | - Divya Swaminathan
- Department of Neurobiology and Behavior,University of California Irvine, Irvine, California
| | - Ian Parker
- Department of Neurobiology and Behavior,University of California Irvine, Irvine, California; Department of Physiology and Biophysics, University of California Irvine, Irvine, California
| | - Ghanim Ullah
- Department of Physics, University of South Florida, Tampa, Florida.
| | - Angelo Demuro
- Department of Neurobiology and Behavior,University of California Irvine, Irvine, California.
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17
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Himschoot E, Pleskot R, Van Damme D, Vanneste S. The ins and outs of Ca 2+ in plant endomembrane trafficking. CURRENT OPINION IN PLANT BIOLOGY 2017; 40:131-137. [PMID: 28965016 DOI: 10.1016/j.pbi.2017.09.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Revised: 09/01/2017] [Accepted: 09/06/2017] [Indexed: 06/07/2023]
Abstract
Trafficking of proteins and lipids within the plant endomembrane system is essential to support cellular functions and is subject to rigorous regulation. Despite this seemingly strict regulation, endomembrane trafficking needs to be dynamically adjusted to ever-changing internal and environmental stimuli, while maintaining cellular integrity. Although often overlooked, the versatile second messenger Ca2+ is intimately connected to several endomembrane-associated processes. Here, we discuss the impact of electrostatic interactions between Ca2+ and anionic phospholipids on endomembrane trafficking, and illustrate the direct role of Ca2+ sensing proteins in regulating endomembrane trafficking and membrane integrity preservation. Moreover, we discuss how Ca2+ can control protein sorting within the plant endomembrane system. We thus highlight Ca2+ signaling as a versatile mechanism by which numerous signals are integrated into plant endomembrane trafficking dynamics.
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Affiliation(s)
- Ellie Himschoot
- Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Roman Pleskot
- Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, 9052 Ghent, Belgium; Institute of Experimental Botany, Czech Academy of Sciences, Rozvojova 263, 16502 Prague, Czech Republic
| | - Daniël Van Damme
- Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Steffen Vanneste
- Ghent University, Department of Plant Biotechnology and Bioinformatics, 9052 Ghent, Belgium; VIB Center for Plant Systems Biology, 9052 Ghent, Belgium.
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18
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Martin WE, Ge N, Srijanto BR, Furnish E, Collier CP, Trinkle CA, Richards CI. Real-Time Sensing of Single-Ligand Delivery with Nanoaperture-Integrated Microfluidic Devices. ACS OMEGA 2017; 2:3858-3867. [PMID: 28782052 PMCID: PMC5537690 DOI: 10.1021/acsomega.7b00934] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 07/11/2017] [Indexed: 05/28/2023]
Abstract
The measurement of biological events on the surface of live cells at the single-molecule level is complicated by several factors including high protein densities that are incompatible with single-molecule imaging, cellular autofluorescence, and protein mobility on the cell surface. Here, we fabricated a device composed of an array of nanoscale apertures coupled with a microfluidic delivery system to quantify single-ligand interactions with proteins on the cell surface. We cultured live cells directly on the device and isolated individual epidermal growth factor receptors (EGFRs) in the apertures while delivering fluorescently labeled epidermal growth factor. We observed single ligands binding to EGFRs, allowing us to quantify the ligand turnover in real time. These results demonstrate that this nanoaperture-coupled microfluidic device allows for the spatial isolation of individual membrane proteins while maintaining them in their cellular environment, providing the capability to monitor single-ligand binding events while maintaining receptors in their physiological environment. These methods should be applicable to a wide range of membrane proteins.
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Affiliation(s)
- W. Elliott Martin
- Department
of Chemistry, University of Kentucky, 505 Rose Street, Lexington, Kentucky 40506, United States
| | - Ning Ge
- Department
of Mechanical Engineering, University of
Kentucky, 151 Ralph G.
Anderson Building, Lexington, Kentucky 40506, United
States
| | - Bernadeta R. Srijanto
- Center
for Nanophase Materials Sciences, Oak Ridge
National Laboratory, Oak Ridge Tennessee 37831, United States
| | - Emily Furnish
- Department
of Chemistry, University of Kentucky, 505 Rose Street, Lexington, Kentucky 40506, United States
| | - C. Patrick Collier
- Center
for Nanophase Materials Sciences, Oak Ridge
National Laboratory, Oak Ridge Tennessee 37831, United States
| | - Christine A. Trinkle
- Department
of Mechanical Engineering, University of
Kentucky, 151 Ralph G.
Anderson Building, Lexington, Kentucky 40506, United
States
| | - Christopher I. Richards
- Department
of Chemistry, University of Kentucky, 505 Rose Street, Lexington, Kentucky 40506, United States
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19
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Petersen OH, Courjaret R, Machaca K. Ca 2+ tunnelling through the ER lumen as a mechanism for delivering Ca 2+ entering via store-operated Ca 2+ channels to specific target sites. J Physiol 2017; 595:2999-3014. [PMID: 28181236 PMCID: PMC5430212 DOI: 10.1113/jp272772] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/05/2017] [Indexed: 01/02/2023] Open
Abstract
Ca2+ signalling is perhaps the most universal and versatile mechanism regulating a wide range of cellular processes. Because of the many different calcium‐binding proteins distributed throughout cells, signalling precision requires localized rises in the cytosolic Ca2+ concentration. In electrically non‐excitable cells, for example epithelial cells, this is achieved by primary release of Ca2+ from the endoplasmic reticulum via Ca2+ release channels placed close to the physiological target. Because any rise in the cytosolic Ca2+ concentration activates Ca2+ extrusion, and in order for cells not to run out of Ca2+, there is a need for compensatory Ca2+ uptake from the extracellular fluid. This Ca2+ uptake occurs through a process known as store‐operated Ca2+ entry. Ideally Ca2+ entering the cell should not diffuse to the target site through the cytosol, as this would potentially activate undesirable processes. Ca2+ tunnelling through the lumen of the endoplasmic reticulum is a mechanism for delivering Ca2+ entering via store‐operated Ca2+ channels to specific target sites, and this process has been described in considerable detail in pancreatic acinar cells and oocytes. Here we review the most important evidence and present a generalized concept.
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Affiliation(s)
- Ole H Petersen
- MRC Group, School of Biosciences and Systems Immunity Research Institute, Cardiff University, Cardiff, CF10 3AX, UK
| | - Raphael Courjaret
- Department of Physiology and Biophysics, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, PO Box 24144, Doha, Qatar
| | - Khaled Machaca
- Department of Physiology and Biophysics, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, PO Box 24144, Doha, Qatar
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20
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Abstract
Total internal reflection fluorescence (TIRF) microscopy is a powerful tool for visualizing near-membrane cellular structures and processes, including imaging of local Ca2+ transients with single-channel resolution. TIRF is most commonly implemented in epi-fluorescence mode, whereby laser excitation light is introduced at a spot near the periphery of the back focal plane of a high numerical aperture objective lens. However, this approach results in an irregular illumination field, owing to interference fringes and scattering and shadowing by cellular structures. We describe a simple system to circumvent these limitations, utilizing a pair of galvanometer-driven mirrors to rapidly spin the laser spot in a circle at the back focal plane of the objective lens, so that irregularities average out during each camera exposure to produce an effectively uniform field. Computer control of the mirrors enables precise scanning at 200 Hz (5ms camera exposure times) or faster, and the scan radius can be altered on a frame-by-frame basis to achieve near-simultaneous imaging in TIRF, widefield and ‘skimming plane’ imaging modes. We demonstrate the utility of the system for dynamic recording of local inositol trisphosphate-mediated Ca2+ signals and for imaging the redistribution of STIM and Orai proteins during store-operated Ca2+ entry. We further anticipate that it will be readily applicable for numerous other near-membrane studies, especially those involving fast dynamic processes.
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21
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Weinberg SH, Smith GD. The influence of Ca²⁺ buffers on free [Ca²⁺] fluctuations and the effective volume of Ca²⁺ microdomains. Biophys J 2015; 106:2693-709. [PMID: 24940787 DOI: 10.1016/j.bpj.2014.04.045] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 04/28/2014] [Accepted: 04/30/2014] [Indexed: 02/06/2023] Open
Abstract
Intracellular calcium (Ca(2+)) plays a significant role in many cell signaling pathways, some of which are localized to spatially restricted microdomains. Ca(2+) binding proteins (Ca(2+) buffers) play an important role in regulating Ca(2+) concentration ([Ca(2+)]). Buffers typically slow [Ca(2+)] temporal dynamics and increase the effective volume of Ca(2+) domains. Because fluctuations in [Ca(2+)] decrease in proportion to the square-root of a domain's physical volume, one might conjecture that buffers decrease [Ca(2+)] fluctuations and, consequently, mitigate the significance of small domain volume concerning Ca(2+) signaling. We test this hypothesis through mathematical and computational analysis of idealized buffer-containing domains and their stochastic dynamics during free Ca(2+) influx with passive exchange of both Ca(2+) and buffer with bulk concentrations. We derive Langevin equations for the fluctuating dynamics of Ca(2+) and buffer and use these stochastic differential equations to determine the magnitude of [Ca(2+)] fluctuations for different buffer parameters (e.g., dissociation constant and concentration). In marked contrast to expectations based on a naive application of the principle of effective volume as employed in deterministic models of Ca(2+) signaling, we find that mobile and rapid buffers typically increase the magnitude of domain [Ca(2+)] fluctuations during periods of Ca(2+) influx, whereas stationary (immobile) Ca(2+) buffers do not. Also contrary to expectations, we find that in the absence of Ca(2+) influx, buffers influence the temporal characteristics, but not the magnitude, of [Ca(2+)] fluctuations. We derive an analytical formula describing the influence of rapid Ca(2+) buffers on [Ca(2+)] fluctuations and, importantly, identify the stochastic analog of (deterministic) effective domain volume. Our results demonstrate that Ca(2+) buffers alter the dynamics of [Ca(2+)] fluctuations in a nonintuitive manner. The finding that Ca(2+) buffers do not suppress intrinsic domain [Ca(2+)] fluctuations raises the intriguing question of whether or not [Ca(2+)] fluctuations are a physiologically significant aspect of local Ca(2+) signaling.
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Affiliation(s)
- Seth H Weinberg
- Department of Applied Science, The College of William & Mary, Williamsburg, Virginia
| | - Gregory D Smith
- Department of Applied Science, The College of William & Mary, Williamsburg, Virginia.
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22
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Weatherill EE, Wallace MI. Combining Single-Molecule Imaging and Single-Channel Electrophysiology. J Mol Biol 2015; 427:146-57. [DOI: 10.1016/j.jmb.2014.07.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 12/29/2022]
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23
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Sasmal D, Lu HP. Single-molecule patch-clamp FRET microscopy studies of NMDA receptor ion channel dynamics in living cells: revealing the multiple conformational states associated with a channel at its electrical off state. J Am Chem Soc 2014; 136:12998-3005. [PMID: 25148304 PMCID: PMC4183623 DOI: 10.1021/ja506231j] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Indexed: 01/10/2023]
Abstract
Conformational dynamics plays a critical role in the activation, deactivation, and open-close activities of ion channels in living cells. Such conformational dynamics is often inhomogeneous and extremely difficult to be directly characterized by ensemble-averaged spectroscopic imaging or only by single channel patch-clamp electric recording methods. We have developed a new and combined technical approach, single-molecule patch-clamp FRET microscopy, to probe ion channel conformational dynamics in living cell by simultaneous and correlated measurements of real-time single-molecule FRET spectroscopic imaging with single-channel electric current recording. Our approach is particularly capable of resolving ion channel conformational change rate process when the channel is at its electrically off states and before the ion channel is activated, the so-called "silent time" when the electric current signals are at zero or background. We have probed NMDA (N-methyl-D-aspartate) receptor ion channel in live HEK-293 cell, especially, the single ion channel open-close activity and its associated protein conformational changes simultaneously. Furthermore, we have revealed that the seemingly identical electrically off states are associated with multiple conformational states. On the basis of our experimental results, we have proposed a multistate clamshell model to interpret the NMDA receptor open-close dynamics.
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Affiliation(s)
- Dibyendu
Kumar Sasmal
- Department
of Chemistry and
Center for Photochemical Sciences, Bowling
Green State University, Bowling
Green, Ohio 43403, United States
| | - H. Peter Lu
- Department
of Chemistry and
Center for Photochemical Sciences, Bowling
Green State University, Bowling
Green, Ohio 43403, United States
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24
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Mid-range Ca2+ signalling mediated by functional coupling between store-operated Ca2+ entry and IP3-dependent Ca2+ release. Nat Commun 2014; 5:3916. [PMID: 24867608 DOI: 10.1038/ncomms4916] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 04/17/2014] [Indexed: 11/08/2022] Open
Abstract
The versatility and universality of Ca(2+) signals stem from the breadth of their spatial and temporal dynamics. Spatially, Ca(2+) signalling is well studied in the microdomain scale, close to a Ca(2+) channel, and at the whole-cell level. However, little is known about how local Ca(2+) signals are regulated to specifically activate spatially distant effectors without a global Ca(2+) rise. Here we show that an intricate coupling between the inositol 1,4,5 trisphosphate (IP3) receptor, SERCA pump and store-operated Ca(2+) entry (SOCE) allows for efficient mid-range Ca(2+) signalling. Ca(2+) flowing through SOCE is taken up into the ER lumen by the SERCA pump, only to be re-released by IP3Rs to activate distal Ca(2+)-activated Cl(-) channels (CaCCs). This CaCC regulation contributes to setting the membrane potential of the cell. Hence functional coupling between SOCE, SERCA and IP3R limits local Ca(2+) diffusion and funnels Ca(2+) through the ER lumen to activate a spatially separate Ca(2+) effector.
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25
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van Bel AJE, Furch ACU, Will T, Buxa SV, Musetti R, Hafke JB. Spread the news: systemic dissemination and local impact of Ca²⁺ signals along the phloem pathway. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1761-87. [PMID: 24482370 DOI: 10.1093/jxb/ert425] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We explored the idea of whether electropotential waves (EPWs) primarily act as vehicles for systemic spread of Ca(2+) signals. EPW-associated Ca(2+) influx may trigger generation and amplification of countless long-distance signals along the phloem pathway given the fact that gating of Ca(2+)-permeable channels is a universal response to biotic and abiotic challenges. Despite fundamental differences, both action and variation potentials are associated with a sudden Ca(2+) influx. Both EPWs probably disperse in the lateral direction, which could be of essential functional significance. A vast set of Ca(2+)-permeable channels, some of which have been localized, is required for Ca(2+)-modulated events in sieve elements. There, Ca(2+)-permeable channels are clustered and create so-called Ca(2+) hotspots, which play a pivotal role in sieve element occlusion. Occlusion mechanisms play a central part in the interaction between plants and phytopathogens (e.g. aphids or phytoplasmas) and in transient re-organization of the vascular symplasm. It is argued that Ca(2+)-triggered systemic signalling occurs in partly overlapping waves. The forefront of EPWs may be accompanied by a burst of free Ca(2+) ions and Ca(2+)-binding proteins in the sieve tube sap, with a far-reaching impact on target cells. Lateral dispersion of EPWs may induce diverse Ca(2+) influx and handling patterns (Ca(2+) signatures) in various cell types lining the sieve tubes. As a result, a variety of cascades may trigger the fabrication of signals such as phytohormones, proteins, or RNA species released into the sap stream after product-related lag times. Moreover, transient reorganization of the vascular symplasm could modify cascades in disjunct vascular cells.
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Affiliation(s)
- Aart J E van Bel
- Institute of General Botany, Justus-Liebig University, Senckenbergstrasse 17, D-35390 Giessen, Germany
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26
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Cantero MDR, Cantiello HF. Calcium transport and local pool regulate polycystin-2 (TRPP2) function in human syncytiotrophoblast. Biophys J 2014; 105:365-75. [PMID: 23870258 DOI: 10.1016/j.bpj.2013.05.058] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 05/16/2013] [Accepted: 05/30/2013] [Indexed: 01/26/2023] Open
Abstract
Polycystin-2 (PC2, TRPP2) is a Ca(2+)-permeable, nonselective cation channel implicated in Ca(2+) transport and epithelial cell signaling. Although PC2 may contribute to Ca(2+) transport in human term placenta, the regulatory mechanisms associated with Ca(2+) handling in this tissue are largely unknown. In this work we assessed the regulation by Ca(2+) of PC2 channel function from a preparation of apical membranes of human syncytiotrophoblast (PC2hst) reconstituted in a lipid bilayer system. Addition of either EGTA or BAPTA to the cis hemi-chamber, representing the cytoplasmic domain of the channel, and lowering Ca(2+) to ∼0.6-0.8 nM, inhibited spontaneous PC2hst channel activity, with a time response dependent on the chelator tested. EGTA reduced PC2hst channel currents by 86%, with a t1/2 = 3.6 min, whereas BAPTA rapidly and completely (100%) eliminated channel activity with a t1/2 = 0.8 min. Subsequent titration with Ca(2+) reversed the inhibition, which followed a Hill-type function with apparent dissociation constants of 1-5 nM, and 4 Ca(2+) binding sites. The degree of inhibition by the cis Ca(2+) chelator largely depended on increasing trans Ca(2+). This was consistent with measurable Ca(2+) transport through the channel, feeding the regulatory sites in the cytoplasmic domain. Interestingly, the reconstituted in vitro translated PC2 (PC2iv) was completely insensitive to Ca(2+) regulation, suggesting that the regulatory sites are not intrinsic to the channel protein. Our findings demonstrate the presence of a Ca(2+) microdomain largely accessible through the channel that controls PC2 function in human syncytiotrophoblast of term placenta.
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Affiliation(s)
- María Del Rocío Cantero
- Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, Buenos Aires, Argentina
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27
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Actin-based confinement of calcium responses during Shigella invasion. Nat Commun 2013; 4:1567. [DOI: 10.1038/ncomms2561] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Accepted: 01/28/2013] [Indexed: 12/18/2022] Open
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28
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Lin-Moshier Y, Marchant JS. The Xenopus oocyte: a single-cell model for studying Ca2+ signaling. Cold Spring Harb Protoc 2013; 2013:2013/3/pdb.top066308. [PMID: 23457336 DOI: 10.1101/pdb.top066308] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In the four decades since the Xenopus oocyte was first demonstrated to have the capacity to translate exogenous mRNAs, this system has been exploited for many different experimental purposes. Typically, the oocyte is used either as a "biological test tube" for heterologous expression of proteins without any particular cell biological insight or, alternatively, it is used for applications where cell biology is paramount, such as investigations of the cellular adaptations that power early development. In this article, we discuss the utility of the Xenopus oocyte for studying Ca(2+) signaling in both these contexts.
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Affiliation(s)
- Yaping Lin-Moshier
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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29
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Calcium as a Trigger and Regulator of Systemic Alarms and Signals along the Phloem Pathway. LONG-DISTANCE SYSTEMIC SIGNALING AND COMMUNICATION IN PLANTS 2013. [DOI: 10.1007/978-3-642-36470-9_18] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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30
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Abstract
Ion channels, as membrane proteins, are the sensors of the cell. They act as the first line of communication with the world beyond the plasma membrane and transduce changes in the external and internal environments into unique electrical signals to shape the responses of excitable cells. Because of their importance in cellular communication, ion channels have been intensively studied at the structural and functional levels. Here, we summarize the diverse approaches, including molecular and cellular, chemical, optical, biophysical, and computational, used to probe the structural and functional rearrangements that occur during channel activation (or sensitization), inactivation (or desensitization), and various forms of modulation. The emerging insights into the structure and function of ion channels by multidisciplinary approaches allow the development of new pharmacotherapies as well as new tools useful in controlling cellular activity.
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Affiliation(s)
- Wei-Guang Li
- Neuroscience Division, Department of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
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31
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Sullivan MN, Francis M, Pitts NL, Taylor MS, Earley S. Optical recording reveals novel properties of GSK1016790A-induced vanilloid transient receptor potential channel TRPV4 activity in primary human endothelial cells. Mol Pharmacol 2012; 82:464-72. [PMID: 22689561 DOI: 10.1124/mol.112.078584] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Critical functions of the vascular endothelium are regulated by changes in intracellular [Ca(2+)]. Endothelial dysfunction is tightly associated with cardiovascular disease, and improved understanding of Ca(2+) entry pathways in these cells will have a significant impact on human health. However, much about Ca(2+) influx channels in endothelial cells remains unknown because they are difficult to study using conventional patch-clamp electrophysiology. Here we describe a novel, highly efficient method for recording and analyzing Ca(2+)-permeable channel activity in primary human endothelial cells using a unique combination of total internal reflection fluorescence microscopy (TIRFM), custom software-based detection, and selective pharmacology. Our findings indicate that activity of the vanilloid (V) transient receptor potential (TRP) channel TRPV4 can be rapidly recorded and characterized at the single-channel level using this method, providing novel insight into channel function. Using this method, we show that although TRPV4 protein is evenly distributed throughout the plasma membrane, most channels are silent even during maximal stimulation with the potent TRPV4 agonist N-((1S)-1-{[4-((2S)-2-{[(2,4-dichlorophenyl)sulfonyl]amino}-3-hydroxypropanoyl)-1-piperazinyl]carbonyl}-3-methylbutyl)-1-benzothiophene-2-carboxamide (GSK1016790A). Furthermore, our findings indicate that GSK1016790A acts by recruiting previously inactive channels, rather than through increasing elevation of basal activity.
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Affiliation(s)
- Michelle N Sullivan
- Vascular Physiology Research Group, Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado 80523-1680, USA
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32
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Nanodomain Ca²⁺ of Ca²⁺ channels detected by a tethered genetically encoded Ca²⁺ sensor. Nat Commun 2012; 3:778. [PMID: 22491326 PMCID: PMC3615648 DOI: 10.1038/ncomms1777] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 03/07/2012] [Indexed: 12/29/2022] Open
Abstract
Coupling of excitation to secretion, contraction and transcription often relies on Ca(2+) computations within the nanodomain-a conceptual region extending tens of nanometers from the cytoplasmic mouth of Ca(2+) channels. Theory predicts that nanodomain Ca(2+) signals differ vastly from the slow submicromolar signals routinely observed in bulk cytoplasm. However, direct visualization of nanodomain Ca(2+) far exceeds optical resolution of spatially distributed Ca(2+) indicators. Here we couple an optical, genetically encoded Ca(2+) indicator (TN-XL) to the carboxy tail of Ca(V)2.2 Ca(2+) channels, enabling near-field imaging of the nanodomain. Under total internal reflection fluorescence microscopy, we detect Ca(2+) responses indicative of large-amplitude pulses. Single-channel electrophysiology reveals a corresponding Ca(2+) influx of only 0.085 pA, and fluorescence resonance energy transfer measurements estimate TN-XL distance to the cytoplasmic mouth at ~55 Å. Altogether, these findings raise the possibility that Ca(2+) exits the channel through the analogue of molecular portals, mirroring the crystallographic images of side windows in voltage-gated K channels.
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33
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Kim E, Shino S, Yoon J, Leung HT. In search of proteins that are important for synaptic functions in Drosophila visual system. J Neurogenet 2012; 26:151-7. [PMID: 22283835 DOI: 10.3109/01677063.2011.648290] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
This is the second of two reviews that include some of the studies we, members of the Pak laboratory and collaborators, did from 2000 to 2010 on the mutants that affect synaptic transmission in the Drosophila visual system. Of the five mutants we discuss, two turned out to also play roles in the larval neuromuscular junction. This review complements the one on phototransduction to give a fairly complete account of what we focused on during the 10-year period, although we also did some studies on photoreceptor degeneration in the early part of the decade. Besides showing the power of using a genetic approach to the study of synaptic transmission, the review contains some unexpected results that illustrate the serendipitous nature of research.
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Affiliation(s)
- Eunju Kim
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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34
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Li X, Li PCH. Strategies for the real-time detection of Ca2+ channel events of single cells: recent advances and new possibilities. Expert Rev Clin Pharmacol 2012; 3:267-80. [PMID: 22111609 DOI: 10.1586/ecp.10.16] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Ca(2+) ion channels play key roles in cell physiology and they are important drug targets. The Ca(2+) channel events are mainly measurable by fluorescent and patch clamp methods. This review summarizes the recent advances of these techniques for the detection of Ca(2+) channel events and the prospect of their new directions in the near future. Conventional bulk fluorescent methods are amenable to high-throughput applications, but they are not real-time single-cell measurements, which provide kinetic data on individual cells and offer unparalleled sensitive data for rare cells. Recent advances on real-time single-cell fluorescent measurements are conducted on microfluidic chips with scalable cell-retention sites, integrated with electrical stimulation and fluorescent measuring features. Patch clamp techniques are real-time measurements conducted on single cells, but the measurements are of low throughput. Recent advances are conducted on microfluidic patch clamp chips for high-throughput applications. Future real-time single-cell Ca(2+) channel event measurements will be conducted in a multiparametric manner in an integrated and automated microfluidic chip.
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Affiliation(s)
- XiuJun Li
- University of California at Berkeley, CA 94720, USA
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35
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36
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Vizcay-Barrena G, Webb SED, Martin-Fernandez ML, Wilson ZA. Subcellular and single-molecule imaging of plant fluorescent proteins using total internal reflection fluorescence microscopy (TIRFM). JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:5419-28. [PMID: 21865179 PMCID: PMC3223039 DOI: 10.1093/jxb/err212] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2011] [Revised: 06/08/2011] [Accepted: 06/10/2011] [Indexed: 05/18/2023]
Abstract
Total internal reflection fluorescence microscopy (TIRFM) has been proven to be an extremely powerful technique in animal cell research for generating high contrast images and dynamic protein conformation information. However, there has long been a perception that TIRFM is not feasible in plant cells because the cell wall would restrict the penetration of the evanescent field and lead to scattering of illumination. By comparative analysis of epifluorescence and TIRF in root cells, it is demonstrated that TIRFM can generate high contrast images, superior to other approaches, from intact plant cells. It is also shown that TIRF imaging is possible not only at the plasma membrane level, but also in organelles, for example the nucleus, due to the presence of the central vacuole. Importantly, it is demonstrated for the first time that this is TIRF excitation, and not TIRF-like excitation described as variable-angle epifluorescence microscopy (VAEM), and it is shown how to distinguish the two techniques in practical microscopy. These TIRF images show the highest signal-to-background ratio, and it is demonstrated that they can be used for single-molecule microscopy. Rare protein events, which would otherwise be masked by the average molecular behaviour, can therefore be detected, including the conformations and oligomerization states of interacting proteins and signalling networks in vivo. The demonstration of the application of TIRFM and single-molecule analysis to plant cells therefore opens up a new range of possibilities for plant cell imaging.
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Affiliation(s)
- Gema Vizcay-Barrena
- School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
| | - Stephen E. D. Webb
- Science and Technology Facilities Council, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK
| | - Marisa L. Martin-Fernandez
- Science and Technology Facilities Council, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK
| | - Zoe A. Wilson
- School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
- To whom correspondence should be addressed. E-mail:
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37
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Demuro A, Smith M, Parker I. Single-channel Ca(2+) imaging implicates Aβ1-42 amyloid pores in Alzheimer's disease pathology. ACTA ACUST UNITED AC 2011; 195:515-24. [PMID: 22024165 PMCID: PMC3206345 DOI: 10.1083/jcb.201104133] [Citation(s) in RCA: 138] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
High-resolution imaging of calcium influx reveals that the Aβ peptides implicated in Alzheimer’s disease form highly toxic Ca2+-permeable pores. Oligomeric forms of Aβ peptides are implicated in Alzheimer’s disease (AD) and disrupt membrane integrity, leading to cytosolic calcium (Ca2+) elevation. Proposed mechanisms by which Aβ mediates its effects include lipid destabilization, activation of native membrane channels, and aggregation of Aβ into Ca2+-permeable pores. We distinguished between these using total internal reflection fluorescence (TIRF) microscopy to image Ca2+ influx in Xenopus laevis oocytes. Aβ1–42 oligomers evoked single-channel Ca2+ fluorescence transients (SCCaFTs), which resembled those from classical ion channels but which were not attributable to endogenous oocyte channels. SCCaFTs displayed widely variable open probabilities (Po) and stepwise transitions among multiple amplitude levels reminiscent of subconductance levels of ion channels. The proportion of high Po, large amplitude SCCaFTs grew with time, suggesting that continued oligomer aggregation results in the formation of highly toxic pores. We conclude that formation of intrinsic Ca2+-permeable membrane pores is a major pathological mechanism in AD and introduce TIRF imaging for massively parallel single-channel studies of the incorporation, assembly, and properties of amyloidogenic oligomers.
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Affiliation(s)
- Angelo Demuro
- Department of Neurobiology and Behavior, University of California, Irvine, Irvine, CA 92697, USA.
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Rossi AM, Tovey SC, Rahman T, Prole DL, Taylor CW. Analysis of IP3 receptors in and out of cells. Biochim Biophys Acta Gen Subj 2011; 1820:1214-27. [PMID: 22033379 DOI: 10.1016/j.bbagen.2011.10.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 10/07/2011] [Accepted: 10/08/2011] [Indexed: 10/16/2022]
Abstract
BACKGROUND Inositol 1,4,5-trisphosphate receptors (IP3R) are expressed in almost all animal cells. Three mammalian genes encode closely related IP3R subunits, which assemble into homo- or hetero-tetramers to form intracellular Ca2+ channels. SCOPE OF THE REVIEW In this brief review, we first consider a variety of complementary methods that allow the links between IP3 binding and channel gating to be defined. How does IP3 binding to the IP3-binding core in each IP3R subunit cause opening of a cation-selective pore formed by residues towards the C-terminal? We then describe methods that allow IP3, Ca2+ signals and IP3R mobility to be examined in intact cells. A final section briefly considers genetic analyses of IP3R signalling. MAJOR CONCLUSIONS All IP3R are regulated by both IP3 and Ca2+. This allows them to initiate and regeneratively propagate intracellular Ca2+ signals. The elementary Ca2+ release events evoked by IP3 in intact cells are mediated by very small numbers of active IP3R and the Ca2+-mediated interactions between them. The spatial organization of these Ca2+ signals and their stochastic dependence on so few IP3Rs highlight the need for methods that allow the spatial organization of IP3R signalling to be addressed with single-molecule resolution. GENERAL SIGNIFICANCE A variety of complementary methods provide insight into the structural basis of IP3R activation and the contributions of IP3-evoked Ca2+ signals to cellular physiology. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
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Ribrault C, Sekimoto K, Triller A. From the stochasticity of molecular processes to the variability of synaptic transmission. Nat Rev Neurosci 2011; 12:375-87. [PMID: 21685931 DOI: 10.1038/nrn3025] [Citation(s) in RCA: 146] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The variability of the postsynaptic response following a single action potential arises from two sources: the neurotransmitter release is probabilistic, and the postsynaptic response to neurotransmitter release has variable timing and amplitude. At individual synapses, the number of molecules of a given type that are involved in these processes is small enough that the stochastic (random) properties of molecular events cannot be neglected. How the stochasticity of molecular processes contributes to the variability of synaptic transmission, its sensitivity and its robustness to molecular fluctuations has important implications for our understanding of the mechanistic basis of synaptic transmission and of synaptic plasticity.
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Affiliation(s)
- Claire Ribrault
- Laboratoire Matières et Systèmes Complexes, CNRS-UMR7057, Université Paris 7, F-75205 Paris cedex 13, France
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40
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Superresolution localization of single functional IP3R channels utilizing Ca2+ flux as a readout. Biophys J 2010; 99:437-46. [PMID: 20643061 DOI: 10.1016/j.bpj.2010.04.037] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Revised: 04/06/2010] [Accepted: 04/14/2010] [Indexed: 11/22/2022] Open
Abstract
The subcellular localization of membrane Ca2+ channels is crucial for their functioning, but is difficult to study because channels may be distributed more closely than the resolution of conventional microscopy is able to detect. We describe a technique, stochastic channel Ca2+ nanoscale resolution (SCCaNR), employing Ca2+-sensitive fluorescent dyes to localize stochastic openings and closings of single Ca2+-permeable channels within <50 nm, and apply it to examine the clustered arrangement of inositol trisphosphate receptor (IP3R) channels underlying local Ca2+ puffs. Fluorescence signals (blips) arising from single functional IP3Rs are almost immotile (diffusion coefficient<0.003 microm2 s(-1)), as are puff sites over prolonged periods, suggesting that the architecture of this signaling system is stable and not subject to rapid, dynamic rearrangement. However, rapid stepwise changes in centroid position of fluorescence are evident within the durations of individual puffs. These apparent movements likely result from asynchronous gating of IP3Rs distributed within clusters that have an overall diameter of approximately 400 nm, indicating that the nanoscale architecture of IP3R clusters is important in shaping local Ca2+ signals. We anticipate that SCCaNR will complement superresolution techniques such as PALM and STORM for studies of Ca2+ channels as it obviates the need for photoswitchable labels and provides functional as well as spatial information.
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Castillo K, Restrepo D, Bacigalupo J. Cellular and molecular Ca2+ microdomains in olfactory cilia support low signaling amplification of odor transduction. Eur J Neurosci 2010; 32:932-8. [PMID: 20849528 DOI: 10.1111/j.1460-9568.2010.07393.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Signal transduction depends critically on the spatial localization of protein constituents. A key question in odor transduction is whether chemotransduction proteins organize into discrete molecular complexes throughout olfactory cilia or distribute homogeneously along the ciliary membrane. Our recordings of Ca(2+) changes in individual cilia with unprecedented spatial and temporal resolution, by the use of two-photon microscopy, provide solid evidence for Ca(2+) microdomains (transducisomes). Dissociated frog olfactory neurons were preloaded with caged-cAMP and fluo-4 acetoxymethyl ester probe Ca(2+) indicator. Ca(2+) influx through cyclic nucleotide-gated (CNG) channels was evoked by uniformly photoreleasing cAMP, while ciliary Ca(2+) was measured. Discrete fluorescence events were clearly resolved. Events were missing in the absence of external Ca(2+) , consistent with the absence of internal Ca(2+) sources. Fluorescence events at individual microdomains resembled single-CNG channel fluctuations in shape, mean duration and kinetics, indicating that transducisomes typically contain one to three CNG channels. Inhibiting the Na(+) /Ca(2+) exchanger or the Ca(2+) -ATPase prolonged the decay of evoked intraciliary Ca(2+) transients, supporting the participation of both transporters in ciliary Ca(2+) clearance, and suggesting that both molecules localize close to the CNG channel. Chemosensory transducisomes provide a physical basis for the low amplification and for the linearity of odor responses at low odor concentrations.
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Affiliation(s)
- Karen Castillo
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Las Palmeras 3525, Nuñoa, Santiago 7800024
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42
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Essential regulation of cell bioenergetics by constitutive InsP3 receptor Ca2+ transfer to mitochondria. Cell 2010; 142:270-83. [PMID: 20655468 DOI: 10.1016/j.cell.2010.06.007] [Citation(s) in RCA: 808] [Impact Index Per Article: 57.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Revised: 03/26/2010] [Accepted: 05/20/2010] [Indexed: 01/26/2023]
Abstract
Mechanisms that regulate cellular metabolism are a fundamental requirement of all cells. Most eukaryotic cells rely on aerobic mitochondrial metabolism to generate ATP. Nevertheless, regulation of mitochondrial activity is incompletely understood. Here we identified an unexpected and essential role for constitutive InsP(3)R-mediated Ca(2+) release in maintaining cellular bioenergetics. Macroautophagy provides eukaryotes with an adaptive response to nutrient deprivation that prolongs survival. Constitutive InsP(3)R Ca(2+) signaling is required for macroautophagy suppression in cells in nutrient-replete media. In its absence, cells become metabolically compromised due to diminished mitochondrial Ca(2+) uptake. Mitochondrial uptake of InsP(3)R-released Ca(2+) is fundamentally required to provide optimal bioenergetics by providing sufficient reducing equivalents to support oxidative phosphorylation. Absence of this Ca(2+) transfer results in enhanced phosphorylation of pyruvate dehydrogenase and activation of AMPK, which activates prosurvival macroautophagy. Thus, constitutive InsP(3)R Ca(2+) release to mitochondria is an essential cellular process that is required for efficient mitochondrial respiration and maintenance of normal cell bioenergetics.
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43
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Parker I, Smith IF. Recording single-channel activity of inositol trisphosphate receptors in intact cells with a microscope, not a patch clamp. J Gen Physiol 2010; 136:119-27. [PMID: 20660654 PMCID: PMC2912063 DOI: 10.1085/jgp.200910390] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Optical single-channel recording is a novel tool for the study of individual Ca2+-permeable channels within intact cells under minimally perturbed physiological conditions. As applied to the functioning and spatial organization of IP3Rs, this approach complements our existing knowledge, which derives largely from reduced systems - such as reconstitution into lipid bilayers and patch clamping of IP3Rs on the membrane of excised nuclei - where the spatial arrangement and interactions among IP3Rs via CICR are disrupted. The ability to image the activity of single IP3R channels with millisecond resolution together with localization of their positions with a precision of a few tens of nanometers both raises several intriguing questions and holds promise of answers. In particular, what mechanism underlies the anchoring of puffs and blips to static locations; why do these Ca2+ release events appear to involve only a very small fraction of the IP3Rs within a cell; and how can we reconcile the relative immotility of functional IP3Rs with numerous studies reporting free diffusion of IP3R protein in the ER membrane?
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Affiliation(s)
- Ian Parker
- Department of Neurobiology and Behavior, and Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697
| | - Ian F. Smith
- Department of Neurobiology and Behavior, and Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697
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44
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Elson EC. Complex life forms may arise from electrical processes. Theor Biol Med Model 2010; 7:26. [PMID: 20576122 PMCID: PMC2908058 DOI: 10.1186/1742-4682-7-26] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Accepted: 06/24/2010] [Indexed: 11/21/2022] Open
Abstract
There is still not an appealing and testable model to explain how single-celled organisms, usually following fusion of male and female gametes, proceed to grow and evolve into multi-cellular, complexly differentiated systems, a particular species following virtually an invariant and unique growth pattern. An intrinsic electrical oscillator, resembling the cardiac pacemaker, may explain the process. Highly auto-correlated, it could live independently of ordinary thermodynamic processes which mandate increasing disorder, and could coordinate growth and differentiation of organ anlage.
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Affiliation(s)
- Edward C Elson
- Department of Electrical and Computer Engineering, University of Maryland, College Park, College Park, Maryland 20742, USA.
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45
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Ait-Haddou R, Kurachi Y, Nomura T. On calcium–buffer dynamics within the excess buffer regime. J Theor Biol 2010; 264:55-65. [DOI: 10.1016/j.jtbi.2010.01.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Revised: 01/04/2010] [Accepted: 01/15/2010] [Indexed: 10/19/2022]
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46
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Vacuolar ion channels: Roles in plant nutrition and signalling. FEBS Lett 2010; 584:1982-8. [DOI: 10.1016/j.febslet.2010.02.050] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 02/17/2010] [Accepted: 02/18/2010] [Indexed: 11/19/2022]
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47
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Toescu EC, Graham J. Ca2+ Recordings: Hardware and Software (From Microscopes to Cameras). NEUROMETHODS 2010. [DOI: 10.1007/978-1-60761-476-0_2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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48
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Wu MM, Llobet A, Lagnado L. Loose coupling between calcium channels and sites of exocytosis in chromaffin cells. J Physiol 2009; 587:5377-91. [PMID: 19752110 DOI: 10.1113/jphysiol.2009.176065] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Calcium microdomains generated by tight clusters of calcium channels regulate fusion of small vesicles at the synaptic terminal and have also been suggested to trigger exocytosis of large dense-core vesicles from neuroendocrine cells. To test this idea, we have compared sites of exocytosis and the spatial distribution of calcium channels in chromaffin cells. Fusion of individual vesicles was visualized using interference reflection microscopy and the submembranous calcium signal was assessed using total internal reflection fluorescence microscopy. Depolarization triggered a burst of exocytosis from up to seven sites in a membrane area of 11 microm(2), but these sites did not colocalize with calcium microdomains. Instead, calcium influx occurred in large patches (averaging 34 microm(2)) containing a mixture of P/Q- and N-type channels. About 20% of fusion events occurred outside calcium channel patches. Further, the delay between the onset of stimulation and a burst of exocytosis was prolonged for several seconds by increasing the concentration of the slow calcium chelator EGTA from 1.5 to 5 mM. These results demonstrate that while calcium channels and release sites tend to congregate in specialized regions of the surface membrane, these have dimensions of several micrometres. The dominant calcium signal regulating release in chromaffin cells is generated by the cooperative action of many channels operating over distances of many micrometres rather than discrete clusters of calcium channels generating localized microdomains.
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Affiliation(s)
- Minnie M Wu
- MRC Laboratory of Molecular Biology, Cambridge, UK
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49
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Furch ACU, van Bel AJE, Fricker MD, Felle HH, Fuchs M, Hafke JB. Sieve element Ca2+ channels as relay stations between remote stimuli and sieve tube occlusion in Vicia faba. THE PLANT CELL 2009; 21:2118-32. [PMID: 19602624 PMCID: PMC2729599 DOI: 10.1105/tpc.108.063107] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Damage induces remote occlusion of sieve tubes in Vicia faba by forisome dispersion, triggered during the passage of an electropotential wave (EPW). This study addresses the role of Ca2+ channels and cytosolic Ca2+ elevation as a link between EPWs and forisome dispersion. Ca2+ channel antagonists affect the initial phase of the EPW as well as the prolonged plateau phase. Resting levels of sieve tube Ca2+ of approximately 50 nM were independently estimated using Ca2+-selective electrodes and a Ca2+-sensitive dye. Transient changes in cytosolic Ca2+ were observed in phloem tissue in response to remote stimuli and showed profiles similar to those of EPWs. The measured elevation of Ca2+ in sieve tubes was below the threshold necessary for forisome dispersion. Therefore, forisomes need to be associated with Ca2+ release sites. We found an association between forisomes and endoplasmic reticulum (ER) at sieve plates and pore-plasmodesma units where high-affinity binding of a fluorescent Ca2+ channel blocker mapped an increased density of Ca2+ channels. In conclusion, propagation of EPWs in response to remote stimuli is linked to forisome dispersion through transiently high levels of parietal Ca2+, release of which depends on both plasma membrane and ER Ca2+ channels.
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Affiliation(s)
- Alexandra C U Furch
- Plant Cell Biology Research Group, Institute of General Botany, Justus-Liebig-University, D-35390 Giessen, Germany
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50
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Abstract
Advances in microscopy and fluorescent probes provide new insight into the nanometer-scale biochemistry governing the interactions between eukaryotic cells and pathogens. When combined with mathematical modelling, these new technologies hold the promise of qualitative, quantitative and predictive descriptions of these pathways. Using the light microscope to study the spatial and temporal relationships between pathogens, host cells and their respective biochemical machinery requires an appreciation for how fluorescent probes and imaging devices function. This review summarizes how live cell fluorescence microscopy with common instruments can provide quantitative insight into the cellular and molecular functions of hosts and pathogens.
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Affiliation(s)
- Adam D Hoppe
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007-0896, USA.
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