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Machado I, Gonzalez PV, Vilcaes A, Carniglia L, Schiöth HB, Lasaga M, Scimonelli TN. Interleukin-1β-induced memory reconsolidation impairment is mediated by a reduction in glutamate release and zif268 expression and α-melanocyte-stimulating hormone prevented these effects. Brain Behav Immun 2015; 46:137-46. [PMID: 25637483 DOI: 10.1016/j.bbi.2015.01.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Revised: 12/26/2014] [Accepted: 01/17/2015] [Indexed: 01/31/2023] Open
Abstract
The immune system is an important modulator of learning, memory and neural plasticity. Interleukin 1β (IL-1β), a pro-inflammatory cytokine, significantly affects several cognitive processes. Previous studies by our group have demonstrated that intrahippocampal administration of IL-1β impairs reconsolidation of contextual fear memory. This effect was reversed by the melanocortin alpha-melanocyte-stimulating hormone (α-MSH). The mechanisms underlying the effect of IL-1β on memory reconsolidation have not yet been established. Therefore, we examined the effect of IL-1β on glutamate release, ERK phosphorylation and the activation of the transcription factor zinc finger- 268 (zif268) during reconsolidation. Our results demonstrated that IL-1β induced a significant decrease of glutamate release after reactivation of the fear memory and this effect was related to calcium concentration in hippocampal synaptosomes. IL-1β also reduced ERK phosphorylation and zif268 expression in the hippocampus. Central administration of α-MSH prevented the decrease in glutamate release, ERK phosphorylation and zif268 expression induced by IL-1β. Our results establish possible mechanisms involved in the detrimental effect of IL-1β on memory reconsolidation and also indicate that α-MSH may exert a beneficial modulatory role in preventing IL-1β effects.
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Affiliation(s)
- Ivana Machado
- IFEC-CONICET, Depto. Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina
| | - Patricia V Gonzalez
- IFEC-CONICET, Depto. Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina
| | - Alejandro Vilcaes
- CIQUIBIC-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina
| | - Lila Carniglia
- Instituto de Investigaciones Biomédicas INBIOMED UBA-CONICET, Facultad de Medicina, Buenos Aires, Argentina
| | - Helgi B Schiöth
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Uppsala, Sweden
| | - Mercedes Lasaga
- Instituto de Investigaciones Biomédicas INBIOMED UBA-CONICET, Facultad de Medicina, Buenos Aires, Argentina
| | - Teresa N Scimonelli
- IFEC-CONICET, Depto. Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
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HARTZELL HCRISS, DUCHATELLE-GOURDON ISABELLE. Structure and Neural Modulation of Cardiac Calcium Channels. J Cardiovasc Electrophysiol 2013. [DOI: 10.1111/j.1540-8167.1992.tb01937.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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3
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Parekh AB. Ca2+ microdomains near plasma membrane Ca2+ channels: impact on cell function. J Physiol 2008; 586:3043-54. [PMID: 18467365 PMCID: PMC2538792 DOI: 10.1113/jphysiol.2008.153460] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Accepted: 05/07/2008] [Indexed: 12/21/2022] Open
Abstract
In eukaryotic cells, a rise in cytoplasmic Ca(2+) can activate a plethora of responses that operate on time scales ranging from milliseconds to days. Inherent to the use of a promiscuous signal like Ca(2+) is the problem of specificity: how can Ca(2+) activate some responses but not others? We now know that the spatial profile of the Ca(2+) signal is important Ca(2+) does not simply rise uniformly throughout the cytoplasm upon stimulation but can reach very high levels locally, creating spatial gradients. The most fundamental local Ca(2+) signal is the Ca(2+) microdomain that develops rapidly near open plasmalemmal Ca(2+) channels like voltage-gated L-type (Cav1.2) and store-operated CRAC channels. Recent work has revealed that Ca(2+) microdomains arising from these channels are remarkably versatile in triggering a range of responses that differ enormously in both temporal and spatial profile. Here, I delineate basic features of Ca(2+) microdomains and then describe how these highly local signals are used by Ca(2+)-permeable channels to drive cellular responses.
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Affiliation(s)
- Anant B Parekh
- Department of Physiology, Anatomy and Genetics, Oxford University, Parks Road, Oxford OX1 3PT, UK.
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4
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Erxleben C, Liao Y, Gentile S, Chin D, Gomez-Alegria C, Mori Y, Birnbaumer L, Armstrong DL. Cyclosporin and Timothy syndrome increase mode 2 gating of CaV1.2 calcium channels through aberrant phosphorylation of S6 helices. Proc Natl Acad Sci U S A 2006; 103:3932-7. [PMID: 16537462 PMCID: PMC1533789 DOI: 10.1073/pnas.0511322103] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Calcium channels in the plasma membrane rarely remain open for much more than a millisecond at any one time, which avoids raising intracellular calcium to toxic levels. However, the dihydropyridine-sensitive calcium channels of the CaV1 family, which selectively couple electrical excitation to endocrine secretion, cardiovascular contractility, and neuronal transcription, have a unique second mode of gating, "mode 2," that involves frequent openings of much longer duration. Here we report that two human conditions, cyclosporin neurotoxicity and Timothy syndrome, increase mode 2 gating of the recombinant rabbit CaV1.2 channel. In each case, mode 2 gating depends on a Ser residue at the cytoplasmic end of the S6 helix in domain I (Ser-439, Timothy syndrome) or domain IV (Ser-1517, cyclosporin). Both Ser reside in consensus sequences for type II calmodulin-dependent protein kinase. Pharmacologically inhibiting type II calmodulin-dependent protein kinase or mutating the Ser residues to Ala prevents the increase in mode 2 gating. We propose that aberrant phosphorylation, or "phosphorylopathy," of the CaV1.2 channel protein contributes to the excitotoxicity associated with Timothy syndrome and with chronic cyclosporin treatment of transplant patients.
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Affiliation(s)
| | - Yanhong Liao
- Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709; and
| | | | | | - Claudio Gomez-Alegria
- Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709; and
| | - Yasuo Mori
- National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
| | - Lutz Birnbaumer
- Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709; and
- To whom correspondence may be addressed. E-mail:
| | - David L. Armstrong
- Laboratories of *Neurobiology and
- To whom correspondence may be addressed. E-mail:
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Hui K, Gardzinski P, Sun HS, Backx PH, Feng ZP. Permeable ions differentially affect gating kinetics and unitary conductance of L-type calcium channels. Biochem Biophys Res Commun 2005; 338:783-92. [PMID: 16243294 DOI: 10.1016/j.bbrc.2005.10.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Accepted: 10/04/2005] [Indexed: 11/24/2022]
Abstract
Although ion permeation and gating of L-type Ca(2+) channels are generally considered separate processes controlled by distinct components of the channel protein, ion selectivity can vary with the kinetic state. To test this possibility, we studied single-channel currents (cell-attached) of recombinant L-type channels (Ca(V)1.2, beta(2a), and alpha(2)delta) transiently expressed in tsA201 cells in the presence of the channel agonist BayK 8644 which promotes long channel openings (Mode 2 openings). We found that both the brief (Mode 1) and long (Mode 2) mean open times in the presence of Ca(2+) were relatively longer than those with Ba(2+). The unitary slope conductance with Ba(2+) was significantly larger (p<0.05) in Mode 2 openings than for brief Mode 1 openings, whereas the conductance with Ca(2+) did not vary with mode gating. Consequently, the gamma(Ba):gamma(Ca) ratio was greater for Mode 2 than Mode 1 openings. Our findings indicate that both ion permeation and gating kinetics of the L-type channel are differentially modulated by permeable ions. Ca(2+) binding to the L-type channel may stabilize the alteration of channel ion permeability mediated by gating kinetics, and thus, play a role in preventing excessive ion entry when the activation gating of the channel is promoted to the prolonged open state.
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Affiliation(s)
- Kwokyin Hui
- Department of Physiology, University of Toronto, Toronto, Ont., Canada M5S 1A8
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6
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Erxleben C, Gomez-Alegria C, Darden T, Mori Y, Birnbaumer L, Armstrong DL. Modulation of cardiac Ca(V)1.2 channels by dihydropyridine and phosphatase inhibitor requires Ser-1142 in the domain III pore loop. Proc Natl Acad Sci U S A 2003; 100:2929-34. [PMID: 12601159 PMCID: PMC151443 DOI: 10.1073/pnas.2628046100] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/31/2002] [Indexed: 11/18/2022] Open
Abstract
Dihydropyridine-sensitive, voltage-activated calcium channels respond to membrane depolarization with two distinct modes of activity: short bursts of very short openings (mode 1) or repetitive openings of much longer duration (mode 2). Here we show that both the dihydropyridine, BayK8644 (BayK), and the inhibitor of SerThr protein phosphatases, okadaic acid, have identical effects on the gating of the recombinant cardiac calcium channel, Ca(V)1.2 (alpha(1)C). Each produced identical mode 2 gating in cell-attached patches, and each prevented rundown of channel activity when the membrane patch was excised into ATP-free solutions. These effects required Ser or Thr at position 1142 in the domain III pore loop between transmembrane segments S5 and S6, where dihydropyridines bind to the channel. Mutation of Ser-1142 to Ala or Cys produced channels with very low activity that could not be modulated by either BayK or okadaic acid. A molecular model of Ca(V)1.2 indicates that Ser-1142 is unlikely to be phosphorylated, and thus we conclude that BayK binding stabilizes mode 2 gating allosterically by either protecting a phospho Ser/Thr on the alpha(1)C subunit or mimicking phosphorylation at that site.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Adenosine Triphosphate/metabolism
- Animals
- Calcium Channel Agonists/pharmacology
- Calcium Channels/metabolism
- Calcium Channels, L-Type/metabolism
- Calcium Channels, L-Type/physiology
- Cell Line
- Cell Membrane/metabolism
- Cricetinae
- Dihydropyridines/pharmacology
- Electrophysiology
- Enzyme Inhibitors/pharmacology
- Models, Molecular
- Mutagenesis, Site-Directed
- Mutation
- Okadaic Acid/pharmacology
- Phosphoric Monoester Hydrolases/antagonists & inhibitors
- Phosphorylation
- Protein Binding
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Rabbits
- Serine/chemistry
- Threonine/chemistry
- Time Factors
- Transfection
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Affiliation(s)
- Christian Erxleben
- Laboratory of Signal Transduction and Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA
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7
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Ramakrishnan NA, Green GE, Pasha R, Drescher MJ, Swanson GS, Perin PC, Lakhani RS, Ahsan SF, Hatfield JS, Khan KM, Drescher DG. Voltage-gated Ca2+ channel Ca(V)1.3 subunit expressed in the hair cell epithelium of the sacculus of the trout Oncorhynchus mykiss: cloning and comparison across vertebrate classes. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2002; 109:69-83. [PMID: 12531517 DOI: 10.1016/s0169-328x(02)00522-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Full-length sequence (>6.5 kb) has been determined for the Ca(V)1.3 pore-forming subunit of the voltage-gated Ca(2+) channel from the saccular hair cells of the rainbow trout (Oncorhynchus mykiss). Primary structure was obtained from overlapping PCR and cloned fragments, amplified by primers based on teleost, avian, and mammalian sources. Trout saccular Ca(V)1.3 was localized to hair cells, as evidenced by its isolation from an epithelial layer in which the hair cell is the only intact cell type. The predicted amino acid sequence of the trout hair cell Ca(V)1.3 is approximately 70% identical to the sequences of avian and mammalian Ca(V)1.3 subunits and shows L-type characteristics. The trout hair cell Ca(V)1.3 expresses a 26-aa insert in the I-II cytoplasmic loop (exon 9a) and a 10-aa insert in the IVS2-IVS3 cytoplasmic loop (exon 30a), neither of which is appreciably represented in trout brain. The exon 9a insert also occurs in hair cell organs of chick and rat, and appears as an exon in human genomic Ca(V)1.3 sequence (but not in the Ca(V)1.3 coding sequence expressed in human brain or pancreas). The exon 30a insert, although expressed in hair cells of chick as well as trout, does not appear in comparable rat or human tissues. Further, the IIIS2 region shows a splice choice (exon 22a) that is associated with the hair cell organs of trout, chick, and rat, but is not found in human genomic sequence. The elucidation of the primary structure of the voltage-gated Ca(2+) channel Ca(V)1.3 subunit from hair cells of the teleost, representing the lowest of the vertebrate classes, suggests a generality of sensory mechanism for Ca(V)1.3 across hair cell systems. In particular, the exon 9a insert of this channel appears to be the molecular feature most consistently associated with hair cells from fish to mammal, consonant with the hypothesis that the latter region may be a signature for the hair cell.
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Affiliation(s)
- Neeliyath A Ramakrishnan
- Laboratory of Bio-otology, Department of Otolaryngology, Wayne State University School of Medicine, 259 Lande Medical Research Building, 540 East Canfield Avenue, Detroit, MI 48201, USA
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8
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Dzhura I, Wu Y, Colbran RJ, Corbin JD, Balser JR, Anderson ME. Cytoskeletal disrupting agents prevent calmodulin kinase, IQ domain and voltage-dependent facilitation of L-type Ca2+ channels. J Physiol 2002; 545:399-406. [PMID: 12456820 PMCID: PMC2290681 DOI: 10.1113/jphysiol.2002.021881] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A calmodulin (CaM) binding 'IQ' domain on the L-type Ca(2+) channel (LTCC) C terminus and calmodulin kinase II (CaMK) both signal increases in LTCC opening probability (P(o)) by shifting LTCCs into a gating mode (mode 2) with long openings through a process called facilitation. However, the mechanism whereby CaMK and the IQ domain are targeted to LTCCs is unknown. Endogenous CaMK is targeted to LTCCs in excised cell membrane patches because LTCC P(o) increased significantly in CaM-enriched (20 microM) bath solution and this effect was prevented by a specific CaMK inhibitory peptide, but not by an inactive control peptide. Pre-exposure of myocytes to the cytoskeletal disrupting agents nocodazole (microtubule specific) or cytochalasin D (microfilament specific) prevented the effects of CaM-dependent increases in P(o) of LTCCs in excised membrane patches. Neither cytochalasin D nor nocodazole altered the distribution of LTCC gating modes under basal conditions in on-cell mode or excised cell membrane patches, but each of these agents occluded the response of LTCCs to exogenous, constitutively active CaMK and to an IQ-mimetic peptide (IQmp). Cytochalasin D and nocodazole pretreatment also prevented LTCC facilitation that followed a cell membrane depolarizing prepulse. In contrast, cytochalasin D and nocodazole did not affect the increase in LTCC P(o) or prevent the shift to mode 2 gating in response to protein kinase A, indicating that cytoskeletal disruption specifically prevents prepulse, CaMK and IQ-dependent LTCC facilitation.
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Affiliation(s)
- Igor Dzhura
- Department of Internal Medicine, Vanderbilt University Medical Center, Vanderbilt University, Nashville, TN 37232-6300, USA
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9
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Day M, Olson PA, Platzer J, Striessnig J, Surmeier DJ. Stimulation of 5-HT(2) receptors in prefrontal pyramidal neurons inhibits Ca(v)1.2 L type Ca(2+) currents via a PLCbeta/IP3/calcineurin signaling cascade. J Neurophysiol 2002; 87:2490-504. [PMID: 11976386 DOI: 10.1152/jn.00843.2001] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
There is growing evidence linking alterations in serotonergic signaling in the prefrontal cortex to the etiology of schizophrenia. Prefrontal pyramidal neurons are richly innervated by serotonergic fibers and express high levels of serotonergic 5-HT(2)-class receptors. It is unclear, however, how activation of these receptors modulates cellular activity. To help fill this gap, whole cell voltage-clamp and single-cell RT-PCR studies of acutely isolated layer V-VI prefrontal pyramidal neurons were undertaken. The vast majority (>80%) of these neurons had detectable levels of 5-HT(2A) or 5-HT(2C) receptor mRNA. Bath application of 5-HT(2) agonists inhibited voltage-dependent Ca(2+) channel currents. L-type Ca(2+) channels were a particularly prominent target of this signaling pathway. The L-type channel modulation was blocked by disruption of G(alphaq) signaling or by inhibition of phospholipase Cbeta. Antagonism of intracellular inositol trisphosphate signaling, chelation of intracellular Ca(2+), or depletion of intracellular Ca(2+) stores also blocked this modulation. Inhibition of the Ca(2+)-dependent phosphatase calcineurin prevented receptor-mediated modulation of L-type currents. Last, the 5-HT(2) receptor modulation was robustly expressed in neurons from Ca(v)1.3 knockout mice. These findings argue that 5-HT(2) receptors couple through G(alphaq) proteins to trigger a phospholipase Cbeta/inositol trisphosphate signaling cascade resulting in the mobilization of intracellular Ca(2+), activation of calcineurin, and inhibition of Ca(v)1.2 L-type Ca(2+) currents. This modulation and its blockade by atypical neuroleptics could have wide-ranging effects on synaptic integration and long-term gene expression in deep-layer prefrontal pyramidal neurons.
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MESH Headings
- Animals
- Calcineurin/metabolism
- Calcium/metabolism
- Calcium Channels, L-Type/metabolism
- Calcium Channels, N-Type/metabolism
- Calcium Channels, R-Type/metabolism
- GTP-Binding Protein alpha Subunits, Gq-G11
- Gene Expression/physiology
- Heterotrimeric GTP-Binding Proteins/metabolism
- Inositol Phosphates/metabolism
- Isoenzymes/genetics
- Isoenzymes/metabolism
- Patch-Clamp Techniques
- Phospholipase C beta
- Prefrontal Cortex/cytology
- Prefrontal Cortex/physiology
- Pyramidal Cells/physiology
- RNA, Messenger/analysis
- Rats
- Rats, Sprague-Dawley
- Receptor, Serotonin, 5-HT2A
- Receptor, Serotonin, 5-HT2B
- Receptors, Serotonin/genetics
- Receptors, Serotonin/metabolism
- Signal Transduction/physiology
- Type C Phospholipases/genetics
- Type C Phospholipases/metabolism
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Affiliation(s)
- Michelle Day
- Department of Physiology/Northwestern University Institute for Neuroscience, Northwestern University Medical School, Chicago, Illinois 60611, USA
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10
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Abstract
Ca2+ entry (I(Ca)) through cardiac L-type Ca2+ channels (LTCC) drives critical cellular processes ranging from contraction to gene expression, and, when disordered, is implicated in arrhythmias and hypertrophy. LTCC activation occurs by cell membrane depolarization, but LTCCs are also regulated by auxiliary proteins, phosphorylation, and intracellular CA2+([Ca2+]i). LTCC regulation by [Ca2+]i is especially intriguing because increased [Ca2+]i signals dual and conflicting commands for I(Ca)inactivation and facilitation. A recent explosion of work has shed new light on the mechanisms and molecular identity of domains necessary for [Ca2+]i-dependent regulation of LTCC.
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Affiliation(s)
- M E Anderson
- Department of Internal Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
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11
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Abstract
Voltage-gated Ca(2+) channels mediate Ca(2+) entry into cells in response to membrane depolarization. Electrophysiological studies reveal different Ca(2+) currents designated L-, N-, P-, Q-, R-, and T-type. The high-voltage-activated Ca(2+) channels that have been characterized biochemically are complexes of a pore-forming alpha1 subunit of approximately 190-250 kDa; a transmembrane, disulfide-linked complex of alpha2 and delta subunits; an intracellular beta subunit; and in some cases a transmembrane gamma subunit. Ten alpha1 subunits, four alpha2delta complexes, four beta subunits, and two gamma subunits are known. The Cav1 family of alpha1 subunits conduct L-type Ca(2+) currents, which initiate muscle contraction, endocrine secretion, and gene transcription, and are regulated primarily by second messenger-activated protein phosphorylation pathways. The Cav2 family of alpha1 subunits conduct N-type, P/Q-type, and R-type Ca(2+) currents, which initiate rapid synaptic transmission and are regulated primarily by direct interaction with G proteins and SNARE proteins and secondarily by protein phosphorylation. The Cav3 family of alpha1 subunits conduct T-type Ca(2+) currents, which are activated and inactivated more rapidly and at more negative membrane potentials than other Ca(2+) current types. The distinct structures and patterns of regulation of these three families of Ca(2+) channels provide a flexible array of Ca(2+) entry pathways in response to changes in membrane potential and a range of possibilities for regulation of Ca(2+) entry by second messenger pathways and interacting proteins.
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Affiliation(s)
- W A Catterall
- Department of Pharmacology, Box 357280, University of Washington, Seattle, Washington 98195-7280, USA.
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12
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D2 dopamine receptors in striatal medium spiny neurons reduce L-type Ca2+ currents and excitability via a novel PLC[beta]1-IP3-calcineurin-signaling cascade. J Neurosci 2001. [PMID: 11124974 DOI: 10.1523/jneurosci.20-24-08987.2000] [Citation(s) in RCA: 347] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In spite of the recognition that striatal D(2) receptors are critical determinants in a variety of psychomotor disorders, the cellular mechanisms by which these receptors shape neuronal activity have remained a mystery. The studies presented here reveal that D(2) receptor stimulation in enkephalin-expressing medium spiny neurons suppresses transmembrane Ca(2+) currents through L-type Ca(2+) channels, resulting in diminished excitability. This modulation is mediated by G(beta)(gamma) activation of phospholipase C, mobilization of intracellular Ca(2+) stores, and activation of the calcium-dependent phosphatase calcineurin. In addition to providing a unifying mechanism to explain the apparently divergent effects of D(2) receptors in striatal medium spiny neurons, this novel signaling linkage provides a foundation for understanding how this pivotal receptor shapes striatal excitability and gene expression.
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13
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Huang Y, Takahashi M, Tanzawa K, Putney JW. Effect of adenophostin A on Ca2+ entry and calcium release-activated calcium current (Icrac) in rat basophilic leukemia cells. J Biol Chem 1998; 273:31815-21. [PMID: 9822648 DOI: 10.1074/jbc.273.48.31815] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In most non-excitable cells, calcium influx is signaled by depletion of intracellular calcium stores, a process known as capacitative calcium entry. Adenophostin A, a potent activator of the inositol 1, 4,5-trisphosphate receptor, has been reported to activate Ca2+ entry in Xenopus oocytes to a greater extent than expected on the basis of its ability to release calcium stores. In this study, we compared the abilities of adenophostin A and inositol 2,4,5-trisphosphate ((2, 4,5)IP3) to release Ca2+ from intracellular stores, to activate Ca2+ entry, and to activate calcium release-activated calcium current (Icrac) in rat basophilic leukemia cells. Under conditions of low intracellular Ca2+ buffering (0.1 mM BAPTA), adenophostin A-induced Ca2+ release and activation of Icrac could be monitored simultaneously. However, other reagents that would be expected to deplete Ca2+ stores ((2,4,5)IP3, 3-fluoro-inositol 1,4, 5-trisphosphate, thapsigargin, and ionomycin) were unable to activate Icrac under this low Ca2+ buffering condition. Adenophostin A activated Icrac after a significant delay, longer than the delay for Ca2+ release. Thus, adenophostin A activates Icrac as a consequence of release of intracellular Ca2+, rather than directly acting on store-operated channels. The unique ability of adenophostin A to activate Icrac under conditions of low intracellular Ca2+ buffering suggests an additional site of action, perhaps in preventing or reducing rapid Ca2+-dependent inactivation of store-operated Ca2+ channels.
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Affiliation(s)
- Y Huang
- Calcium Regulation Section, Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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14
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Heidelberger R. Adenosine triphosphate and the late steps in calcium-dependent exocytosis at a ribbon synapse. J Gen Physiol 1998; 111:225-41. [PMID: 9450941 PMCID: PMC2222770 DOI: 10.1085/jgp.111.2.225] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The ATP dependence of the kinetics of Ca2+-dependent exocytosis after flash photolysis of caged Ca2+ was studied by capacitance measurements with submillisecond resolution in single synaptic terminals of retinal bipolar neurons. After control experiments verified that this combination of techniques is valid for the study of exocytosis in synaptic terminals, a comparison was made between the Ca2+ dependence of the rate of exocytosis in synaptic terminals internally dialyzed with MgATP, MgATP-gamma-S, or no added Mg2+ or nucleotide. The Ca2+ threshold for release, the maximum rate of release, and the overall relationship between the rate of synaptic vesicle fusion and [Ca2+]i were found to be independent of MgATP. A decrease in the average rate at near-threshold [Ca2+]i was observed in terminals with MgATP-gamma-S, but due to the small sample size is of unclear significance. The Ca2+ dependence of the delay between the elevation of [Ca2+]i and the beginning of the capacitance rise was also found to be independent of MgATP. In contrast, MgATP had a marked effect on the ability of terminals to respond to multiple stimuli. Terminals with MgATP typically exhibited a capacitance increase to a second stimulus that was >70% of the amplitude of the first response and to a third stimulus with a response amplitude that was >50% of the first, whereas terminals without MgATP responded to a second stimulus with a response <35% of the first and rarely responded to a third flash. These results suggest a major role for MgATP in preparing synaptic vesicles for fusion, but indicate that cytosolic MgATP may have little role in events downstream of calcium entry, provided that [Ca2+]i near release sites is elevated above approximately 30 microM.
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Affiliation(s)
- R Heidelberger
- Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
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15
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Erxleben C, Rathmayer W. A dihydropyridine-sensitive voltage-dependent calcium channel in the sarcolemmal membrane of crustacean muscle. J Gen Physiol 1997; 109:313-26. [PMID: 9089439 PMCID: PMC2217073 DOI: 10.1085/jgp.109.3.313] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/1996] [Accepted: 11/29/1996] [Indexed: 02/04/2023] Open
Abstract
Single-channel currents through calcium channels in muscle of a marine crustacean, the isopod Idotea baltica, were investigated in cell-attached patches. Inward barium currents were strongly voltage-dependent, and the channels were closed at the cell's resting membrane potential. The open probability (Po) increased e-fold for an 8.2 mV (+/- 2.4, n = 13) depolarization. Channel opening were mainly brief (< 0.3 ms) and evenly distributed throughout 100-ms pulses. Averaged, quasimacroscopic currents showed fast activation and deactivation and did not inactivate during 100-ms test pulses. Similarly, channel activity persisted at steadily depolarized holding potentials. With 200 mM Ba2+ as charge carrier, the average slope conductance from the unitary currents between +30 and +80 mV, was 20 pS (+/- 2.6, n = 12). The proportion of long openings, which were very infrequent under control conditions, was greatly increased by preincubation of the muscle fibers with the calcium channel agonist, the dihydropyridine Bay K8644 (10-100 microM). Properties of these currents resemble those through the L-type calcium channels of mammalian nerve, smooth muscle, and cardiac muscle cells.
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Affiliation(s)
- C Erxleben
- Department of Biology, University of Konstanz, Germany.
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16
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Abstract
Since 1975, endocrine pituitary cells have been known to be excitable neuronlike cells. Using powerful single-cell approaches, in particular the patch clamp electrophysiological recording technique and the monitoring of Ca(2+) with fluorescent probes, solid evidence has been provided in the last 10 years that intracellular Ca(2+) signals are produced by stimulators and inhibitors of secretion via the modulation of action potentials in isolated pituitary cells. As cytosolic Ca(2+) changes are thought to control numerous cellular functions (for example, secretion, protein synthesis, gene expression, and proliferation) over a long time scale-milliseconds to hours-it is now time to address the long-standing question of what functions would be physiologically controlled by electrical excitability in intact pituitary tissue.
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Affiliation(s)
- P Mollard
- Patrice Mollard is at INSERM Unité 401, Pharmacologie Moléculaire de Récepteurs d'Hormones Peptidiques, CCIPE, 141 Rue de la Cardonille, 34094 Montpellier, Cedex 05 France
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17
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Abstract
Voltage-activated calcium (Ca2+) influx is increased in mammalian CA1 hippocampal neurons during aging. However, the molecular basis for this elevation is not known. The partially dissociated hippocampal ("zipper") slice preparation was used to analyze single Ca2+ channel activity in CA1 neurons of adult and aged rats. Total L-type Ca2+ channel activity in patches was found to increase with aging, primarily because of an increase in the density of functional channels. Learning in aged animals was inversely correlated with channel density. This increase in functional Ca2+ channels with aging could underlie the vulnerability of neurons to age-associated neurodegenerative conditions.
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Affiliation(s)
- O Thibault
- Department of Pharmacology, College of Medicine, University of Kentucky, Lexington 40536-0084, USA
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18
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Dreijer AMC, Verheule S, Kits KS. Inhibition of a slowly inactivating high-voltage-activated calcium current by the neuropeptide FMRFa in molluscan neuroendocrine cells. INVERTEBRATE NEUROSCIENCE 1995. [DOI: 10.1007/bf02331834] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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19
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Stapleton SR, Bell BA, Wootton JF, Scott RH. Modulation of Ca(2+)-dependent currents in metabolically stressed cultured sensory neurones by intracellular photorelease of ATP. Br J Pharmacol 1995; 114:544-50. [PMID: 7881754 PMCID: PMC1510228 DOI: 10.1111/j.1476-5381.1995.tb13261.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
1. The whole cell recording technique was used to study high voltage-activated Ca2+ currents and Ca(2+)-activated Cl- tail currents from cultured neonatal dorsal root ganglion neurones of the rat which were metabolically stressed. The neurones were metabolically stressed with 2-deoxy-D-glucose (5 mM) for 30 min to 3 h. The aim of the project was to examine the actions of intracellular photorelease of ATP on the properties of Ca(2+)-dependent currents and determine if the effects of metabolic stress could be reversed. 2. The mean duration of Ca(2+)-activated Cl- tail currents was significantly increased by metabolic stress and this effect was reversed by intracellular photorelease of approximately 300 microM ATP. Intracellular photolysis of 'caged' photolabile compounds was achieved with a xenon flash lamp. 3. Intracellular photorelease of ATP and adenosine 3':5'-cyclic monophosphate (cyclic AMP) (about 40 microM) also accelerated the inactivation of high voltage-activated Ca2+ currents evoked by 500 ms depolarizing step commands from -90 mV to 0 mV. This effect was prevented by intracellular application of the calcineurin (protein phosphatase-2B) inhibitor cyclosporin A (14 nM) and cyclophilin A (50 nM) either applied together or individually. In contrast the protein phosphatase 1 and 2A inhibitor, calyculin A, increased voltage-activated Ca2+ currents, but failed to prevent enhanced inactivation induced by intracellular photorelease of ATP. Intracellular photorelease of ATP had no effect on Ca2+ currents recorded from control neurones which were not metabolically stressed and supplied with glucose and ATP in the extracellular and patch pipette solutions respectively. 4. In conclusion, intracellular photorelease of ATP increases the decay of Ca2+-activated Cl- tail currents in metabolically stressed neurones suggesting that the efficiency of intracellular Ca2+ buffering was improved. Additionally, an ATP/cyclic AMP-dependent component of high voltage-activated Ca2+current inactivation which is mediated by calcineurin is revealed following photolysis of 'caged' ATP or cyclic AMP in metabolically stressed neurones.
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Affiliation(s)
- S R Stapleton
- Department of Physiology, St George's Hospital Medical School, London
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20
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Campbell DL, Strauss HC. Regulation of calcium channels in the heart. ADVANCES IN SECOND MESSENGER AND PHOSPHOPROTEIN RESEARCH 1995; 30:25-88. [PMID: 7695992 DOI: 10.1016/s1040-7952(05)80004-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- D L Campbell
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710
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21
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Galli A, DeFelice LJ. Inactivation of L-type Ca channels in embryonic chick ventricle cells: dependence on the cytoskeletal agents colchicine and taxol. Biophys J 1994; 67:2296-304. [PMID: 7696470 PMCID: PMC1225614 DOI: 10.1016/s0006-3495(94)80715-5] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
This article shows that colchicine and taxol strongly influence the kinetics of L-type Ca channels in intact cardiac cells, and it suggests a mechanism for this action. It is known that colchicine disassociates microtubules into tubulin, and that taxol stabilizes microtubules. We have found that colchicine increases the probability that Ca channels are in the closed state and that taxol increases the probability they are in the open state. Moreover, taxol lengthens the mean open time of Ca channels. In this regard, taxol is similar to Bay-K 8644; however, Bay K works on inside-out patches, but taxol does not. Neither colchicine nor taxol alters the number of Ca channels in a patch. We have quantified these results as follows. It is known that L-type channels in embryonic chick heart ventricle cells have voltage- and current-dependent inactivation. In 10 mM Ba, channel conductance is linear in the range -10 to 20 mV. The conductance is 12 +/- 1 pS, and the extrapolated reversal potential is 42 +/- 2 mV (n = 3). In cell-attached patches, inactivation depends on the number of channels. One channel (holding at -80 mV and stepping to 0 mV for 500 ms) shows virtually no inactivation. However, three channels inactivate with a time constant of 360 +/- 20 ms (n = 6). In similar patches, colchicine (80 microM for 15 min) decreases the inactivation time constant to 162 +/- 33 ms (n = 4) and taxol (50 microM for 10 min) virtually abolishes inactivation (time constant 812 +/- 265 ms (n = 4)). We suggest that colchicine and taxol affect Ca channels through their action on the cytoskeleton, which in turn regulates the effective concentration of inactivating ions near the mouths of channels. An alternate explanation is that free tubulin interacts directly with Ca channels.
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Affiliation(s)
- A Galli
- Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322
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22
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Cytosolic Ca2+ of excitable pituitary cells at resting potentials is controlled by steady state Ca2+ currents sensitive to dihydropyridines. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)31511-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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23
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Stelzer A, Shi H. Impairment of GABAA receptor function by N-methyl-D-aspartate-mediated calcium influx in isolated CA1 pyramidal cells. Neuroscience 1994; 62:813-28. [PMID: 7870309 DOI: 10.1016/0306-4522(94)90479-0] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Mechanisms of regulation of GABAA receptor function by intracellular calcium ([Ca2+]i) were examined in cell somata and apical dendrites of pyramidal cells, acutely dissociated from the CA1 hippocampal subfield of adult guinea-pigs. GABAA receptor-mediated currents were measured by whole-cell clamp recordings. N-methyl-D-aspartate receptor-mediated currents were used as conditioning source of calcium influx. Peak amplitudes of somatic GABAA whole-cell currents were reduced to about 15% of control values when net inward charge accumulation by N-methyl-D-aspartate currents reached 1.85 nC. A similar decline of GABAA currents was observed in dendritic recordings. The N-methyl-D-aspartate-mediated reduction of somatic and dendritic GABAA currents was accompanied by a well correlated decrease in peak and chord conductances. Pharmacological blockade of N-methyl-D-aspartate currents by 2-amino-5-phosphonopentanoic acid prevented the N-methyl-D-aspartate-mediated suppression of GABAA responses. The N-methyl-D-aspartate effect was mediated by the calcium component of N-methyl-D-aspartate receptor-mediated currents as demonstrated by a lack of effect in the absence of extracellular calcium and faster N-methyl-D-aspartate-mediated suppression of GABAA responses in lower intracellular 1,2-bis(2-aminophenoxy)ethane-N,N,N',N"-tetra-acetate. N-methyl-D-aspartate-mediated suppression of GABAA currents was significantly less expressed when intracellular ATP was replaced by its analog adenosine 5'-O-(3-thiotriphosphate) and when the specific phosphatase 2B inhibitor cypermethrin was added intracellularly. The reduction of GABAA responses persisted after cessation of N-methyl-D-aspartate-mediated calcium influx, indicating a long-term action of N-methyl-D-aspartate on GABAA responses. Voltage-activated calcium currents did not affect GABAA responses under the experimental conditions applied. In conclusion, the data presented show that calcium influxes through N-methyl-D-aspartate receptor channels result in long-term suppression of GABAA receptor function in CA1 pyramidal cells. Intracellular mechanisms of N-methyl-D-aspartate-mediated reduction of GABAA conductances involve activation of phosphatase 2B and consecutive dephosphorylation of the GABAA receptor or a closely associated GABAA receptor-regulating enzyme. Possible mechanisms of such a distinct N-methyl-D-aspartate-dependent calcium signalling pathway in the dephosphorylation-dependent suppression or GABAA receptor function are discussed.
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Affiliation(s)
- A Stelzer
- Department of Pharmacology, State University of New York, Brooklyn 11203
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24
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Plomp JJ, van Kempen GT, Molenaar PC. The upregulation of acetylcholine release at endplates of alpha-bungarotoxin-treated rats: its dependency on calcium. J Physiol 1994; 478 ( Pt 1):125-36. [PMID: 7965828 PMCID: PMC1155651 DOI: 10.1113/jphysiol.1994.sp020236] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
1. The presynaptic component of an adaptive feedback mechanism leading to increased acetylcholine (ACh) release was studied in endplates of diaphragms from rats treated chronically with alpha-bungarotoxin (alpha BTX). 2. Quantal contents were calculated 'directly' from the amplitude of miniature endplate potentials (MEPPs) and endplate potentials (EPPs) which were recorded after mu-conotoxin treatment to prevent muscle action potentials. 3. In vitro application of the Ca2+ channel blockers nifedipine (10 microM) or omega-conotoxin (40 nM) had no significant effect on the increased quantal content of endplates from alpha BTX-treated rats. 4. At control endplates, in vitro block of presynaptic K+ channels by 5 microM 3,4-diaminopyridine did increase the quantal content to a level which was similar to that found in endplates of alpha BTX-treated rats but also induced a broadening of EPPs, which was not found at endplates after alpha BTX treatment. 5. The difference between quantal contents of alpha BTX-treated and control rats was highly dependent on the [Ca2+]o/[Mg2+]o ratio when [Mg2+]o was fixed at 1 mM. At low [Ca2+]o, the quantal content of endplates from alpha BTX-treated rats was lower than that of controls while at [Ca2+]o in the normal and high range this was reversed. However, changing the [Ca2+]o/[Mg2+]o ratio by means of [Mg2+]o, at a fixed [Ca2+]o of 2 mM, did not influence the relative increase of quantal contents at endplates from alpha BTX-treated rats. Double logarithmic plots of the 'toxin-induced' myasthenia gravis (TIMG) and control quantal content versus [Ca2+]o had an approximately linear part between 0.2 and 1.5 mM [Ca2+]o. The slopes of the TIMG and control lines were 1.81 and 0.96, indicating that the ACh release in TIMG muscles was more sensitive to changes of [Ca2+]o than controls. 6. At normal [Ca2+]o and [Mg2+]o, the depression of EPP amplitude during stimulation of the phrenic nerve at 30-50 Hz was somewhat larger at endplates from alpha BTX-treated rats than at control endplates. At low [Ca2+]o, the potentiation of EPP amplitudes during a stimulus train was much larger at endplates from alpha BTX-treated rats than from controls. 7. The results do not support the idea that the increased release of ACh is caused via regulatory effects on the presynaptic Ca2+ or K+ channels. Instead, the anomalous dependency of ACh release on Ca2+ in muscles of alpha BTX-treated rats suggests that a cytoplasmic, Ca(2+)-dependent, component is involved in the adaptive change of transmitter release.
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Affiliation(s)
- J J Plomp
- Department of Physiology, University of Leiden, The Netherlands
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25
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Bielefeldt K, Jackson MB. Intramolecular and intermolecular enzymatic modulation of ion channels in excised membrane patches. Biophys J 1994; 66:1904-14. [PMID: 7521226 PMCID: PMC1275916 DOI: 10.1016/s0006-3495(94)80984-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
A calcium-activated potassium channel in posterior pituitary nerve terminals was modulated by phosphorylation and dephosphorylation. Nearly every patch of membrane containing this channel also contained both membrane bound protein phosphatase and membrane-bound protein kinase. By examining the statistical and kinetic nature of phosphorylation and dephosphorylation in excised patches, it was possible to evaluate two contrasting models for these enzymatic reactions. One of these models treated catalysis as an intermolecular process in which the enzyme and substrate are separate molecular species that diffuse and encounter one another during collisions. The second model treated catalysis as an intramolecular process in which the enzyme and substrate reside within a stable macromolecular complex. The study began with a Poisson analysis of the distribution of channel number in patches, and of the number of protein phosphatase-free and protein kinase-free patches. Subsequent kinetic analysis of dephosphorylation yielded an estimate of the mean number of protein phosphatase molecules per patch that was similar to the value obtained from Poisson analysis. Because these two estimates were independent predictions based on the intermolecular model, their agreement supported this model. Analysis of channel number in protein phosphatase-free patches and of the rarity of patches showing partial but incomplete rundown provided additional support for the intermolecular model over the intramolecular model. Furthermore, dephosphorylation exhibited monotonic kinetics with a rate well below the diffusion limit. Thus, several different lines of analysis support the intermolecular model for dephosphorylation, in which the protein phosphatase must encounter its substrate to effect catalysis. In contrast to the monotonic kinetics of dephosphorylation, the phosphorylation reaction exhibited sigmoidal kinetics, with a rate that depended on membrane potential. Voltage dependence is an unlikely property for a kinetic step involving encounters resulting from diffusion. Furthermore, the velocity of the phosphorylation reaction exceeded the diffusion limit, and this observation is inconsistent with the intermolecular model. Thus, both intermolecular and intramolecular enzymatic mechanisms operate in the modulation of the calcium-activated potassium channel of the posterior pituitary. These studies provide a functional characterization of the interactions between enzyme and substrate in intact patches of cell membrane.
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Affiliation(s)
- K Bielefeldt
- Department of Physiology, University of Wisconsin Medical School, Madison 53706
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26
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Haack JA, Rosenberg RL. Calcium-dependent inactivation of L-type calcium channels in planar lipid bilayers. Biophys J 1994; 66:1051-60. [PMID: 8038377 PMCID: PMC1275812 DOI: 10.1016/s0006-3495(94)80886-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Intracellular Ca2+ can inhibit the activity of voltage-gated Ca channels by modulating the rate of channel inactivation. Ca(2+)-dependent inactivation of these channels may be a common negative feedback process important for regulating Ca2+ entry under physiological and pathological conditions. This article demonstrates that the inactivation of cardiac L-type Ca channels, reconstituted into planar lipid bilayers and studied in the presence of a dihydropyridine agonist, is sensitive to Ca2+. The rates and extents of inactivation, determined from ensemble averages of unitary Ba2+ currents, decreased when the calcium concentration facing the intracellular surface of the channel ([Ca2+]i) was lowered from approximately 10 microM to 20 nM by the addition of Ca2+ chelators. The rates and extents of Ba2+ current inactivation could also be increased by subsequent addition of Ca2+ raising the [Ca2+]i to 15 microM, thus demonstrating that the Ca2+ dependence of inactivation could be reversibly regulated by changes in [Ca2+]i. In addition, reconstituted Ca channels inactivated more quickly when the inward current was carried by Ca2+ than when it was carried by Ba2+, suggesting that local increases in [Ca2+]i could activate Ca(2+)-dependent inactivation. These data support models in which Ca2+ binds to the channel itself or to closely associated regulatory proteins to control the rate of channel inactivation, and are inconsistent with purely enzymatic models for channel inactivation.
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Affiliation(s)
- J A Haack
- Department of Pharmacology and Physiology, University of North Carolina at Chapel Hill 27599
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27
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Corcuff J, Guérineau N, Mariot P, Lussier B, Mollard P. Multiple cytosolic calcium signals and membrane electrical events evoked in single arginine vasopressin-stimulated corticotrophs. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41530-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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28
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Risso S, DeFelice LJ. Ca channel kinetics during the spontaneous heart beat in embryonic chick ventricle cells. Biophys J 1993; 65:1006-18. [PMID: 8241381 PMCID: PMC1225817 DOI: 10.1016/s0006-3495(93)81147-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The ability of Ca ions to inhibit Ca channels presents one of the most intriguing problems in membrane biophysics. Because of this negative feedback, Ca channels can regulate the current that flows through them. The kinetics of the channels depend on voltage, and, because the voltage controls the current, a strong interaction exists between voltage dependence and Ca dependence. In addition to this interaction, the proximity of pores and the local concentration of ions also determine how effectively the Ca ions influence channel kinetics. The present article proposes a model that incorporates voltage-dependent kinetics, current-dependent kinetics, and channel clustering. We have based the model on previous voltage-clamp data and on Ca and Ba action currents measured during the action potential in beating heart cells. In general we observe that great variability exists in channel kinetics from patch to patch: Ba or Ca currents have low or high amplitudes and slow or fast kinetics during essentially the same voltage regime, either applied step-protocols or spontaneous cell action potentials. To explain this variability, we have postulated that Ca channels interact through shared ions. The model we propose expands on our previous model for Ba currents. We use the same voltage-dependent rate constants for the Ca currents that we did for the Ba currents. However, we vary the current-dependent rate constants according to the species of the conducting ion. The model reproduces the main features of our data, and we use it to predict Ca channel kinetics under physiological conditions. Preliminary reports of this work have appeared (DeFelice et al., 1991, Biophys. J. 59:551a; Risso et al., 1992, Biophys. J. 61:248a).
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Affiliation(s)
- S Risso
- Department of Anatomy and Cell Biology, Emory University, Atlanta, Georgia 30322
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29
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Sihra TS, Nichols RA. Mechanisms in the regulation of neurotransmitter release from brain nerve terminals: current hypotheses. Neurochem Res 1993; 18:47-58. [PMID: 8096629 DOI: 10.1007/bf00966922] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- T S Sihra
- Department of Biochemistry, University of Dundee, Scotland
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30
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Armstrong DL, White RE. An enzymatic mechanism for potassium channel stimulation through pertussis-toxin-sensitive G proteins. Trends Neurosci 1992; 15:403-8. [PMID: 1279866 DOI: 10.1016/0166-2236(92)90192-b] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Many neurotransmitters inhibit secretion from electrically excitable cells by activating pertussis-toxin-sensitive G proteins that modulate voltage-gated ion channels. Recent electrophysiological studies of metabolically intact cells from mammalian and molluscan neuroendocrine systems have implicated protein phosphatases in this process. In this article David Armstrong and Richard White review these studies and suggest a biochemical pathway that might link one of the G proteins to protein phosphatase activity.
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Affiliation(s)
- D L Armstrong
- Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709
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31
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Nairn AC, Shenolikar S. The role of protein phosphatases in synaptic transmission, plasticity and neuronal development. Curr Opin Neurobiol 1992; 2:296-301. [PMID: 1322750 DOI: 10.1016/0959-4388(92)90118-5] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In the past year significant advances have been made in our understanding of the role of protein dephosphorylation in the control of neuronal function. Molecular cloning has identified a large number of serine/threonine and tyrosine protein phosphatases in the nervous system. Many of these enzymes are selectively enriched in the nervous system, some are localized to specific neurons, and yet others are expressed only during specific periods of neuronal development. The availability of purified protein phosphatases and selective inhibitors has facilitated the analysis of these enzymes and their role in the regulation of neurotransmitter receptors and ion channels.
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Affiliation(s)
- A C Nairn
- Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021
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