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Sen A, Hongpaisan J, Wang D, Nelson TJ, Alkon DL. Protein Kinase Cϵ (PKCϵ) Promotes Synaptogenesis through Membrane Accumulation of the Postsynaptic Density Protein PSD-95. J Biol Chem 2016; 291:16462-76. [PMID: 27330081 DOI: 10.1074/jbc.m116.730440] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Indexed: 11/06/2022] Open
Abstract
Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the detailed mechanisms by which PKCϵ induces synaptogenesis are not fully understood. Accumulation of PSD-95 to the postsynaptic density (PSD) is known to lead to synaptic maturation and strengthening of excitatory synapses. Here we investigated the relationship between PKCϵ and PSD-95. We show that the PKCϵ activators dicyclopropanated linoleic acid methyl ester and bryostatin 1 induce phosphorylation of PSD-95 at the serine 295 residue, increase the levels of PSD-95, and enhance its membrane localization. Elimination of the serine 295 residue in PSD-95 abolished PKCϵ-induced membrane accumulation. Knockdown of either PKCϵ or JNK1 prevented PKCϵ activator-mediated membrane accumulation of PSD-95. PKCϵ directly phosphorylated PSD-95 and JNK1 in vitro Inhibiting PKCϵ, JNK, or calcium/calmodulin-dependent kinase II activity prevented the effects of PKCϵ activators on PSD-95 phosphorylation. Increase in membrane accumulation of PKCϵ and phosphorylated PSD-95 (p-PSD-95(S295)) coincided with an increased number of synapses and increased amplitudes of excitatory post-synaptic potentials (EPSPs) in adult rat hippocampal slices. Knockdown of PKCϵ also reduced the synthesis of PSD-95 and the presynaptic protein synaptophysin by 30 and 44%, respectively. Prolonged activation of PKCϵ increased synapse number by 2-fold, increased presynaptic vesicle density, and greatly increased PSD-95 clustering. These results indicate that PKCϵ promotes synaptogenesis by activating PSD-95 phosphorylation directly through JNK1 and calcium/calmodulin-dependent kinase II and also by inducing expression of PSD-95 and synaptophysin.
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Affiliation(s)
- Abhik Sen
- From the Blanchette Rockefeller Neurosciences Institute, Morgantown, West Virginia 26505
| | - Jarin Hongpaisan
- From the Blanchette Rockefeller Neurosciences Institute, Morgantown, West Virginia 26505
| | - Desheng Wang
- From the Blanchette Rockefeller Neurosciences Institute, Morgantown, West Virginia 26505
| | - Thomas J Nelson
- From the Blanchette Rockefeller Neurosciences Institute, Morgantown, West Virginia 26505
| | - Daniel L Alkon
- From the Blanchette Rockefeller Neurosciences Institute, Morgantown, West Virginia 26505
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Chataigner L, Guo J, Erskine PT, Coker AR, Wood SP, Gombos Z, Cooper JB. Binding of Gd(3+) to the neuronal signalling protein calexcitin identifies an exchangeable Ca(2+)-binding site. Acta Crystallogr F Struct Biol Commun 2016; 72:276-81. [PMID: 27050260 PMCID: PMC4822983 DOI: 10.1107/s2053230x16003526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 02/29/2016] [Indexed: 11/11/2022] Open
Abstract
Calexcitin was first identified in the marine snail Hermissenda crassicornis as a neuronal-specific protein that becomes upregulated and phosphorylated in associative learning. Calexcitin possesses four EF-hand motifs, but only the first three (EF-1 to EF-3) are involved in binding metal ions. Past work has indicated that under physiological conditions EF-1 and EF-2 bind Mg(2+) and Ca(2+), while EF-3 is likely to bind only Ca(2+). The fourth EF-hand is nonfunctional owing to a lack of key metal-binding residues. The aim of this study was to use a crystallographic approach to determine which of the three metal-binding sites of calexcitin is most readily replaced by exogenous metal ions, potentially shedding light on which of the EF-hands play a `sensory' role in neuronal calcium signalling. By co-crystallizing recombinant calexcitin with equimolar Gd(3+) in the presence of trace Ca(2+), EF-1 was shown to become fully occupied by Gd(3+) ions, while the other two sites remain fully occupied by Ca(2+). The structure of the Gd(3+)-calexcitin complex has been refined to an R factor of 21.5% and an Rfree of 30.4% at 2.2 Å resolution. These findings suggest that EF-1 of calexcitin is the Ca(2+)-binding site with the lowest selectivity for Ca(2+), and the implications of this finding for calcium sensing in neuronal signalling pathways are discussed.
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Affiliation(s)
- Lucas Chataigner
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
| | - Jingxu Guo
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
| | - Peter T. Erskine
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
- Department of Biological Sciences, Birkbeck, University of London, Malet Street, Bloomsbury, London WC1E 7HX, England
| | - Alun R. Coker
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
| | - Steve P. Wood
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
| | - Zoltan Gombos
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Jonathan B. Cooper
- Division of Medicine, UCL, Gower Street, London WC1E 6BT, England
- Department of Biological Sciences, Birkbeck, University of London, Malet Street, Bloomsbury, London WC1E 7HX, England
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Alkon DL, Epstein H, Kuzirian A, Bennett MC, Nelson TJ. Protein synthesis required for long-term memory is induced by PKC activation on days before associative learning. Proc Natl Acad Sci U S A 2005; 102:16432-7. [PMID: 16258064 PMCID: PMC1283453 DOI: 10.1073/pnas.0508001102] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2005] [Indexed: 11/18/2022] Open
Abstract
Protein synthesis has long been known to be required for associative learning to consolidate into long-term memory. Here we demonstrate that PKC isozyme activation on days before training can induce the synthesis of proteins necessary and sufficient for subsequent long-term memory consolidation. Bryostatin (Bryo), a macrolide lactone with efficacy in subnanomolar concentrations and a potential therapeutic for Alzheimer's disease, is a potent activator of PKC, some of whose isozymes undergo prolonged activation after associative learning. Under normal conditions, two training events with paired visual and vestibular stimuli cause short-term memory of the mollusc Hermissenda that lasts approximately 7 min. However, after 4-h exposures to Bryo (0.25 ng/ml) on two preceding days, the same two training events produced long-term conditioning that lasted >1 week and that was not blocked by anisomycin (1 mug/ml). Anisomycin, however, eliminated long-term memory lasting at least 1 week after nine training events. Both the nine training events alone and two Bryo exposures plus two training event regimens caused comparably increased levels of the PKC alpha-isozyme substrate calexcitin in identified type B neurons and enhanced PKC activity in the membrane fractions. Furthermore, Bryo increased overall protein synthesis in cultured mammalian neurons by up to 60% for >3 days. The specific PKC antagonist Ro-32-0432 blocked much of this Bryo-induced protein synthesis as well as the Bryo-induced enhancement of the behavioral conditioning. Thus, Bryo-induced PKC activation produces those proteins necessary and sufficient for long-term memory on days in advance of the training events themselves.
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Affiliation(s)
- Daniel L Alkon
- Blanchette Rockefeller Neurosciences Institute, 9601 Medical Center Drive, Rockville, MD 20850-3332, USA.
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4
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Beaven GDE, Erskine PT, Wright JN, Mohammed F, Gill R, Wood SP, Vernon J, Giese KP, Cooper JB. Crystallization and preliminary X-ray diffraction analysis of calexcitin from Loligo pealei: a neuronal protein implicated in learning and memory. Acta Crystallogr Sect F Struct Biol Cryst Commun 2005; 61:879-81. [PMID: 16511184 PMCID: PMC1991304 DOI: 10.1107/s1744309105026758] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 08/22/2005] [Indexed: 11/10/2022]
Abstract
The neuronal protein calexcitin from the long-finned squid Loligo pealei has been expressed in Escherichia coli and purified to homogeneity. Calexcitin is a 22 kDa calcium-binding protein that becomes up-regulated in invertebrates following Pavlovian conditioning and is likely to be involved in signal transduction events associated with learning and memory. Recombinant squid calexcitin has been crystallized using the hanging-drop vapour-diffusion technique in the orthorhombic space group P2(1)2(1)2(1). The unit-cell parameters of a = 46.6, b = 69.2, c = 134.8 A suggest that the crystals contain two monomers per asymmetric unit and have a solvent content of 49%. This crystal form diffracts X-rays to at least 1.8 A resolution and yields data of high quality using synchrotron radiation.
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Affiliation(s)
- G. D. E. Beaven
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - P. T. Erskine
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - J. N. Wright
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - F. Mohammed
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - R. Gill
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - S. P. Wood
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
| | - J. Vernon
- Wolfson Institute for Biomedical Research, University College London, Cruciform Building, Gower Street, London WC1E 6BT, England
| | - K. P. Giese
- Wolfson Institute for Biomedical Research, University College London, Cruciform Building, Gower Street, London WC1E 6BT, England
| | - J. B. Cooper
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, England
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Nelson TJ, Zhao WQ, Yuan S, Favit A, Pozzo-Miller L, Alkon DL. Calexcitin interaction with neuronal ryanodine receptors. Biochem J 1999; 341 ( Pt 2):423-33. [PMID: 10393102 PMCID: PMC1220376 DOI: 10.1042/0264-6021:3410423] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Calexcitin (CE), a Ca2+- and GTP-binding protein, which is phosphorylated during memory consolidation, is shown here to co-purify with ryanodine receptors (RyRs) and bind to RyRs in a calcium-dependent manner. Nanomolar concentrations of CE released up to 46% of the 45Ca label from microsomes preloaded with 45CaCl2. This release was Ca2+-dependent and was blocked by antibodies against the RyR or CE, by the RyR inhibitor dantrolene, and by a seven-amino-acid peptide fragment corresponding to positions 4689-4697 of the RyR, but not by heparin, an Ins(1,4,5)P3-receptor antagonist. Anti-CE antibodies, in the absence of added CE, also blocked Ca2+ release elicited by ryanodine, suggesting that the CE and ryanodine binding sites were in relative proximity. Calcium imaging with bis-fura-2 after loading CE into hippocampal CA1 pyramidal cells in hippocampal slices revealed slow, local calcium transients independent of membrane depolarization. Calexcitin also released Ca2+ from liposomes into which purified RyR had been incorporated, indicating that CE binding can be a proximate cause of Ca2+ release. These results indicated that CE bound to RyRs and suggest that CE may be an endogenous modulator of the neuronal RyR.
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Affiliation(s)
- T J Nelson
- Laboratory of Adaptive Systems, National Institutes of Health, Bldg. 36, Room 4A-23, Bethesda, MD 20892, USA.
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Sun MK, Nelson TJ, Xu H, Alkon DL. Calexcitin transformation of GABAergic synapses: from excitation filter to amplifier. Proc Natl Acad Sci U S A 1999; 96:7023-8. [PMID: 10359832 PMCID: PMC22042 DOI: 10.1073/pnas.96.12.7023] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Encoding an experience into a lasting memory is thought to involve an altered operation of relevant synapses and a variety of other subcellular processes, including changed activity of specific proteins. Here, we report direct evidence that co-applying (associating) membrane depolarization of rat hippocampal CA1 pyramidal cells with intracellular microinjections of calexcitin (CE), a memory-related signaling protein, induces a long-term transformation of inhibitory postsynaptic potentials from basket interneurons (BAS) into excitatory postsynaptic potentials. This synaptic transformation changes the function of the synaptic inputs from excitation filter to amplifier, is accompanied by a shift of the reversal potential of BAS-CA1 postsynaptic potentials, and is blocked by inhibiting carbonic anhydrase or antagonizing ryanodine receptors. Effects in the opposite direction are produced when anti-CE antibody is introduced into the cells, whereas heat-inactivated CE and antibodies are ineffective. These data suggest that CE is actively involved in shaping BAS-CA1 synaptic plasticity and controlling information processing through the hippocampal networks.
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Affiliation(s)
- M K Sun
- Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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Cammarota M, Paratcha G, Levi de Stein M, Bernabeu R, Izquierdo I, Medina JH. B-50/GAP-43 phosphorylation and PKC activity are increased in rat hippocampal synaptosomal membranes after an inhibitory avoidance training. Neurochem Res 1997; 22:499-505. [PMID: 9130262 DOI: 10.1023/a:1027324214060] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Several lines of evidence indicate that protein kinase C (PKC) is involved in long-term potentiation (LTP) and in certain forms of learning. Recently, we found a learning-specific, time-dependent increase in [3H]phorbol dibutyrate binding to membrane-associated PKC in the hippocampus of rats subjected to an inhibitory avoidance task. Here we confirm and extend this observation, describing that a one trial inhibitory avoidance learning was associated with rapid and specific increases in B-50/GAP-43 phosphorylation in vitro and in PKC activity in hippocampal synaptosomal membranes. The increased phosphorylation of B-50/GAP-43, was seen at 30 min (+35% relative to naive or shocked control groups), but not at 10 or 60 min after training. This learning-associated increase in the phosphorylation of B-50/GAP-43 is mainly due to an increase in the activity of PKC. This is based on three different sets of data: 1) PKC activity increased by 24% in hippocampal synaptosomal membranes of rats sacrificed 30 min after training; 2) B-50/GAP-43 immunoblots revealed no changes in the amount of this protein among the different experimental groups; 3) phosphorylation assays, performed in the presence of bovine purified PKC or in the presence of the selective PKC inhibitor CGP 41231, exhibited no differences in B-50/GAP-43 phosphorylation between naive and trained animals. In conclusion, these results support the contention that hippocampal PKC participates in the early neural events of memory formation of an aversively-motivated learning task.
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Affiliation(s)
- M Cammarota
- Instituto de Biología Celular y Neurociencias, Facultad de Medicina, UBA, Buenos Aires, Argentina
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Abstract
Apart from their primary function as balance sensors, Hermissenda hair cells are presynaptic neurons involved in the Ca(2+)-dependent neuronal plasticity in postsynaptic B photoreceptors that accompanies classical conditioning. With a view to beginning to understand presynaptic mechanisms of plasticity in the vestibulo-visual system, a locus for conditioning-induced neuronal plasticity, outward currents that may govern the excitability of hair cells were recorded by means of a whole-cell patch-clamp technique. Three K+ currents were characterized: a 4-aminopyridine-sensitive transient outward K+ current (IA), a tetraethyl ammonium-sensitive delayed rectifier K+ current (IK,V), and a Ca(2+)-activated K+ current (IK,Ca). IA activates and decays rapidly; the steady-state activation and inactivation curves of the current reveal a window current close to the apparent resting voltage of the hair cells, suggesting that the current is partially activated at rest. By modulating firing frequency and perhaps damping membrane oscillations, IA may regulate synaptic release at baseline. In contrast, IK,V and IK,Ca have slow onset and exhibit little or no inactivation. These two K+ currents may determine the duration of the repolarization phase of hair-cell action potentials and hence synaptic release via Ca2+ influx through voltage-gated Ca2+ channels. In addition, IK,Ca may be responsible for the afterhyperpolarization of hair cell membrane voltage following prolonged stimulation.
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Affiliation(s)
- E N Yamoah
- Department of Physiology, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
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Nelson TJ, Cavallaro S, Yi CL, McPhie D, Schreurs BG, Gusev PA, Favit A, Zohar O, Kim J, Beushausen S, Ascoli G, Olds J, Neve R, Alkon DL. Calexcitin: a signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability. Proc Natl Acad Sci U S A 1996; 93:13808-13. [PMID: 8943017 PMCID: PMC19433 DOI: 10.1073/pnas.93.24.13808] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
A previously uncharacterized 22-kDa Ca(2+)-binding protein that also binds guanosine nucleotides was characterized, cloned, and analyzed by electrophysiological techniques. The cloned protein, calexcitin, contains two EF-hands and also has homology with GTP-binding proteins in the ADP ribosylation factor family. In addition to binding two molecules of Ca2+, calexcitin bound GTP and possessed GTPase activity. Calexictin is also a high affinity substrate for protein kinase C. Application of calexcitin to the inner surface of inside-out patches of human fibroblast membranes, in the presence of Ca2+ and the absence of endogenous Ca2+/calmodulin kinase type II or protein kinase C activity, reduced the mean open time and mean open probability of 115 +/- 6 pS K+ channels. Calexcitin thus appears to directly regulate K+ channels. When microinjected into molluscan neurons or rabbit cerebellar Purkinje cell dendrites, calexcitin was highly effective in enhancing membrane excitability. Because calexcitin translocates to the cell membrane after phosphorylation, calexcitin could serve as a Ca(2+)-activated signaling molecule that increases cellular excitability, which would in turn increase Ca2+ influx through the membrane. This is also the first known instance of a GTP-binding protein that binds Ca2+.
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Affiliation(s)
- T J Nelson
- Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Pivovarov AS. Activators of G-proteins increase the plasticity of cholinoreceptors of common snail neurons. NEUROSCIENCE AND BEHAVIORAL PHYSIOLOGY 1996; 26:73-9. [PMID: 8801472 DOI: 10.1007/bf02391158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The influences of depth of damping of the inward current evoked by acetylcholine (the ACh-current), of two nonhydrolyzable analogs of GTP, which irreversibly activate G-proteins, namely 5'-guanylylimidodiphosphate (Gpp(NH)p) and guanosine 5'-O-(3-thiotriphosphate) (GTP-g-S), were investigated in identified RPa3 and LPa3 neurons of the common snail using the two-electrode voltage clamp technique. An irreversible deepening of the damping of the ACh-current following intracellular iontophoretic injections (-2 nA, 10 min) of Gpp(NH)p and GTP-g-S was demonstrated. A conclusion was reached regarding the participation of G-proteins in the molecular mechanism of the positive regulation of plasticity of cholinoreceptor neurons. Both of the G-protein activators used demonstrated a new atypical influence on the damping of the ACh-current, a disruption of its monotonic character. The hypothesis is advanced that the cause of such an influence lies in the oscillations of the concentration of intracellular Ca2+ induced by G-protein activators.
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Nelson TJ, Yoshioka T, Toyoshima S, Han YF, Alkon DL. Characterization of a GTP-binding protein implicated in both memory storage and interorganelle vesicle transport. Proc Natl Acad Sci U S A 1994; 91:9287-91. [PMID: 7937757 PMCID: PMC44797 DOI: 10.1073/pnas.91.20.9287] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The phosphorylation state of cp20, a low molecular weight GTP-binding protein that is a high-affinity substrate for protein kinase C, was previously shown to change after associative conditioning of molluscs and mammals and to induce many of the biophysical and structural modifications that accompany memory retention. Here, cp20 was purified from squid optic lobes and biochemically characterized. A monoclonal antibody prepared against squid cp20 reacted with Hermissenda cp20 and a 20-kDa protein in rabbit hippocampus, while a polyclonal antibody also cross-reacted with Sar1p and ADP-ribosylation factor (ARF). A partial peptide sequence of squid cp20 was 50% identical (23/46 amino acids) with Sar1p, a yeast GTP-binding protein involved in vesicle transport, indicating that cp20 is probably a new member of the ARF family. This classification is consistent with our recent demonstration that cp20 affects retrograde movement of intraaxonal organelles or particles and suggests a possible role for particle traffic between intraneuronal organelles in memory acquisition.
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Affiliation(s)
- T J Nelson
- Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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12
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Sakakibara M, Ikeno H, Usui S, Collin C, Alkon DL. Reconstruction of ionic currents in a molluscan photoreceptor. Biophys J 1993; 65:519-27. [PMID: 8369456 PMCID: PMC1225744 DOI: 10.1016/s0006-3495(93)81068-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Two-microelectrode voltage-clamp measurements were made to determine the kinetics and voltage dependence of ionic currents across the soma membrane of the Hermissenda type B photoreceptor. The voltage-dependent outward potassium currents, IA and ICa(2+)-K+, the inward voltage-dependent calcium current, ICa2+ and the light-induced current, IIgt, were then described with Hodgkin-Huxley-type equations. The fast-activating and inactivating potassium current, IA, was described by the equation; IA(t) = gA(max)(ma infinity[1-exp(-t/tau ma)])3 x (ha infinity [1-exp(-t/tau ha)] + exp(-t/tau ha)) (Vm-EK), where the parameters ma infinity, ha infinity, tau ma, and tau ha are functions of membrane potential, Vm, and ma infinity and ha infinity are steady-state activation and inactivation parameters. Similarly, the calcium-dependent outward potassium current, ICa(2+)-K+, was described by the equation, ICa(2+)-K+ (t) = gc(max)(mc infinity(VC)(1-exp[-t/tau mc (VC)]))pc (hc infinity(VC) [1-exp(-t/tau hc)] + exp(-t/tau hc(VC)])pc(VC-EK). In high external potassium, ICa(2+)-K+ could be measured in approximate isolation from other currents as a voltage-dependent inward tail current following a depolarizing command pulse from a holding potential of -60 mV. A voltage-dependent inward calcium current across the type B soma membrane, ICa2+, activated rapidly, showed little inactivation, and was described by the equation: ICa2+ = gCa(max) [1 + exp](-Vm-5)/7]-1 (Vm-ECa), where gCa(max) was 0.5 microS. The light-induced current with both fast and slow phases was described by: IIgt(t) = IIgt1 + IIgt2 + IIgt3, IIgti = gIgti [1-exp(- ton/tau mi)] exp(-ton/tau hi)(Vm-EIgti) (i = 1, 2). For i = 3, /Igt(t) = gigt3m33h3(Vm - Eigt3)exp(-ton/Ton) x exp(-tfoff/t Off). Based on these reconstructions of ionic currents, learning-induced enhancement of the long lasting depolarization (LLD) of the photoreceptor'slight response was shown to arise from progressive inactivation of /A, lca2+ -K+, and lCa2+.
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Affiliation(s)
- M Sakakibara
- Department of Biological Science and Technology, School of High Tecnology for Human Welfare, Tokai University, Shizuoka, Japan
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Höpp HP, Alkon DL. Different ionic conductances are modulated during the late receptor potential and the prolonged depolarizing afterpotential in Hermissenda type A photoreceptors. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 1993; 172:47-55. [PMID: 8445579 DOI: 10.1007/bf00214714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Wavelength-dependent, bistable phenomena were found in the receptor potential of Hermissenda crassicornis type A photoreceptors. Short exposure to blue light induced a prolonged depolarizing afterpotential (PDA) following the cessation of the light stimulus. Stronger adaptation to blue light, as caused by prolonged exposure and/or high intensity stimulation, effected a reduction in the early depolarizing transient of the late receptor potential (LRP) as elicited by subsequent stimuli. Vast separation of LRP emergence and PDA emergence could be obtained in photoreceptors in which a strong cancellation of the LRP was accomplished but a PDA still emerged after cessation of the light stimulus. Short exposure to yellow light cancelled the PDA, and stronger adaptation restored the LRP (opposite effect to blue light). The initial depolarizing part of the LRP had earlier been demonstrated to be mediated by the light-dependent increase of an inward conductance. In contrast, in this study the PDA was found to be accompanied by the reduction of an outward conductance, most likely a K+ conductance. A bistable photopigment system is thought to control the bistable receptor potential phenomenology by regulating the different membrane conductances during the LRP and the PDA.
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Affiliation(s)
- H P Höpp
- National Institute of Neural Disorders and Stroke, Bethesda, MD 20892
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14
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Collin C, Papageorge AG, Sakakibara M, Huddie PL, Lowy DR, Alkon DL. Early regulation of membrane excitability by ras oncogene proteins. Biophys J 1990; 58:785-90. [PMID: 2207264 PMCID: PMC1281019 DOI: 10.1016/s0006-3495(90)82421-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Two electrode voltage clamp conditions were used to study the early effects on ionic membrane channels of the intracellularly injected proto-oncogenic form of c-Ha-ras (c-ras) and its oncogenic counterpart v-Ha-ras (v-ras). These experiments were conducted on isolated somata of identified fully differentiated neurons of the sea snail Hermissenda. 20 min after c-ras, and 10 min after v-ras intracellular injections into type B medial photoreceptors of Hermissenda, the peak amplitude of two outward potassium currents (IA and IC), across the isolated Type B soma membrane begin to decrease. These two currents have been previously isolated by differences in activation and inactivation kinetics and their response to pharmacological blockers. c- or v-ras injections did not have any effect on a voltage-dependent inward calcium current. Reduction of IA preceded that of IC. Current reductions due to c-ras, but not to v-ras injection reversed spontaneously after 40 min. The voltage dependence of the steady state inactivation of IA shifted toward more negative potentials with ras injections. Ras-mediated cell transformations therefore, could involve, perhaps as initial events, prolonged modification of membrane currents.
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Affiliation(s)
- C Collin
- National Institutes of Health, Laboratory of Molecular and Cellular Neurobiology, Bethesda, Maryland 20892
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