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Canepari M, Ross WN. Spatial and temporal aspects of neuronal calcium and sodium signals measured with low-affinity fluorescent indicators. Pflugers Arch 2024; 476:39-48. [PMID: 37798555 DOI: 10.1007/s00424-023-02865-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 09/12/2023] [Accepted: 09/21/2023] [Indexed: 10/07/2023]
Abstract
Low-affinity fluorescent indicators for Ca2+ or Na+ allow measuring the dynamics of intracellular concentration of these ions with little perturbation from physiological conditions because they are weak buffers. When using synthetic indicators, which are small molecules with fast kinetics, it is also possible to extract spatial and temporal information on the sources of ion transients, their localization, and their disposition. This review examines these important aspects from the biophysical point of view, and how they have been recently exploited in neurophysiological studies. We first analyze the environment where Ca2+ and Na+ indicators are inserted, highlighting the interpretation of the two different signals. Then, we address the information that can be obtained by analyzing the rising phase and the falling phase of the Ca2+ and Na+ transients evoked by different stimuli, focusing on the kinetics of ionic currents and on the spatial interpretation of these measurements, especially on events in axons and dendritic spines. Finally, we suggest how Ca2+ or Na+ imaging using low-affinity synthetic fluorescent indicators can be exploited in future fundamental or applied research.
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Affiliation(s)
- Marco Canepari
- LIPhy, CNRS, Univ. Grenoble Alpes, F-38000, Grenoble, France.
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France.
- Institut National de la Santé et Recherche Médicale, Paris, France.
| | - William N Ross
- Department of Physiology, New York Medical College, Valhalla, NY, 10595, USA
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2
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Metwally K, Abo-Dya NE, Hamdan AME, Alrashidi MN, Alturki MS, Aly OM, Aljoundi A, Ibrahim M, Soliman MES. Investigation of Simultaneous and Sequential Cooperative Homotropic Inhibitor Binding to the Catalytic Chamber of SARS-CoV-2 RNA-dependent RNA Polymerase (RdRp). Cell Biochem Biophys 2023; 81:697-706. [PMID: 37658974 DOI: 10.1007/s12013-023-01163-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/05/2023] [Indexed: 09/05/2023]
Abstract
In our previous report, the unique architecture of the catalytic chamber of the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp), which harbours two distinctive binding sites, was fully characterized at molecular level. The significant differences in the two binding sites BS1 and BS2 in terms of binding pockets motif, as well as the preferential affinities of eight anti-viral drugs to each of the two binding sites were described. Recent Cryogenic Electron Microscopy (Cryo-EM) studies on the RdRp revealed that two suramin molecules, a SARS-CoV-2 inhibitor, bind to RdRp in two different sites with distinctive interaction landscape. Here, we provide the first account of investigating the combined inhibitor binding to both binding sites, and whether the binding of two inhibitors molecules concurrently is "Cooperative binding" or not. It should be noted that the binding of inhibitors to different sites do not necessary constitute mutually independent events, therefore, we investigated two scenarios to better understand cooperativity: simultaneous binding and sequential binding. It has been demonstrated by binding free energy calculations (MM/PBSA) and piecewise linear potential (PLP) interaction energy analysis that the co-binding of two suramin molecules is not cooperative in nature; rather, when compared to individual binding, both molecules adversely affect one another's binding affinities. This observation appeared to be primarily due to RdRp's rigidity, which prevented both ligands from fitting comfortably within the catalytic chamber. Instead, the suramin molecules showed a tendency to change their orientation within the binding pockets in order to maintain their binding to the protein, but at the expense of the ligand internal energies. Although co-binding resulted in the loss of several important key interactions, a few interactions were conserved, and these appear to be crucial in preserving the binding of ligands in the active site. The structural and mechanistic details of this study will be useful for future research on creating and developing RdRp inhibitors against SARS-CoV-2.
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Affiliation(s)
- Kamel Metwally
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Tabuk, Tabuk, 71491, Saudi Arabia.
- Department of Medicinal Chemistry, Faculty of Pharmacy, Zagazig University, Zagazig, 44519, Egypt.
| | - Nader E Abo-Dya
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Tabuk, Tabuk, 71491, Saudi Arabia
- Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy, Zagazig University, Zagazig, 44519, Egypt
| | - Ahmed M E Hamdan
- Department of Pharmacy Practice, Faculty of Pharmacy, University of Tabuk, Tabuk, 71491, Saudi Arabia
| | - Maram N Alrashidi
- Pharm D Program, Faculty of Pharmacy, University of Tabuk, Tabuk, 71491, Saudi Arabia
| | - Mansour S Alturki
- Department of Pharmaceutical Chemistry, College of Clinical Pharmacy, Imam Abdulrahman Bin Faisal University, Dammam, 34212, Saudi Arabia
| | - Omar M Aly
- Medicinal Chemistry Department Faculty of Pharmacy Port Said University, Port Said, 42526, Egypt
| | - Aimen Aljoundi
- Molecular Bio-computation and Drug Design Laboratory, School of Health Sciences, University of KwaZulu-Natal, Westville Campus, Durban, 4001, South Africa
| | - Mahmoud Ibrahim
- CompChem Lab, Chemistry Department, Faculty of Science, Minia University, Minia, 61519, Egypt
| | - Mahmoud E S Soliman
- Molecular Bio-computation and Drug Design Laboratory, School of Health Sciences, University of KwaZulu-Natal, Westville Campus, Durban, 4001, South Africa.
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3
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Eisner D, Neher E, Taschenberger H, Smith G. Physiology of intracellular calcium buffering. Physiol Rev 2023; 103:2767-2845. [PMID: 37326298 DOI: 10.1152/physrev.00042.2022] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 05/08/2023] [Accepted: 06/11/2023] [Indexed: 06/17/2023] Open
Abstract
Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.
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Affiliation(s)
- David Eisner
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
| | - Erwin Neher
- Membrane Biophysics Laboratory, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Godfrey Smith
- School of Cardiovascular and Metabolic Health, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow, United Kingdom
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Mishra V, Adlakha N. Spatio temporal interdependent calcium and buffer dynamics regulating DAG in a hepatocyte cell due to obesity. J Bioenerg Biomembr 2023; 55:249-266. [PMID: 37460636 DOI: 10.1007/s10863-023-09973-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Accepted: 06/23/2023] [Indexed: 09/12/2023]
Abstract
Calcium ions (Ca2+) serve as a crucial signaling mechanism in almost all cells. The buffers are proteins that bind free Ca2+ to reduce the cell's Ca2+ concentration. The most studies reported in the past on calcium signaling in various cells have considered the buffer concentration as constant in the cell. However, buffers also diffuse and their concentration varies dynamically in the cells. Almost no work has been reported on interdependent calcium and buffer dynamics in the cells. In the present study, a model is proposed for inter-dependent spatio-temporal dynamics of calcium and buffer by coupling reaction-diffusion equations of Ca2+ and buffer in a hepatocyte cell. Boundary and initial conditions are framed based on the physiological state of the cell. The effect of various parameters viz. inositol 1,4,5-triphosphate receptor (IP3R), diffusion coefficient, SERCA pump and ryanodine receptor (RyR) on spatio-temporal dynamics of calcium and buffer regulating diacylglycerol (DAG) in a normal and obese hepatocyte cell has been studied using finite element simulation. From the results, it is concluded that the dynamics of calcium and buffer impact each other significantly along the spatio-temporal dimensions, thereby affecting the regulation of all the processes including DAG in a hepatocyte cell. The proposed model is more realistic than the existing ones, as the interdependent system dynamics of calcium and buffer have different regulatory impacts as compared to the individual and independent dynamics of these signaling processes in a hepatocyte cell.
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Affiliation(s)
- Vedika Mishra
- Department of Mathematics, SVNIT, Gujarat, 395007, Surat, India.
| | - Neeru Adlakha
- Department of Mathematics, SVNIT, Gujarat, 395007, Surat, India
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5
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Wender M, Bornschein G, Brachtendorf S, Hallermann S, Eilers J, Schmidt H. Ca v2.2 Channels Sustain Vesicle Recruitment at a Mature Glutamatergic Synapse. J Neurosci 2023; 43:4005-4018. [PMID: 37185239 PMCID: PMC10255130 DOI: 10.1523/jneurosci.1279-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 04/06/2023] [Accepted: 04/08/2023] [Indexed: 05/17/2023] Open
Abstract
The composition of voltage-gated Ca2+ channel (Cav) subtypes that gate action potential (AP)-evoked release changes during the development of mammalian CNS synapses. Cav2.2 and Cav2.3 lose their function in gating-evoked release during postnatal synapse maturation. In mature boutons, Cav2.1 currents provide the almost exclusive trigger for evoked release, and Cav2.3 currents are required for the induction of presynaptic long-term potentiation. However, the functional significance of Cav2.2 remained elusive in mature boutons, although they remain present at active zones and continue contributing significantly to presynaptic Ca2+ influx. Here, we addressed the functional significance of Cav2.2 and Cav2.3 at mature parallel-fiber (PF) to Purkinje neuron synapses of mice of either sex. These synapses are known to exhibit the corresponding developmental Cav subtype changes in gating release. We addressed two hypotheses, namely that Cav2.2 and Cav2.3 are involved in triggering spontaneous glutamate release and that they are engaged in vesicle recruitment during repetitive evoked release. We found that spontaneous miniature release is Ca2+ dependent. However, experiments with Cav subtype-specific blockers excluded the spontaneous opening of Cavs as the Ca2+ source for spontaneous glutamate release. Thus, neither Cav2.2 nor Cav2.3 controls spontaneous release from PF boutons. Furthermore, vesicle recruitment during brief bursts of APs was also independent of Ca2+ influx through Cav2.2 and Cav2.3. However, Cav2.2, but not Cav2.3, currents significantly boosted vesicle recruitment during sustained high-frequency synaptic transmission. Thus, in mature PF boutons Cav2.2 channels are specifically required to sustain synaptic transmission during prolonged neuronal activity.SIGNIFICANCE STATEMENT At young CNS synapses, action potential-evoked release is gated via three subtypes of voltage-gated Ca2+ channels: Cav2.1, Cav2.2, and Cav2.3. During postnatal maturation, Cav2.2 and Cav2.3 lose their function in gating evoked release, such that at mature synapses Cav2.1 provides the almost exclusive source for triggering evoked release. Cav2.3 currents are required for the induction of presynaptic long-term potentiation. However, the function of the still abundant Cav2.2 in mature boutons remained largely elusive. Here, we studied mature cerebellar parallel-fiber synapses and found that Cav2.2 does not control spontaneous release. However, Ca2+ influx through Cav2.2 significantly boosted vesicle recruitment during trains of action potentials. Thus, Cav2.2 in mature parallel-fiber boutons participate in sustaining synaptic transmission during prolonged activity.
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Affiliation(s)
- Magdalena Wender
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
| | - Grit Bornschein
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
| | - Simone Brachtendorf
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
| | - Stefan Hallermann
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
| | - Jens Eilers
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
| | - Hartmut Schmidt
- Carl Ludwig Institute for Physiology, Medical Faculty, Leipzig University, 04103 Leipzig, Germany
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Mitra S, Basu S, Singh O, Srivastava A, Singru PS. Calcium-binding proteins typify the dopaminergic neuronal subtypes in the ventral tegmental area of zebra finch, Taeniopygia guttata. J Comp Neurol 2022; 530:2562-2586. [PMID: 35715989 DOI: 10.1002/cne.25352] [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: 11/15/2021] [Revised: 05/09/2022] [Accepted: 05/11/2022] [Indexed: 11/11/2022]
Abstract
Calcium-binding proteins (CBPs) regulate neuronal function in midbrain dopamine (DA)-ergic neurons in mammals by buffering and sensing the intracellular Ca2+ , and vesicular release. In birds, the equivalent set of neurons are important in song learning, directed singing, courtship, and energy balance, yet the status of CBPs in these neurons is unknown. Herein, for the first time, we probe the nature of CBPs, namely, Calbindin-, Calretinin-, Parvalbumin-, and Secretagogin-expressing DA neurons in the ventral tegmental area (VTA) and substantia nigra (SN) in the midbrain of zebra finch, Taeniopygia guttata. qRT-PCR analysis of ventral midbrain tissue fragment revealed higher Calbindin- and Calretinin-mRNA levels compared to Parvalbumin and Secretagogin. Application of immunofluorescence showed CBP-immunoreactive (-i) neurons in VTA (anterior [VTAa], mid [VTAm], caudal [VTAc]), SN (compacta [SNc], and reticulata [SNr]). Compared to VTAa, higher Calbindin- and Parvalbumin-immunoreactivity (-ir), and lower Calretinin-ir were observed in VTAm and VTAc. Secretagogin-ir was highly localized to VTAa. In SN, Calbindin- and Calretinin-ir were higher in SNc, SNr was Parvalbumin enriched, and Secretagogin-ir was not detected. Weak, moderate, and intense tyrosine hydroxylase (TH)-i VTA neurons were demarcated as subtypes 1, 2, and 3, respectively. While subtype 1 TH-i neurons were neither Calbindin- nor Calretinin-i, ∼80 and ∼65% subtype 2 and ∼30 and ∼45% subtype 3 TH-i neurons co-expressed Calbindin and Calretinin, respectively. All TH-i neuronal subtypes co-expressed Parvalbumin with reciprocal relationship with TH-ir. We suggest that the CBPs may determine VTA DA neuronal heterogeneity and differentially regulate their activity in T. guttata.
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Affiliation(s)
- Saptarsi Mitra
- School of Biological Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Sumela Basu
- School of Biological Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Omprakash Singh
- School of Biological Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Abhinav Srivastava
- School of Biological Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
| | - Praful S Singru
- School of Biological Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, India.,Homi Bhabha National Institute (HBNI), Mumbai, India
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Zhang C, Wang M, Lin S, Xie R. Calretinin-Expressing Synapses Show Improved Synaptic Efficacy with Reduced Asynchronous Release during High-Rate Activity. J Neurosci 2022; 42:2729-2742. [PMID: 35165172 PMCID: PMC8973423 DOI: 10.1523/jneurosci.1773-21.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 01/27/2022] [Accepted: 02/07/2022] [Indexed: 11/21/2022] Open
Abstract
Calretinin (CR) is a major calcium binding protein widely expressed in the CNS. However, its synaptic function remains largely elusive. At the auditory synapse of the endbulb of Held, CR is selectively expressed in different subtypes. Combining electrophysiology with immunohistochemistry, we investigated the synaptic transmission at the endbulb of Held synapses with and without endogenous CR expression in mature CBA/CAJ mice of either sex. Two synapse subtypes showed similar basal synaptic transmission, except a larger quantal size in CR-expressing synapses. During high-rate stimulus trains, CR-expressing synapses showed improved synaptic efficacy with significantly less depression and lower asynchronous release, suggesting more efficient exocytosis than non-CR-expressing synapses. Conversely, CR-expressing synapses had a smaller readily releasable pool size, which was countered by higher release probability and faster synaptic recovery to support sustained release during high-rate activity. EGTA-AM treatment did not change the synaptic transmission of CR-expressing synapses, but reduced synaptic depression and decreased asynchronous release at non-CR-expressing synapses, suggesting that CR helps to minimize calcium accumulation during high-rate activity. Both synapses express parvalbumin, another calcium-binding protein with slower kinetics and higher affinity than CR, but not calbindin. Furthermore, CR-expressing synapses only express the fast isoform of vesicular glutamate transporter 1 (VGluT1), while most non-CR-expressing synapses express both VGluT1 and the slower VGluT2, which may underlie their lagged synaptic recovery. The findings suggest that, paired with associated synaptic machinery, differential CR expression regulates synaptic efficacy among different subtypes of auditory nerve synapses to accomplish distinctive physiological functions in transmitting auditory information at high rates.SIGNIFICANCE STATEMENT CR is a major calcium-binding protein in the brain. It remains unclear how endogenous CR impacts synaptic transmission. We investigated the question at the large endbulb of Held synapses with selective CR expression and found that CR-expressing and non-CR-expressing synapses had similar release properties under basal synaptic transmission. During high-rate activity, however, CR-expressing synapses showed improved synaptic efficacy with less depression, lower asynchronous release, and faster recovery. Furthermore, CR-expressing synapses use exclusive VGluT1 to refill synaptic vesicles, while non-CR-expressing synapses use both VGluT1 and the slower isoform of VGluT2. Our findings suggest that CR may play significant roles in promoting synaptic efficacy during high-rate activity, and selective CR expression can differentially impact signal processing among different synapses.
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Affiliation(s)
- Chuangeng Zhang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Meijian Wang
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Shengyin Lin
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
| | - Ruili Xie
- Department of Otolaryngology-Head and Neck Surgery, The Ohio State University, Columbus, Ohio 43210
- Department of Neuroscience, The Ohio State University, Columbus, Ohio 43210
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Differential distribution of inhibitory neuron types in subregions of claustrum and dorsal endopiriform nucleus of the short-tailed fruit bat. Brain Struct Funct 2022; 227:1615-1640. [PMID: 35188589 DOI: 10.1007/s00429-022-02459-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 01/17/2022] [Indexed: 12/22/2022]
Abstract
Few brain regions have such wide-ranging inputs and outputs as the claustrum does, and fewer have posed equivalent challenges in defining their structural boundaries. We studied the distributions of three calcium-binding proteins-calretinin, parvalbumin, and calbindin-in the claustrum and dorsal endopiriform nucleus of the fruit bat, Carollia perspicillata. The proportionately large sizes of claustrum and dorsal endopiriform nucleus in Carollia brain afford unique access to these structures' intrinsic anatomy. Latexin immunoreactivity permits a separation of claustrum into core and shell subregions and an equivalent separation of dorsal endopiriform nucleus. Using latexin labeling, we found that the claustral shell in Carollia brain can be further subdivided into at least four distinct subregions. Calretinin and parvalbumin immunoreactivity reinforced the boundaries of the claustral core and its shell subregions with diametrically opposite distribution patterns. Calretinin, parvalbumin, and calbindin all colocalized with GAD67, indicating that these proteins label inhibitory neurons in both claustrum and dorsal endopiriform nucleus. Calretinin, however, also colocalized with latexin in a subset of neurons. Confocal microscopy revealed appositions that suggest synaptic contacts between cells labeled for each of the three calcium-binding proteins and latexin-immunoreactive somata in claustrum and dorsal endopiriform nucleus. Our results indicate significant subregional differences in the intrinsic inhibitory connectivity within and between claustrum and dorsal endopiriform nucleus. We conclude that the claustrum is structurally more complex than previously appreciated and that claustral and dorsal endopiriform nucleus subregions are differentially modulated by multiple inhibitory systems. These findings can also account for the excitability differences between claustrum and dorsal endopiriform nucleus described previously.
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Eshra A, Schmidt H, Eilers J, Hallermann S. Calcium dependence of neurotransmitter release at a high fidelity synapse. eLife 2021; 10:70408. [PMID: 34612812 PMCID: PMC8494478 DOI: 10.7554/elife.70408] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 08/24/2021] [Indexed: 11/15/2022] Open
Abstract
The Ca2+-dependence of the priming, fusion, and replenishment of synaptic vesicles are fundamental parameters controlling neurotransmitter release and synaptic plasticity. Despite intense efforts, these important steps in the synaptic vesicles’ cycle remain poorly understood due to the technical challenge in disentangling vesicle priming, fusion, and replenishment. Here, we investigated the Ca2+-sensitivity of these steps at mossy fiber synapses in the rodent cerebellum, which are characterized by fast vesicle replenishment mediating high-frequency signaling. We found that the basal free Ca2+ concentration (<200 nM) critically controls action potential-evoked release, indicating a high-affinity Ca2+ sensor for vesicle priming. Ca2+ uncaging experiments revealed a surprisingly shallow and non-saturating relationship between release rate and intracellular Ca2+ concentration up to 50 μM. The rate of vesicle replenishment during sustained elevated intracellular Ca2+ concentration exhibited little Ca2+-dependence. Finally, quantitative mechanistic release schemes with five Ca2+ binding steps incorporating rapid vesicle replenishment via parallel or sequential vesicle pools could explain our data. We thus show that co-existing high- and low-affinity Ca2+ sensors mediate priming, fusion, and replenishment of synaptic vesicles at a high-fidelity synapse.
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Affiliation(s)
- Abdelmoneim Eshra
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Stefan Hallermann
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
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10
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Chen Y, Matveev V. Stationary Ca 2+ nanodomains in the presence of buffers with two binding sites. Biophys J 2021; 120:1942-1956. [PMID: 33771472 DOI: 10.1016/j.bpj.2021.03.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 03/06/2021] [Accepted: 03/11/2021] [Indexed: 10/21/2022] Open
Abstract
We examine closed-form approximations for the equilibrium Ca2+ and buffer concentrations near a point Ca2+ source representing a Ca2+ channel, in the presence of a mobile buffer with two Ca2+ binding sites activated sequentially and possessing distinct binding affinities and kinetics. This allows us to model the impact on Ca2+ nanodomains of realistic endogenous Ca2+ buffers characterized by cooperative Ca2+ binding, such as calretinin. The approximations we present involve a combination or rational and exponential functions, whose parameters are constrained using the series interpolation method that we recently introduced for the case of simpler Ca2+ buffers with a single Ca2+ binding site. We conduct extensive parameter sensitivity analysis and show that the obtained closed-form approximations achieve reasonable qualitative accuracy for a wide range of buffer's Ca2+ binding properties and other relevant model parameters. In particular, the accuracy of the derived approximants exceeds that of the rapid buffering approximation in large portions of the relevant parameter space.
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Affiliation(s)
- Yinbo Chen
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey
| | - Victor Matveev
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey.
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11
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Chen Y, Muratov CB, Matveev V. Efficient Approximations for Stationary Single-Channel Ca 2+ Nanodomains across Length Scales. Biophys J 2020; 119:1239-1254. [PMID: 32877663 DOI: 10.1016/j.bpj.2020.06.038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 06/06/2020] [Accepted: 06/10/2020] [Indexed: 10/23/2022] Open
Abstract
We consider the stationary solution for the Ca2+ concentration near a point Ca2+ source describing a single-channel Ca2+ nanodomain in the presence of a single mobile Ca2+ buffer with 1:1 Ca2+ binding. We present computationally efficient approximants that estimate stationary single-channel Ca2+ nanodomains with great accuracy in broad regions of parameter space. The presented approximants have a functional form that combines rational and exponential functions, which is similar to that of the well-known excess buffer approximation and the linear approximation but with parameters estimated using two novel, to our knowledge, methods. One of the methods involves interpolation between the short-range Taylor series of the free buffer concentration and its long-range asymptotic series in inverse powers of distance from the channel. Although this method has already been used to find Padé (rational-function) approximants to single-channel Ca2+ and buffer concentrations, extending this method to interpolants combining exponential and rational functions improves accuracy in a significant fraction of the relevant parameter space. A second method is based on the variational approach and involves a global minimization of an appropriate functional with respect to parameters of the chosen approximations. An extensive parameter-sensitivity analysis is presented, comparing these two methods with previously developed approximants. Apart from increased accuracy, the strength of these approximants is that they can be extended to more realistic buffers with multiple binding sites characterized by cooperative Ca2+ binding, such as calmodulin and calretinin.
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Affiliation(s)
- Yinbo Chen
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey
| | - Cyrill B Muratov
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey
| | - Victor Matveev
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey.
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12
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Schwaller B. Cytosolic Ca 2+ Buffers Are Inherently Ca 2+ Signal Modulators. Cold Spring Harb Perspect Biol 2020; 12:cshperspect.a035543. [PMID: 31308146 DOI: 10.1101/cshperspect.a035543] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
For precisely regulating intracellular Ca2+ signals in a time- and space-dependent manner, cells make use of various components of the "Ca2+ signaling toolkit," including Ca2+ entry and Ca2+ extrusion systems. A class of cytosolic Ca2+-binding proteins termed Ca2+ buffers serves as modulators of such, mostly short-lived Ca2+ signals. Prototypical Ca2+ buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Although initially considered to function as pure Ca2+ buffers, that is, as intracellular Ca2+ signal modulators controlling the shape (amplitude, decay, spread) of Ca2+ signals, evidence has accumulated that calbindin-D28k and calretinin have additional Ca2+ sensor functions. These other functions are brought about by direct interactions with target proteins, thereby modulating their targets' function/activity. Dysregulation of Ca2+ buffer expression is associated with several neurologic/neurodevelopmental disorders including autism spectrum disorder (ASD) and schizophrenia. In some cases, the presence of these proteins is presumed to confer a neuroprotective effect, as evidenced in animal models of Parkinson's or Alzheimer's disease.
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Affiliation(s)
- Beat Schwaller
- Department of Anatomy, Section of Medicine, University of Fribourg, CH-1700 Fribourg, Switzerland
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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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Kusch V, Bornschein G, Loreth D, Bank J, Jordan J, Baur D, Watanabe M, Kulik A, Heckmann M, Eilers J, Schmidt H. Munc13-3 Is Required for the Developmental Localization of Ca 2+ Channels to Active Zones and the Nanopositioning of Ca v2.1 Near Release Sensors. Cell Rep 2019; 22:1965-1973. [PMID: 29466725 DOI: 10.1016/j.celrep.2018.02.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Revised: 12/01/2017] [Accepted: 01/31/2018] [Indexed: 12/20/2022] Open
Abstract
Spatial relationships between Cav channels and release sensors at active zones (AZs) are a major determinant of synaptic fidelity. They are regulated developmentally, but the underlying molecular mechanisms are largely unclear. Here, we show that Munc13-3 regulates the density of Cav2.1 and Cav2.2 channels, alters the localization of Cav2.1, and is required for the development of tight, nanodomain coupling at parallel-fiber AZs. We combined EGTA application and Ca2+-channel pharmacology in electrophysiological and two-photon Ca2+ imaging experiments with quantitative freeze-fracture immunoelectron microscopy and mathematical modeling. We found that a normally occurring developmental shift from release being dominated by Ca2+ influx through Cav2.1 and Cav2.2 channels with domain overlap and loose coupling (microdomains) to a nanodomain Cav2.1 to sensor coupling is impaired in Munc13-3-deficient synapses. Thus, at AZs lacking Munc13-3, release remained triggered by Cav2.1 and Cav2.2 microdomains, suggesting a critical role of Munc13-3 in the formation of release sites with calcium channel nanodomains.
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Affiliation(s)
- Valentin Kusch
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
| | - Grit Bornschein
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
| | - Desiree Loreth
- Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Julia Bank
- Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Johannes Jordan
- Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - David Baur
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
| | - Masahiko Watanabe
- Department of Anatomy, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
| | - Akos Kulik
- Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
| | - Manfred Heckmann
- Department of Physiology, Neurophysiology, Medical Faculty, University of Würzburg, Röntgenring 9, 97070 Würzburg, Germany
| | - Jens Eilers
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany.
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15
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Bolshakov AP, Kolleker A, Volkova EP, Valiullina-Rakhmatullina F, Kolosov PM, Rozov A. Overexpression of Calretinin Enhances Short-Term Synaptic Depression. Front Cell Neurosci 2019; 13:91. [PMID: 30930749 PMCID: PMC6425694 DOI: 10.3389/fncel.2019.00091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2018] [Accepted: 02/22/2019] [Indexed: 12/03/2022] Open
Abstract
Analysis of the effects of various proteins on short-term synaptic plasticity is a difficult task, which may require the use of knockout animals. Here, we propose an alternative experimental approach for studying the roles of desired proteins in synaptic plasticity. We packed the Ca2+-binding protein calretinin and the fluorescent protein Venus into AAV and injected the concentrated viral suspension into the neocortex of newborn rats. The infected layer 2/3 pyramidal cells were identified in rat cortical slices using Venus fluorescence. Analysis of short-term synaptic plasticity using paired patch clamp recordings between layer 2/3 pyramidal cells (presynaptic cell) and fast-spiking (FS) interneurons (post-synaptic cell) showed that calretinin expression in the pyramidal cells did not change the failure rate in this synapse but did decrease synaptic delay. Analysis of the parameters of short-term synaptic plasticity showed that the amplitude of the first EPSP in the train was not affected by calretinin, however, calretinin strongly enhanced short-term depression. In addition, we found that the effect of calretinin depended on the presynaptic firing frequency: an increase in frequency resulted in enhancement of synaptic depression.
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Affiliation(s)
- Alexey P Bolshakov
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences (RAS), Moscow, Russia.,Research Laboratory of Electrophysiology, Pirogov Russian National Research Medical University, Moscow, Russia
| | - Alexander Kolleker
- Max Planck Institute for Medical Research, Department of Molecular Neurobiology, Heidelberg, Germany.,Buryat State University, Medical Institute, Ulan-Ude, Russia
| | - Evgenia P Volkova
- Research Laboratory of Electrophysiology, Pirogov Russian National Research Medical University, Moscow, Russia
| | | | - Peter M Kolosov
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences (RAS), Moscow, Russia
| | - Andrei Rozov
- Laboratory of Neurobiology, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russia.,Department of Physiology and Pathophysiology, University of Heidelberg, Heidelberg, Germany
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16
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Abstract
Fundamental cell processes such as synaptic neurotransmitter release, endocrine hormone secretion, and myocyte contraction are controlled by highly localized calcium (Ca2+) signals resulting from brief openings of trans-membrane Ca2+ channels. On short temporal and spatial scales, the corresponding local Ca2+ nanodomains formed in the vicinity of a single or several open Ca2+ channels can be effectively approximated by quasi-stationary solutions. The rapid buffering approximation (RBA) is one of the most powerful of such approximations, and is based on the assumption of instantaneous equilibration of the bimolecular Ca2+ buffering reaction, combined with the conservation condition for the total Ca2+ and buffer molecule numbers. Previously, RBA has been generalized to an arbitrary arrangement of Ca2+ channels on a flat membrane, in the presence of any number of simple Ca2+ buffers with one-to-one Ca2+ binding stoichiometry. However, many biological buffers have multiple binding sites. For example, buffers and sensors phylogenetically related to calmodulin consist of two Ca2+-binding domains (lobes), with each domain binding two Ca2+ ions in a cooperative manner. Here we consider an extension of RBA to such buffers with two interdependent Ca2+ binding sites. We show that in the presence of such buffers, RBA solution is given by the solution to a cubic equation, analogous to the quadratic equation describing RBA in the case of a simple, one-to-one Ca2+ buffer. We examine in detail the dependence of RBA accuracy on buffering parameters, to reveal conditions under which RBA provides sufficient precision.
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Affiliation(s)
- Victor Matveev
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey.
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17
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Bornschein G, Schmidt H. Synaptotagmin Ca 2+ Sensors and Their Spatial Coupling to Presynaptic Ca v Channels in Central Cortical Synapses. Front Mol Neurosci 2019; 11:494. [PMID: 30697148 PMCID: PMC6341215 DOI: 10.3389/fnmol.2018.00494] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 12/21/2018] [Indexed: 11/21/2022] Open
Abstract
Ca2+ concentrations drop rapidly over a distance of a few tens of nanometers from an open voltage-gated Ca2+ channel (Cav), thereby, generating a spatially steep and temporally short-lived Ca2+ gradient that triggers exocytosis of a neurotransmitter filled synaptic vesicle. These non-steady state conditions make the Ca2+-binding kinetics of the Ca2+ sensors for release and their spatial coupling to the Cavs important parameters of synaptic efficacy. In the mammalian central nervous system, the main release sensors linking action potential mediated Ca2+ influx to synchronous release are Synaptotagmin (Syt) 1 and 2. We review here quantitative work focusing on the Ca2+ kinetics of Syt2-mediated release. At present similar quantitative detail is lacking for Syt1-mediated release. In addition to triggering release, Ca2+ remaining bound to Syt after the first of two successive high-frequency activations was found to be capable of facilitating release during the second activation. More recently, the Ca2+ sensor Syt7 was identified as additional facilitation sensor. We further review how several recent functional studies provided quantitative insights into the spatial topographical relationships between Syts and Cavs and identified mechanisms regulating the sensor-to-channel coupling distances at presynaptic active zones. Most synapses analyzed in matured cortical structures were found to operate at tight, nanodomain coupling. For fast signaling synapses a developmental switch from loose, microdomain to tight, nanodomain coupling was found. The protein Septin5 has been known for some time as a developmentally down-regulated “inhibitor” of tight coupling, while Munc13-3 was found only recently to function as a developmentally up-regulated mediator of tight coupling. On the other hand, a highly plastic synapse was found to operate at loose coupling in the matured hippocampus. Together these findings suggest that the coupling topography and its regulation is a specificity of the type of synapse. However, to definitely draw such conclusion our knowledge of functional active zone topographies of different types of synapses in different areas of the mammalian brain is too incomplete.
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Affiliation(s)
- Grit Bornschein
- Carl-Ludwig Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Hartmut Schmidt
- Carl-Ludwig Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany
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18
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Lichvarova L, Henzi T, Safiulina D, Kaasik A, Schwaller B. Parvalbumin alters mitochondrial dynamics and affects cell morphology. Cell Mol Life Sci 2018; 75:4643-4666. [PMID: 30255402 PMCID: PMC6208788 DOI: 10.1007/s00018-018-2921-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 08/24/2018] [Accepted: 09/18/2018] [Indexed: 12/26/2022]
Abstract
The Ca2+-binding protein parvalbumin (PV) and mitochondria play important roles in Ca2+ signaling, buffering and sequestration. Antagonistic regulation of PV and mitochondrial volume is observed in in vitro and in vivo model systems. Changes in mitochondrial morphology, mitochondrial volume and dynamics (fusion, fission, mitophagy) resulting from modulation of PV were investigated in MDCK epithelial cells with stable overexpression/downregulation of PV. Increased PV levels resulted in smaller, roundish cells and shorter mitochondria, the latter phenomenon related to reduced fusion rates and decreased expression of genes involved in mitochondrial fusion. PV-overexpressing cells displayed increased mitophagy, a likely cause for the decreased mitochondrial volumes and the smaller overall cell size. Cells showed lower mobility in vitro, paralleled by reduced protrusions. Constitutive PV down-regulation in PV-overexpressing cells reverted mitochondrial morphology and fractional volume to the state present in control MDCK cells, resulting from increased mitochondrial movement and augmented fusion rates. PV-modulated, bi-directional and reversible mitochondrial dynamics are key to regulation of mitochondrial volume.
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Affiliation(s)
- Lucia Lichvarova
- Unit of Anatomy, Section of Medicine, University of Fribourg, Route Albert-Gockel 1, 1700, Fribourg, Switzerland
| | - Thomas Henzi
- Unit of Anatomy, Section of Medicine, University of Fribourg, Route Albert-Gockel 1, 1700, Fribourg, Switzerland
| | - Dzhamilja Safiulina
- Department of Pharmacology, Institute of Biomedicine and Translational Medicine, University of Tartu, 50411, Tartu, Estonia
| | - Allen Kaasik
- Department of Pharmacology, Institute of Biomedicine and Translational Medicine, University of Tartu, 50411, Tartu, Estonia
| | - Beat Schwaller
- Unit of Anatomy, Section of Medicine, University of Fribourg, Route Albert-Gockel 1, 1700, Fribourg, Switzerland.
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19
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Two-component latency distributions indicate two-step vesicular release at simple glutamatergic synapses. Nat Commun 2018; 9:3943. [PMID: 30258069 PMCID: PMC6158186 DOI: 10.1038/s41467-018-06336-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Accepted: 07/31/2018] [Indexed: 01/03/2023] Open
Abstract
It is often assumed that only stably docked synaptic vesicles can fuse following presynaptic action potential stimulation. However, during action potential trains docking sites are increasingly depleted, raising the question of the source of synaptic vesicles during sustained release. We have recently developed methods to reliably measure release latencies during high frequency trains at single synapses between parallel fibers and molecular layer interneurons. The latency distribution exhibits a single fast component at train onset but contains both a fast and a slow component later in the train. The contribution of the slow component increases with stimulation frequency and with release probability and decreases when blocking the docking step with latrunculin. These results suggest that the slow component reflects sequential docking and release in immediate succession. The transition from fast to slow component, as well as a later transition to asynchronous release, appear as successive adaptations of the synapse to maintain fidelity at the expense of time accuracy.
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Filadi R, Basso E, Lefkimmiatis K, Pozzan T. Beyond Intracellular Signaling: The Ins and Outs of Second Messengers Microdomains. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 981:279-322. [PMID: 29594866 DOI: 10.1007/978-3-319-55858-5_12] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A typical characteristic of eukaryotic cells compared to prokaryotes is represented by the spatial heterogeneity of the different structural and functional components: for example, most of the genetic material is surrounded by a highly specific membrane structure (the nuclear membrane), continuous with, yet largely different from, the endoplasmic reticulum (ER); oxidative phosphorylation is carried out by organelles enclosed by a double membrane, the mitochondria; in addition, distinct domains, enriched in specific proteins, are present in the plasma membrane (PM) of most cells. Less obvious, but now generally accepted, is the notion that even the concentration of small molecules such as second messengers (Ca2+ and cAMP in particular) can be highly heterogeneous within cells. In the case of most organelles, the differences in the luminal levels of second messengers depend either on the existence on their membrane of proteins that allow the accumulation/release of the second messenger (e.g., in the case of Ca2+, pumps, exchangers or channels), or on the synthesis and degradation of the specific molecule within the lumen (the autonomous intramitochondrial cAMP system). It needs stressing that the existence of a surrounding membrane does not necessarily imply the existence of a gradient between the cytosol and the organelle lumen. For example, the nuclear membrane is highly permeable to both Ca2+ and cAMP (nuclear pores are permeable to solutes up to 50 kDa) and differences in [Ca2+] or [cAMP] between cytoplasm and nucleoplasm are not seen in steady state and only very transiently during cell activation. A similar situation has been observed, as far as Ca2+ is concerned, in peroxisomes.
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Affiliation(s)
- Riccardo Filadi
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Emy Basso
- Institute of Neuroscience, Padova Section, National Research Council, Padova, Italy
| | - Konstantinos Lefkimmiatis
- Institute of Neuroscience, Padova Section, National Research Council, Padova, Italy
- Venetian Institute of Molecular Medicine, Padova, Italy
| | - Tullio Pozzan
- Department of Biomedical Sciences, University of Padova, Padova, Italy.
- Institute of Neuroscience, Padova Section, National Research Council, Padova, Italy.
- Venetian Institute of Molecular Medicine, Padova, Italy.
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21
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Tran V, Stricker C. Diffusion of Ca 2+ from Small Boutons en Passant into the Axon Shapes AP-Evoked Ca 2+ Transients. Biophys J 2018; 115:1344-1356. [PMID: 30103908 DOI: 10.1016/j.bpj.2018.07.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 07/01/2018] [Accepted: 07/16/2018] [Indexed: 01/16/2023] Open
Abstract
Not only the amplitude but also the time course of a presynaptic Ca2+ transient determine multiple aspects of synaptic transmission. In small bouton-type synapses, the mechanisms underlying the Ca2+ decay kinetics have not been fully investigated. Here, factors that shape an action-potential-evoked Ca2+ transient were quantitatively studied in synaptic boutons of neocortical layer 5 pyramidal neurons. Ca2+ transients were measured with different concentrations of fluorescent Ca2+ indicators and analyzed based on a single-compartment model. We found a small endogenous Ca2+-binding ratio (7 ± 2) and a high activity of Ca2+ transporters (0.64 ± 0.03 ms-1), both of which enable rapid clearance of Ca2+ from the boutons. However, contrary to predictions of the single-compartment model, the decay time course of the measured Ca2+ transients was biexponential and became prolonged during repetitive stimulation. Measurements of [Ca2+]i along the adjoining axon, together with an experimentally constrained model, showed that the initial fast decay of the Ca2+ transients predominantly arose from the diffusion of Ca2+ from the boutons into the axon. Therefore, for small boutons en passant, factors like terminal volume, axon diameter, and the concentration of mobile Ca2+-binding molecules are critical determinants of Ca2+ dynamics and thus Ca2+-dependent processes, including short-term synaptic plasticity.
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Affiliation(s)
- Van Tran
- Eccles Institute of Neuroscience, JCSMR.
| | - Christian Stricker
- Eccles Institute of Neuroscience, JCSMR; ANU Medical School, ANU, Acton, Australian Capital Territory, Australia
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22
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Kawaguchi SY, Sakaba T. Fast Ca 2+ Buffer-Dependent Reliable but Plastic Transmission at Small CNS Synapses Revealed by Direct Bouton Recording. Cell Rep 2018; 21:3338-3345. [PMID: 29262314 DOI: 10.1016/j.celrep.2017.11.072] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/17/2017] [Accepted: 11/18/2017] [Indexed: 01/07/2023] Open
Abstract
The small size of presynaptic structures and their rapid function have obscured the mechanisms underlying neurotransmission and plasticity. To dissect the function of conventional small presynaptic boutons, we performed direct recording using axon varicosities of cerebellar granule cells (GCs), a parallel-fiber bouton, in dissociated culture, in which pre- and postsynaptic paired recordings are feasible. Identification and accessibility of EGFP-labeled GC boutons allowed us to patch-clamp record presynaptic voltage-gated Ca2+ currents and membrane capacitances, together with excitatory postsynaptic currents. We find that GC boutons have 20 readily releasable vesicles, which are loosely coupled to Ca2+ channels and rapidly replenished, and that synaptic strength and short-term plasticity are tightly regulated by intracellular Ca2+ buffering. Our functional dissection of small boutons thus reveals the sophisticated design of small synapses capable of reliable but plastic outputs with limited resources.
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Affiliation(s)
- Shin-Ya Kawaguchi
- Graduate School of Brain Science, Doshisha University, Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan; Society-Academia Collaboration for Innovation, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan; Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan.
| | - Takeshi Sakaba
- Graduate School of Brain Science, Doshisha University, Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
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Blum W, Pecze L, Rodriguez JW, Steinauer M, Schwaller B. Regulation of calretinin in malignant mesothelioma is mediated by septin 7 binding to the CALB2 promoter. BMC Cancer 2018; 18:475. [PMID: 29699512 PMCID: PMC5922012 DOI: 10.1186/s12885-018-4385-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 04/17/2018] [Indexed: 12/18/2022] Open
Abstract
Background The calcium-binding protein calretinin (gene name: CALB2) is currently considered as the most sensitive and specific marker for the diagnosis of malignant mesothelioma (MM). MM is a very aggressive tumor strongly linked to asbestos exposure and with no existing cure so far. The mechanisms of calretinin regulation, as well as its distinct function in MM are still poorly understood. Methods We searched for transcription factors binding to the CALB2 promoter and modulating calretinin expression. For this, DNA-binding assays followed by peptide shotgun-mass spectroscopy analyses were used. CALB2 promoter activity was assessed by dual-luciferase reporter assays. Furthermore, we analyzed the effects of CALB2 promoter-binding proteins by lentiviral-mediated overexpression or down-regulation of identified proteins in MM cells. The modulation of expression of such proteins by butyrate was determined by subsequent Western blot analysis. Immunohistochemical analysis of embryonic mouse lung tissue served to verify the simultaneous co-expression of calretinin and proteins interacting with the CALB2 promoter during early development. Finally, direct interactions of calretinin with target proteins were evidenced by co-immunoprecipitation experiments. Results Septin 7 was identified as a butyrate-dependent transcription factor binding to a CALB2 promoter region containing butyrate-responsive elements (BRE) resulting in decreased calretinin expression. Accordingly, septin 7 overexpression decreased calretinin expression levels in MM cells. The regulation was found to operate bi-directionally, i.e. calretinin overexpression also decreased septin 7 levels. During murine embryonic development calretinin and septin 7 were found to be co-expressed in embryonic mesenchyme and undifferentiated mesothelial cells. In MM cells, calretinin and septin 7 colocalized during cytokinesis in distinct regions of the cleavage furrow and in the midbody region of mitotic cells. Co-immunoprecipitation experiments revealed this co-localization to be the result of a direct interaction between calretinin and septin 7. Conclusions Our results demonstrate septin 7 not only serving as a “cytoskeletal” protein, but also as a transcription factor repressing calretinin expression. The negative regulation of calretinin by septin 7 and vice versa sheds new light on mechanisms possibly implicated in MM formation and identifies these proteins as transcriptional regulators and putative targets for MM therapy. Electronic supplementary material The online version of this article (10.1186/s12885-018-4385-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Walter Blum
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700, Fribourg, Switzerland
| | - László Pecze
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700, Fribourg, Switzerland
| | | | - Martine Steinauer
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700, Fribourg, Switzerland
| | - Beat Schwaller
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700, Fribourg, Switzerland.
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Variations in Ca 2+ Influx Can Alter Chelator-Based Estimates of Ca 2+ Channel-Synaptic Vesicle Coupling Distance. J Neurosci 2018; 38:3971-3987. [PMID: 29563180 DOI: 10.1523/jneurosci.2061-17.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Revised: 02/23/2018] [Accepted: 02/28/2018] [Indexed: 12/20/2022] Open
Abstract
The timing and probability of synaptic vesicle fusion from presynaptic terminals is governed by the distance between voltage-gated Ca2+ channels (VGCCs) and Ca2+ sensors for exocytosis. This VGCC-sensor coupling distance can be determined from the fractional block of vesicular release by exogenous Ca2+ chelators, which depends on biophysical factors that have not been thoroughly explored. Using numerical simulations of Ca2+ reaction and diffusion, as well as vesicular release, we examined the contributions of conductance, density, and open duration of VGCCs, and the influence of endogenous Ca2+ buffers on the inhibition of exocytosis by EGTA. We found that estimates of coupling distance are critically influenced by the duration and amplitude of Ca2+ influx at active zones, but relatively insensitive to variations of mobile endogenous buffer. High concentrations of EGTA strongly inhibit vesicular release in close proximity (20-30 nm) to VGCCs if the flux duration is brief, but have little influence for longer flux durations that saturate the Ca2+ sensor. Therefore, the diversity in presynaptic action potential duration is sufficient to alter EGTA inhibition, resulting in errors potentially as large as 300% if Ca2+ entry durations are not considered when estimating VGCC-sensor coupling distances.SIGNIFICANT STATEMENT The coupling distance between voltage-gated Ca2+ channels and Ca2+ sensors for exocytosis critically determines the timing and probability of neurotransmitter release. Perfusion of presynaptic terminals with the exogenous Ca2+ chelator EGTA has been widely used for both qualitative and quantitative estimates of this distance. However, other presynaptic terminal parameters such as the amplitude and duration of Ca2+ entry can also influence EGTA inhibition of exocytosis, thus confounding conclusions based on EGTA alone. Here, we performed reaction-diffusion simulations of Ca2+-driven synaptic vesicle fusion, which delineate the critical parameters influencing an accurate prediction of coupling distance. Our study provides guidelines for characterizing and understanding how variability in coupling distance across chemical synapses could be estimated accurately.
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Hermanowicz-Sobieraj B, Bogus-Nowakowska K, Robak A. Calcium-binding proteins expression in the septum and cingulate cortex of the adult guinea pig. Ann Anat 2018; 215:30-39. [DOI: 10.1016/j.aanat.2017.09.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2017] [Revised: 09/11/2017] [Accepted: 09/13/2017] [Indexed: 01/08/2023]
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Pinto BI, Pupo A, García IE, Mena-Ulecia K, Martínez AD, Latorre R, Gonzalez C. Calcium binding and voltage gating in Cx46 hemichannels. Sci Rep 2017; 7:15851. [PMID: 29158540 PMCID: PMC5696461 DOI: 10.1038/s41598-017-15975-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 10/24/2017] [Indexed: 12/26/2022] Open
Abstract
The opening of connexin (Cx) hemichannels in the membrane is tightly regulated by calcium (Ca2+) and membrane voltage. Electrophysiological and atomic force microscopy experiments indicate that Ca2+ stabilizes the hemichannel closed state. However, structural data show that Ca2+ binding induces an electrostatic seal preventing ion transport without significant structural rearrangements. In agreement with the closed-state stabilization hypothesis, we found that the apparent Ca2+ sensitivity is increased as the voltage is made more negative. Moreover, the voltage and Ca2+ dependence of the channel kinetics indicate that the voltage sensor movement and Ca2+ binding are allosterically coupled. An allosteric kinetic model in which the Ca2+ decreases the energy necessary to deactivate the voltage sensor reproduces the effects of Ca2+ and voltage in Cx46 hemichannels. In agreement with the model and suggesting a conformational change that narrows the pore, Ca2+ inhibits the water flux through Cx hemichannels. We conclude that Ca2+ and voltage act allosterically to stabilize the closed conformation of Cx46 hemichannels.
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Affiliation(s)
- Bernardo I Pinto
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Amaury Pupo
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Isaac E García
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
- Facultad de Odontología, Universidad de Valparaíso, Valparaíso, Chile
| | - Karel Mena-Ulecia
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Agustín D Martínez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
| | - Carlos Gonzalez
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaíso, Valparaíso, Chile.
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The ontogenetic development of neurons containing calcium-binding proteins in the septum of the guinea pig: Late onset of parvalbumin immunoreactivity versus calbindin and calretinin. J Chem Neuroanat 2017; 79:22-31. [DOI: 10.1016/j.jchemneu.2016.10.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/07/2016] [Accepted: 10/18/2016] [Indexed: 10/20/2022]
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Fogli Iseppe A, Pignatelli A, Belluzzi O. Calretinin-Periglomerular Interneurons in Mice Olfactory Bulb: Cells of Few Words. Front Cell Neurosci 2016; 10:231. [PMID: 27774053 PMCID: PMC5054022 DOI: 10.3389/fncel.2016.00231] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 09/23/2016] [Indexed: 01/11/2023] Open
Abstract
Within the olfactory bulb (OB), periglomerular (PG) cells consist of various types of interneurons, generally classified by their chemical properties such as neurotransmitter and calcium binding proteins. Calretinin (CR) characterizes morphologically and functionally the more numerous and one of the less known subpopulation of PG cells in the OB. Using of transgenic mice expressing eGFP under the CR promoter, we have tried to obtain the first functional characterization of these cells. Electrophysiological recordings were made in these cells using the patch-clamp technique in thin slices. Using ion substitution methods and specific blockers, we dissected the main voltage-dependent conductances present, obtaining a complete kinetic description for each of them. The more peculiar property of these cells from the electrophysiological point of view is the presence only of a single K-current, A-type – there is no trace of delayed rectifier or of Ca-dependent K-current. Other currents identified, isolated and fully characterized are a fast sodium current, a small L-type calcium current, and an inward rectifier, h-type cationic current. As a consequence of the peculiar complement of voltage-dependent conductances present in these cells, and in particular the absence of delayed-rectifier potassium currents, under the functional point of view these cells present two interesting properties. First, in response to prolonged depolarisations, after the inactivation of the A-current these cells behave as a purely ohmic elements, showing no outward rectification. Second, the CR cells studied can respond only with a single action potential to excitatory inputs; since they send inhibitory synapses to projection neurones, they seem to be designed to inhibit responses of the main neurones to isolated, random excitatory signals, rapidly losing their vetoing effect in response to more structured, repetitive excitatory signals. We propose that a possible role for these rather untalkative interneurons in the intense exchange of messages within the OB might be that of improving the signal-to-noise ratio in the first stages of the olfactory information processing.
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Affiliation(s)
- Alex Fogli Iseppe
- Biology and Evolution - Neurobiology, Department of Life Sciences and Biotechnology, University of FerraraFerrara, Italy; Department of Neurobiology, Physiology and Behavior, University of California at Davis, DavisCA, USA
| | - Angela Pignatelli
- Biology and Evolution - Neurobiology, Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy
| | - Ottorino Belluzzi
- Biology and Evolution - Neurobiology, Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy
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Żakowski W. Neurochemistry of the Anterior Thalamic Nuclei. Mol Neurobiol 2016; 54:5248-5263. [DOI: 10.1007/s12035-016-0077-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Accepted: 08/23/2016] [Indexed: 01/19/2023]
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Ait Ouares K, Jaafari N, Canepari M. A generalised method to estimate the kinetics of fast Ca(2+) currents from Ca(2+) imaging experiments. J Neurosci Methods 2016; 268:66-77. [PMID: 27163479 DOI: 10.1016/j.jneumeth.2016.05.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 05/04/2016] [Accepted: 05/05/2016] [Indexed: 10/21/2022]
Abstract
BACKGROUND Fast Ca(2+) imaging using low-affinity fluorescent indicators allows tracking Ca(2+) neuronal influx at high temporal resolution. In some systems, where the Ca(2+)-bound indicator is linear with Ca(2+) entering the cell, the Ca(2+) current has same kinetics of the fluorescence time derivative. In other systems, like cerebellar Purkinje neuron dendrites, the time derivative strategy fails since fluorescence kinetics is affected by Ca(2+) binding proteins sequestering Ca(2+) from the indicator. NEW METHOD Our novel method estimates the kinetics of the Ca(2+) current in cells where the time course of fluorescence is not linear with Ca(2+) influx. The method is based on a two-buffer and two-indicator model, with three free parameters, where Ca(2+) sequestration from the indicator is mimicked by Ca(2+)-binding to the slower buffer. We developed a semi-automatic protocol to optimise the free parameters and the kinetics of the input current to match the experimental fluorescence change with the simulated curve of the Ca(2+)-bound indicator. RESULTS We show that the optimised input current is a good estimate of the real Ca(2+) current by validating the method both using computer simulations and data from real neurons. We report the first estimates of Ca(2+) currents associated with climbing fibre excitatory postsynaptic potentials in Purkinje neurons. COMPARISON WITH EXISTING METHODS The present method extends the possibility of studying Ca(2+) currents in systems where the existing time derivative approach fails. CONCLUSIONS The information available from our technique allows investigating the physiological behaviour of Ca(2+) channels under all possible conditions.
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Affiliation(s)
- Karima Ait Ouares
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Nadia Jaafari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- Laboratory for Interdisciplinary Physics, UMR 5588, Université Grenoble Alpes and CNRS, 38402 Saint Martin d'Hères, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, France; Institut National de la Santé et Recherche Médicale (INSERM), France.
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31
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Salakhieva DV, Sadreev II, Chen MZQ, Umezawa Y, Evstifeev AI, Welsh GI, Kotov NV. Kinetic regulation of multi-ligand binding proteins. BMC SYSTEMS BIOLOGY 2016; 10:32. [PMID: 27090530 PMCID: PMC4835871 DOI: 10.1186/s12918-016-0277-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 04/13/2016] [Indexed: 12/24/2022]
Abstract
BACKGROUND Second messengers, such as calcium, regulate the activity of multisite binding proteins in a concentration-dependent manner. For example, calcium binding has been shown to induce conformational transitions in the calcium-dependent protein calmodulin, under steady state conditions. However, intracellular concentrations of these second messengers are often subject to rapid change. The mechanisms underlying dynamic ligand-dependent regulation of multisite proteins require further elucidation. RESULTS In this study, a computational analysis of multisite protein kinetics in response to rapid changes in ligand concentrations is presented. Two major physiological scenarios are investigated: i) Ligand concentration is abundant and the ligand-multisite protein binding does not affect free ligand concentration, ii) Ligand concentration is of the same order of magnitude as the interacting multisite protein concentration and does not change. Therefore, buffering effects significantly influence the amounts of free ligands. For each of these scenarios the influence of the number of binding sites, the temporal effects on intermediate apo- and fully saturated conformations and the multisite regulatory effects on target proteins are investigated. CONCLUSIONS The developed models allow for a novel and accurate interpretation of concentration and pressure jump-dependent kinetic experiments. The presented model makes predictions for the temporal distribution of multisite protein conformations in complex with variable numbers of ligands. Furthermore, it derives the characteristic time and the dynamics for the kinetic responses elicited by a ligand concentration change as a function of ligand concentration and the number of ligand binding sites. Effector proteins regulated by multisite ligand binding are shown to depend on ligand concentration in a highly nonlinear fashion.
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Affiliation(s)
- Diana V. Salakhieva
- />Kazan (Volga Region) Federal University, 18 Kremlyovskaya St., 420008 Kazan, Russia
| | - Ildar I. Sadreev
- />Centre for Systems, Dynamics and Control, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Harrison Building, North Park Road, Exeter, EX4 4QF UK
| | - Michael Z. Q. Chen
- />Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Yoshinori Umezawa
- />Department of Dermatology, The Jikei University School of Medicine, 3-25-8 Nishishimbashi, Minato-ku, Tokyo, 105-8461 Japan
| | - Aleksandr I. Evstifeev
- />Biophysics & Bionics Lab, Institute of Physics, Kazan Federal University, Kazan, 420008 Russia
| | - Gavin I. Welsh
- />Academic Renal Unit, School of Clinical Sciences, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol, BS1 3NY UK
| | - Nikolay V. Kotov
- />Biophysics & Bionics Lab, Institute of Physics, Kazan Federal University, Kazan, 420008 Russia
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Extrapolating microdomain Ca(2+) dynamics using BK channels as a Ca(2+) sensor. Sci Rep 2016; 6:17343. [PMID: 26776352 PMCID: PMC4726033 DOI: 10.1038/srep17343] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 10/22/2015] [Indexed: 11/17/2022] Open
Abstract
Ca2+ ions play crucial roles in mediating physiological and pathophysiological processes, yet Ca2+ dynamics local to the Ca2+ source, either from influx via calcium permeable ion channels on plasmic membrane or release from internal Ca2+ stores, is difficult to delineate. Large-conductance calcium-activated K+ (BK-type) channels, abundantly distribute in excitable cells and often localize to the proximity of voltage-gated Ca2+ channels (VGCCs), spatially enabling the coupling of the intracellular Ca2+ signal to the channel gating to regulate membrane excitability and spike firing patterns. Here we utilized the sensitivity and dynamic range of BK to explore non-uniform Ca2+ local transients in the microdomain of VGCCs. Accordingly, we applied flash photolysis of caged Ca2+ to activate BK channels and determine their intrinsic sensitivity to Ca2+. We found that uncaging Ca2+ activated biphasic BK currents with fast and slow components (time constants being τf ≈ 0.2 ms and τs ≈ 10 ms), which can be accounted for by biphasic Ca2+ transients following light photolysis. We estimated the Ca2+-binding rate constant kb (≈1.8 × 108 M−1s−1) for mSlo1 and further developed a model in which BK channels act as a calcium sensor capable of quantitatively predicting local microdomain Ca2+ transients in the vicinity of VGCCs during action potentials.
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33
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Pecze L, Blum W, Schwaller B. Routes of Ca2+ Shuttling during Ca2+ Oscillations: FOCUS ON THE ROLE OF MITOCHONDRIAL Ca2+ HANDLING AND CYTOSOLIC Ca2+ BUFFERS. J Biol Chem 2015; 290:28214-28230. [PMID: 26396196 PMCID: PMC4653679 DOI: 10.1074/jbc.m115.663179] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Indexed: 01/29/2023] Open
Abstract
In some cell types, Ca2+ oscillations are strictly dependent on Ca2+ influx across the plasma membrane, whereas in others, oscillations also persist in the absence of Ca2+ influx. We observed that, in primary mesothelial cells, the plasmalemmal Ca2+ influx played a pivotal role. However, when the Ca2+ transport across the plasma membrane by the “lanthanum insulation method” was blocked prior to the induction of the serum-induced Ca2+ oscillations, mitochondrial Ca2+ transport was found to be able to substitute for the plasmalemmal Ca2+ exchange function, thus rendering the oscillations independent of extracellular Ca2+. However, in a physiological situation, the Ca2+-buffering capacity of mitochondria was found not to be essential for Ca2+ oscillations. Moreover, brief spontaneous Ca2+ changes were observed in the mitochondrial Ca2+ concentration without apparent changes in the cytosolic Ca2+ concentration, indicating the presence of a mitochondrial autonomous Ca2+ signaling mechanism. In the presence of calretinin, a Ca2+-buffering protein, the amplitude of cytosolic spikes during oscillations was decreased, and the amount of Ca2+ ions taken up by mitochondria was reduced. Thus, the increased calretinin expression observed in mesothelioma cells and in certain colon cancer might be correlated to the increased resistance of these tumor cells to proapoptotic/pronecrotic signals. We identified and characterized (experimentally and by modeling) three Ca2+ shuttling pathways in primary mesothelial cells during Ca2+ oscillations: Ca2+ shuttled between (i) the endoplasmic reticulum (ER) and mitochondria, (ii) the ER and the extracellular space, and (iii) the ER and cytoplasmic Ca2+ buffers.
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Affiliation(s)
- László Pecze
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700 Fribourg, Switzerland.
| | - Walter Blum
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700 Fribourg, Switzerland
| | - Beat Schwaller
- Anatomy, Department of Medicine, University of Fribourg, Route Albert-Gockel 1, CH-1700 Fribourg, Switzerland
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Finno CJ, Valberg SJ, Shivers J, D'Almeida E, Armién AG. Evidence of the Primary Afferent Tracts Undergoing Neurodegeneration in Horses With Equine Degenerative Myeloencephalopathy Based on Calretinin Immunohistochemical Localization. Vet Pathol 2015; 53:77-86. [PMID: 26253880 DOI: 10.1177/0300985815598787] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Equine degenerative myeloencephalopathy (EDM) is characterized by a symmetric general proprioceptive ataxia in young horses, and is likely underdiagnosed for 2 reasons: first, clinical signs overlap those of cervical vertebral compressive myelopathy; second, histologic lesions--including axonal spheroids in specific tracts of the somatosensory and motor systems--may be subtle. The purpose of this study was (1) to utilize immunohistochemical (IHC) markers to trace axons in the spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts in healthy horses and (2) to determine the IHC staining characteristics of the neurons and degenerated axons along the somatosensory tracts in EDM-affected horses. Examination of brain, spinal cord, and nerves was performed on 2 age-matched control horses, 3 EDM-affected horses, and 2 age-matched disease-control horses via IHC for calbindin, vesicular glutamate transporter 2, parvalbumin, calretinin, glutamic acid decarboxylase, and glial fibrillary acidic protein. Primary afferent axons of the spinocuneocerebellar, dorsal column-medial lemniscal, and dorsospinocerebellar tracts were successfully traced with calretinin. Calretinin-positive cell bodies were identified in a subset of neurons in the dorsal root ganglia, suggesting that calretinin IHC could be used to trace axonal projections from these cell bodies. Calretinin-immunoreactive spheroids were present in EDM-affected horses within the nuclei cuneatus medialis, cuneatus lateralis, and thoracicus. Neurons within those nuclei were calretinin negative. Cell bodies of degenerated axons in EDM-affected horses are likely located in the dorsal root ganglia. These findings support the role of sensory axonal degeneration in the pathogenesis of EDM and provide a method to highlight tracts with axonal spheroids to aid in the diagnosis of this neurodegenerative disease.
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Affiliation(s)
- C J Finno
- Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA
| | - S J Valberg
- Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA
| | - J Shivers
- Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA
| | - E D'Almeida
- Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA
| | - A G Armién
- Department of Veterinary Population Medicine, University of Minnesota, St Paul, MN, USA Veterinary Diagnostic Laboratory, University of Minnesota, St Paul, MN, USA
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Abstract
Calcium influx during action potentials triggers neurotransmitter release at presynaptic active zones. Calcium buffers limit the spread of calcium and restrict neurotransmitter release to the vicinity of calcium channels. To sustain synchronous release during repetitive activity, rapid removal of calcium from the active zone is essential, but the underlying mechanisms are unclear. Therefore, we focused on cerebellar mossy fiber synapses, which are among the fastest synapses in the mammalian brain and found very weak presynaptic calcium buffering. One might assume that strong calcium buffering has the potential to efficiently remove calcium from active zones. In contrast, our results show that weak calcium buffering speeds active zone calcium clearance. Thus, the strength of presynaptic buffering limits the rate of synaptic transmission. Fast synchronous neurotransmitter release at the presynaptic active zone is triggered by local Ca2+ signals, which are confined in their spatiotemporal extent by endogenous Ca2+ buffers. However, it remains elusive how rapid and reliable Ca2+ signaling can be sustained during repetitive release. Here, we established quantitative two-photon Ca2+ imaging in cerebellar mossy fiber boutons, which fire at exceptionally high rates. We show that endogenous fixed buffers have a surprisingly low Ca2+-binding ratio (∼15) and low affinity, whereas mobile buffers have high affinity. Experimentally constrained modeling revealed that the low endogenous buffering promotes fast clearance of Ca2+ from the active zone during repetitive firing. Measuring Ca2+ signals at different distances from active zones with ultra-high-resolution confirmed our model predictions. Our results lead to the concept that reduced Ca2+ buffering enables fast active zone Ca2+ signaling, suggesting that the strength of endogenous Ca2+ buffering limits the rate of synchronous synaptic transmission.
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Abstract
Tight coupling between Ca(2+) channels and the sensor for vesicular transmitter release at the presynaptic active zone (AZ) is crucial for high-fidelity synaptic transmission. It has been hypothesized that a switch from a loosely coupled to a tightly coupled transmission mode is a common step in the maturation of CNS synapses. However, this hypothesis has never been tested at cortical synapses. We addressed this hypothesis at a representative small cortical synapse: the synapse connecting mouse cerebellar cortical parallel fibers to Purkinje neurons. We found that the slow Ca(2+) chelator EGTA affected release significantly stronger at immature than at mature synapses, while the fast chelator BAPTA was similarly effective in both groups. Analysis of paired-pulse ratios and quantification of release probability (pr) with multiple-probability fluctuation analysis revealed increased facilitation at immature synapses accompanied by reduced pr. Cav2.1 Ca(2+) channel immunoreactivity, assessed by quantitative high-resolution immuno-electron microscopy, was scattered over immature boutons but confined to putative AZs at mature boutons. Presynaptic Ca(2+) signals were quantified with two-photon microscopy and found to be similar between maturation stages. Models adjusted to fit EGTA dose-response curves as well as differential effects of the Ca(2+) channel blocker Cd(2+) indicate looser and less homogenous coupling at immature terminals compared with mature ones. These results demonstrate functionally relevant developmental tightening of influx-release coupling at a single AZ cortical synapse and corroborate developmental tightening of coupling as a prevalent phenomenon in the mammalian brain.
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Pecze L, Schwaller B. Characterization and modeling of Ca2+ oscillations in mouse primary mesothelial cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:632-45. [DOI: 10.1016/j.bbamcr.2014.12.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 12/16/2014] [Accepted: 12/19/2014] [Indexed: 10/24/2022]
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Brachtendorf S, Eilers J, Schmidt H. A use-dependent increase in release sites drives facilitation at calretinin-deficient cerebellar parallel-fiber synapses. Front Cell Neurosci 2015; 9:27. [PMID: 25691858 PMCID: PMC4315043 DOI: 10.3389/fncel.2015.00027] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 01/15/2015] [Indexed: 12/13/2022] Open
Abstract
Endogenous Ca(2+)-binding proteins affect synaptic transmitter release and short-term plasticity (STP) by buffering presynaptic Ca(2+) signals. At parallel-fiber (PF)-to-Purkinje neuron (PN) synapses in the cerebellar cortex loss of calretinin (CR), the major buffer at PF terminals, results in increased presynaptic Ca(2+) transients and an almost doubling of the initial vesicular releases probability (p r). Surprisingly, however, it has been reported that loss of CR from PF synapses does not alter paired-pulse facilitation (PPF), while it affects presynaptic Ca(2+) signals as well as p r. Here, we addressed this puzzling observation by analyzing the frequency- and Ca(2+)-dependence of PPF at unitary PF-to-PN synapses of wild-type (WT) and CR-deficient (CR(-/-)) mice using paired recordings and computer simulations. Our analysis revealed that PPF in CR(-/-) is indeed smaller than in the WT, to a degree, however, that indicates that rapid vesicle replenishment and recruitment of additional release sites dominate the synaptic efficacy of the second response. These Ca(2+)-driven processes operate more effectively in the absence of CR, thereby, explaining the preservation of robust PPF in the mutants.
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Affiliation(s)
- Simone Brachtendorf
- Medical Faculty, Carl-Ludwig-Institute for Physiology, University of Leipzig Leipzig, Germany
| | - Jens Eilers
- Medical Faculty, Carl-Ludwig-Institute for Physiology, University of Leipzig Leipzig, Germany
| | - Hartmut Schmidt
- Medical Faculty, Carl-Ludwig-Institute for Physiology, University of Leipzig Leipzig, Germany
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Tavanti F, Pedone A, Menziani MC. A closer look into the ubiquitin corona on gold nanoparticles by computational studies. NEW J CHEM 2015. [DOI: 10.1039/c4nj01752h] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Course-grained simulations studies showed environmental-dependency of the mechanism of ubiquitin corona formation on gold nanoparticles and ubiquitin binding modalities, and a nanoparticle size-dependency of ubiquitin conformational changes and aggregation propensity.
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Affiliation(s)
- Francesco Tavanti
- Dipartimento di Scienze Chimiche e Geologiche
- Università di Modena e Reggio Emilia
- Modena
- Italy
| | - Alfonso Pedone
- Dipartimento di Scienze Chimiche e Geologiche
- Università di Modena e Reggio Emilia
- Modena
- Italy
| | - Maria Cristina Menziani
- Dipartimento di Scienze Chimiche e Geologiche
- Università di Modena e Reggio Emilia
- Modena
- Italy
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40
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Tóth K, Maglóczky Z. The vulnerability of calretinin-containing hippocampal interneurons to temporal lobe epilepsy. Front Neuroanat 2014; 8:100. [PMID: 25324731 PMCID: PMC4179514 DOI: 10.3389/fnana.2014.00100] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 09/04/2014] [Indexed: 01/21/2023] Open
Abstract
This review focuses on the vulnerability of a special interneuron type—the calretinin (CR)-containing interneurons—in temporal lobe epilepsy (TLE). CR is a calcium-binding protein expressed mainly by GABAergic interneurons in the hippocampus. Despite their morphological heterogeneity, CR-containing interneurons form a distinct subpopulation of inhibitory cells, innervating other interneurons in rodents and to some extent principal cells in the human. Their dendrites are strongly connected by zona adherentiae and presumably by gap junctions both in rats and humans. CR-containing interneurons are suggested to play a key role in the hippocampal inhibitory network, since they can effectively synchronize dendritic inhibitory interneurons. The sensitivity of CR-expressing interneurons to epilepsy was discussed in several reports, both in animal models and in humans. In the sclerotic hippocampus the density of CR-immunopositive cells is decreased significantly. In the non-sclerotic hippocampus, the CR-containing interneurons are preserved, but their dendritic tree is varicose, segmented, and zona-adherentia-type contacts can be less frequently observed among dendrites. Therefore, the dendritic inhibition of pyramidal cells may be less effective in TLE. This can be partially explained by the impairment of the CR-containing interneuron ensemble in the epileptic hippocampus, which may result in an asynchronous and thus less effective dendritic inhibition of the principal cells. This phenomenon, together with the sprouting of excitatory pathway axons and enhanced innervation of principal cells, may be involved in seizure generation. Preventing the loss of CR-positive cells and preserving the integrity of CR-positive dendrite gap junctions may have antiepileptic effects, maintaining proper inhibitory function and helping to protect principal cells in epilepsy.
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Affiliation(s)
- Kinga Tóth
- Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Hungarian Academy of Sciences Budapest, Hungary ; Institute of Experimental Medicine, Hungarian Academy of Sciences Budapest, Hungary
| | - Zsófia Maglóczky
- Institute of Experimental Medicine, Hungarian Academy of Sciences Budapest, Hungary
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41
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Filić V, Marinović M, Faix J, Weber I. The IQGAP-related protein DGAP1 mediates signaling to the actin cytoskeleton as an effector and a sequestrator of Rac1 GTPases. Cell Mol Life Sci 2014; 71:2775-85. [PMID: 24664433 PMCID: PMC11113302 DOI: 10.1007/s00018-014-1606-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 02/26/2014] [Accepted: 03/10/2014] [Indexed: 11/24/2022]
Abstract
Proteins are typically categorized into protein families based on their domain organization. Yet, evolutionarily unrelated proteins can also be grouped together according to their common functional roles. Sequestering proteins constitute one such functional class, acting as macromolecular buffers and serving as an intracellular reservoir ready to release large quantities of bound proteins or other molecules upon appropriate stimulation. Another functional protein class comprises effector proteins, which constitute essential components of many intracellular signal transduction pathways. For instance, effectors of small GTP-hydrolases are activated upon binding a GTP-bound GTPase and thereupon participate in downstream interactions. Here we describe a member of the IQGAP family of scaffolding proteins, DGAP1 from Dictyostelium, which unifies the roles of an effector and a sequestrator in regard to the small GTPase Rac1. Unlike classical effectors, which bind their activators transiently leading to short-lived signaling complexes, interaction between DGAP1 and Rac1-GTP is stable and induces formation of a complex with actin-bundling proteins cortexillins at the back end of the cell. An oppositely localized Rac1 effector, the Scar/WAVE complex, promotes actin polymerization at the cell front. Competition between DGAP1 and Scar/WAVE for the common activator Rac1-GTP might provide the basis for the oscillatory re-polarization typically seen in randomly migrating Dictyostelium cells. We discuss the consequences of the dual roles exerted by DGAP1 and Rac1 in the regulation of cell motility and polarity, and propose that similar signaling mechanisms may be of general importance in regulating spatiotemporal dynamics of the actin cytoskeleton by small GTPases.
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Affiliation(s)
- Vedrana Filić
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Maja Marinović
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Jan Faix
- Hannover Medical School, Institute for Biophysical Chemistry, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | - Igor Weber
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
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Faas GC, Mody I. Measuring the Ca²⁺-binding kinetics of proteins. Cold Spring Harb Protoc 2014; 2014:691-693. [PMID: 24987145 DOI: 10.1101/pdb.top066258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Ca(2+)-binding proteins (CBPs) are instrumental in the control of Ca(2+) signaling. For the transduction of a change in intracellular Ca(2+) concentration into a cellular biochemical or biophysical action, it is necessary for Ca(2+) to bind specific Ca(2+)-binding proteins (CBPs) that relay the Ca(2+) signal. The competition for Ca(2+) between the various CBPs plays an essential and direct role in this transduction and in the resulting biochemical message. Therefore, a thorough understanding of Ca(2+) signaling necessitates appreciating the kinetic properties of all the relevant CBPs. Unfortunately, most conventional techniques used to measure Ca(2+)-binding kinetics are too slow to determine accurately the fast binding kinetics of most CBPs. To address this problem, we have developed an ultrafast in vitro technique for measuring the Ca(2+)-binding properties of CBPs following flash photolysis of caged Ca(2+). We introduce here the protocols that are necessary for the data collection associated with this technique.
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Affiliation(s)
- Guido C Faas
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
| | - Istvan Mody
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095; Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
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Faas GC, Mody I. Measuring the steady-state properties of Ca²⁺ indicators with a set of calibrated [Ca²⁺] solutions. Cold Spring Harb Protoc 2014; 2014:758-762. [PMID: 24987134 DOI: 10.1101/pdb.prot073270] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Fluorescent Ca(2+) indicators are widely used to measure the concentration of free Ca(2+) ([Ca(2+)]free) in biological processes. By calibrating the dye under the same experimental conditions as employed during its planned use, the actual [Ca(2+)] can be calculated from the measured fluorescence. When using non ratiometric dyes, such as the Oregon Green BAPTA (OGB) family of dyes or the Fluo dyes, the steady-state affinity (K(d)) and the ratio between the maximal and minimal fluorescence (F(ratio) = F(max)/F(min)) of the particular dye are needed for this conversion. Although these values are usually given by the manufacturer, we consistently find that the actual values can differ between various batches delivered by the companies that make the dyes. In this protocol, we provide the recipe for a series of solutions with a known and tightly buffered [Ca(2+)](free) and describe how to use these mixtures to determine the exact K(d) and F(ratio) of a fluorescent Ca(2+) dye.
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Affiliation(s)
- Guido C Faas
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
| | - Istvan Mody
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095; Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
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Abstract
Fluorescent Ca(2+) indicators are widely used to measure the concentration of free Ca(2+) ([Ca(2+)](free)) in biological processes. To determine the exact kinetics of changes in [Ca(2+)](free) and the processes underlying these changes (e.g., Ca(2+) binding to Ca(2+)-binding proteins), it is necessary to know the exact binding properties of the indicator used. Here, we describe how to determine the binding rate constants (k(on) and k(off)) of Ca(2+) indicators.
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Affiliation(s)
- Guido C Faas
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
| | - Istvan Mody
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095; Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
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Faas GC, Mody I. Collecting data to determine the Ca²⁺-binding properties of DM-nitrophen and proteins. Cold Spring Harb Protoc 2014; 2014:768-73. [PMID: 24987136 DOI: 10.1101/pdb.prot073296] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Conventional techniques used to measure Ca(2+) binding are too slow to determine accurately the fast binding kinetics of most molecules such as Ca(2+)-binding proteins (CBPs). We have developed an ultra-fast in vitro technique for measuring the Ca(2+)-binding properties of CBPs following flash photolysis of caged Ca(2+). Although the details of the setup, the mathematics, and the analysis involved in this technique have been published elsewhere, many of the practical details regarding the actual measurements have, until now, only been described minimally. Here, we present a protocol to gather the data necessary to determine the kinetic properties of a caged-Ca(2+) compound and a CBP.
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Affiliation(s)
- Guido C Faas
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
| | - Istvan Mody
- Department of Neurology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095; Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, California 90095
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Ma J, Yao XH, Fu Y, Yu YC. Development of Layer 1 Neurons in the Mouse Neocortex. Cereb Cortex 2014; 24:2604-18. [DOI: 10.1093/cercor/bht114] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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Tuckwell HC, Penington NJ. Computational modeling of spike generation in serotonergic neurons of the dorsal raphe nucleus. Prog Neurobiol 2014; 118:59-101. [PMID: 24784445 DOI: 10.1016/j.pneurobio.2014.04.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 04/14/2014] [Accepted: 04/21/2014] [Indexed: 01/14/2023]
Abstract
Serotonergic neurons of the dorsal raphe nucleus, with their extensive innervation of limbic and higher brain regions and interactions with the endocrine system have important modulatory or regulatory effects on many cognitive, emotional and physiological processes. They have been strongly implicated in responses to stress and in the occurrence of major depressive disorder and other psychiatric disorders. In order to quantify some of these effects, detailed mathematical models of the activity of such cells are required which describe their complex neurochemistry and neurophysiology. We consider here a single-compartment model of these neurons which is capable of describing many of the known features of spike generation, particularly the slow rhythmic pacemaking activity often observed in these cells in a variety of species. Included in the model are 11 kinds of ion channels: a fast sodium current INa, a delayed rectifier potassium current IKDR, a transient potassium current IA, a slow non-inactivating potassium current IM, a low-threshold calcium current IT, two high threshold calcium currents IL and IN, small and large conductance potassium currents ISK and IBK, a hyperpolarization-activated cation current IH and a leak current ILeak. In Sections 3-8, each current type is considered in detail and parameters estimated from voltage clamp data where possible. Three kinds of model are considered for the BK current and two for the leak current. Intracellular calcium ion concentration Cai is an additional component and calcium dynamics along with buffering and pumping is discussed in Section 9. The remainder of the article contains descriptions of computed solutions which reveal both spontaneous and driven spiking with several parameter sets. Attention is focused on the properties usually associated with these neurons, particularly long duration of action potential, steep upslope on the leading edge of spikes, pacemaker-like spiking, long-lasting afterhyperpolarization and the ramp-like return to threshold after a spike. In some cases the membrane potential trajectories display doublets or have humps or notches as have been reported in some experimental studies. The computed time courses of IA and IT during the interspike interval support the generally held view of a competition between them in influencing the frequency of spiking. Spontaneous activity was facilitated by the presence of IH which has been found in these neurons by some investigators. For reasonable sets of parameters spike frequencies between about 0.6Hz and 1.2Hz are obtained, but frequencies as high as 6Hz could be obtained with special parameter choices. Topics investigated and compared with experiment include shoulders, notches, anodal break phenomena, the effects of noradrenergic input, frequency versus current curves, depolarization block, effects of cell size and the effects of IM. The inhibitory effects of activating 5-HT1A autoreceptors are also investigated. There is a considerable discussion of in vitro versus in vivo firing behavior, with focus on the roles of noradrenergic input, corticotropin-releasing factor and orexinergic inputs. Location of cells within the nucleus is probably a major factor, along with the state of the animal.
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Affiliation(s)
- Henry C Tuckwell
- Max Planck Institute for Mathematics in the Sciences, Inselstr. 22, 04103 Leipzig, Germany; School of Electrical and Electronic Engineering, University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Nicholas J Penington
- Department of Physiology and Pharmacology, State University of New York, Downstate Medical Center, Box 29, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA; Program in Neural and Behavioral Science and Robert F. Furchgott Center for Neural and Behavioral Science, State University of New York, Downstate Medical Center, Box 29, 450 Clarkson Avenue, Brooklyn, NY 11203-2098, USA
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48
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Vyleta NP, Jonas P. Loose Coupling Between Ca2+ Channels and Release Sensors at a Plastic Hippocampal Synapse. Science 2014; 343:665-70. [DOI: 10.1126/science.1244811] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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49
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Schwaller B. Calretinin: from a "simple" Ca(2+) buffer to a multifunctional protein implicated in many biological processes. Front Neuroanat 2014; 8:3. [PMID: 24550787 PMCID: PMC3913827 DOI: 10.3389/fnana.2014.00003] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 01/19/2014] [Indexed: 12/30/2022] Open
Abstract
The hexa-EF-hand Ca(2+)-binding protein calretinin (CR) is predominantly expressed in specific neurons of the central and peripheral nervous system. However, CR expression is also observed in non-neuronal cells, e.g., during embryonic development and in mesothelioma cells. Of the 6 EF-hand domains, 5 are functional; the first 4 domains form 2 pairs showing high cooperativity within a pair that results in non-linear modulation of intracellular Ca(2+) signals by CR. EF-hand domain 5 has a low affinity and represents the identified interaction site with CR-binding partners present in mouse cerebellar granule cells. CR binding to other targets including the pore-forming α1 subunit of the Ca(2+) channel Ca V 2.1, as well as to huntingtin indicates additional Ca(2+) sensor functions besides the well-known Ca(2+)-buffering functions. The absence of CR in cerebellar granule cells of CR(-/-) mice results in increased excitability and altered firing of Purkinje cells and promotes cerebellar 160-Hz oscillations impairing motor coordination. The putative role of CR in neuroprotection is still highly discussed. Altogether, CR emerges as a multi-functional protein also associated with development, i.e., cell proliferation, differentiation, and cell death.
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Affiliation(s)
- Beat Schwaller
- Anatomy, Department of Medicine, University of FribourgFribourg, Switzerland
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50
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Zakowski W, Bogus-Nowakowska K, Robak A. Embryonic and postnatal development of calcium-binding proteins immunoreactivity in the anterior thalamus of the guinea pig. J Chem Neuroanat 2013; 53:25-32. [PMID: 24060609 DOI: 10.1016/j.jchemneu.2013.09.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 08/20/2013] [Accepted: 09/15/2013] [Indexed: 10/26/2022]
Abstract
Our recent studies have shown that the distribution of calretinin (CR) in the anterior thalamic nuclei (ATN) changes significantly during the development of the guinea pig. The present study was designed to reveal the distribution pattern of calcium-binding proteins, i.e. calbindin (CB) and parvalbumin (PV), as well as the colocalization pattern of all three proteins, including CR, in the ATN of guinea pigs ranging from the 40th embryonic day (E40) to the 80th postnatal day (P80). According to these patterns, CB appears exclusively in the perikarya of the anteromedial nucleus (AM) not before P20 and always colocalizes with CR. Moreover, CB and CR colocalize in fibers of thin bundles traversing the anteroventral nucleus (AV) since E50. The ATN also display CB-positive neuropil in all studied stages, especially a strong one in the ventral part of the AV. PV was not observed in the perikarya of the ATN in all the stages, but was abundantly present in the neuropil of the anterodorsal nucleus (AD). No colocalizations exist between PV and the rest of the studied proteins. In conclusion, our study reveals that the distribution of the studied proteins differs greatly. Nevertheless, the postnatal coexistence of CB and CR in the AM perikarya may indicate the cooperation of both of the proteins in some functions of the nucleus. Parvalbumin is limited mostly to the neuropil of the AD, suggesting different functions in comparison to CB and CR.
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Affiliation(s)
- Witold Zakowski
- Department of Comparative Anatomy, Faculty of Biology and Biotechnology, University of Warmia and Mazury in Olsztyn, Pl. Łódzki 3, 10-727 Olsztyn, Poland.
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