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Jiménez-Vargas JM, Possani LD, Luna-Ramírez K. Arthropod toxins acting on neuronal potassium channels. Neuropharmacology 2017; 127:139-160. [PMID: 28941737 DOI: 10.1016/j.neuropharm.2017.09.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 09/13/2017] [Accepted: 09/15/2017] [Indexed: 01/01/2023]
Abstract
Arthropod venoms are a rich mixture of biologically active compounds exerting different physiological actions across diverse phyla and affecting multiple organ systems including the central nervous system. Venom compounds can inhibit or activate ion channels, receptors and transporters with high specificity and affinity providing essential insights into ion channel function. In this review, we focus on arthropod toxins (scorpions, spiders, bees and centipedes) acting on neuronal potassium channels. A brief description of the K+ channels classification and structure is included and a compendium of neuronal K+ channels and the arthropod toxins that modify them have been listed. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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Affiliation(s)
- Juana María Jiménez-Vargas
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Lourival D Possani
- Departamento de Medicina Molecular y Bioprocesos, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad, 2001, Colonia Chamilpa, Apartado Postal 510-3, Cuernavaca 62210, Mexico
| | - Karen Luna-Ramírez
- Illawarra Health and Medical Research Institute, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia.
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Kawai Y, Yokoyama Y, Kaidoh M, Ohhashi T. Shear stress-induced ATP-mediated endothelial constitutive nitric oxide synthase expression in human lymphatic endothelial cells. Am J Physiol Cell Physiol 2010; 298:C647-55. [DOI: 10.1152/ajpcell.00249.2009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
To clarify the roles of lymphatic endothelial cells (LEC) in the regulation of endothelial constitutive nitric oxide synthase (ecNOS) expression, we examined the effects of shear stress on ecNOS immunohistochemical staining and mRNA and protein expression in human LEC as well as on ATP release from these cells. Shear stress at 0.5 or 1.0 dyn/cm2 increased ecNOS immunohistochemical staining and ecNOS mRNA and protein expression in cultured LEC. The same strength of shear stress produced a significant release of ATP from the LEC. Exogenous ATP ranging in concentration from 10−9 to 10−6 M produced a significant increase in ecNOS immunohistochemical expression in a dose-dependent manner. The increase in ecNOS expression mediated by 10−6M ATP was significantly reduced by 10−5 M suramin. Suramin (10−5 M) caused a significant reduction in the shear stress-mediated increases in ecNOS immunohistochemical staining and mRNA expression. The shear stress-mediated increases in ecNOS expression were significantly reduced by 3 mM tetraethylammonium, 10−4 M apamin, 10−9 M iberiotoxin, 10−5 M 2-aminoethoxydephenyl borate, or 10−5M xestospongin C, but not 10−5 M glybenclamide or 10−5 M nifedipine. The shear stress-mediated increases in ecNOS expression were significantly potentiated by pinacidil or NS1619 in a dose-dependent manner. The immunohistochemical expression of small- (SKCa) and big-conductance (BKCa) Ca2+-activated K+ channels was confirmed on the surfaces of human LEC. These findings suggest that shear stress produces a significant release of ATP from LEC, which activates the purinergic P2X/2Y receptor, thereby facilitating ecNOS mRNA and protein expression through inositol 1,4,5-trisphosphate-mediated release of intracellular Ca2+ ions and the activation of Ca2+-activated K+ channels in LEC.
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Affiliation(s)
- Yoshiko Kawai
- Department of Physiology, School of Medicine, Shinshu University, Matsumoto, Japan
| | - Yumiko Yokoyama
- Department of Physiology, School of Medicine, Shinshu University, Matsumoto, Japan
| | - Maki Kaidoh
- Department of Physiology, School of Medicine, Shinshu University, Matsumoto, Japan
| | - Toshio Ohhashi
- Department of Physiology, School of Medicine, Shinshu University, Matsumoto, Japan
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Favero M, Jiang DJ, Chiamulera C, Cangiano A, Fumagalli GF. Expression of small-conductance calcium-activated potassium channels (SK3) in skeletal muscle: regulation by muscle activity. J Physiol 2008; 586:4763-74. [PMID: 18703580 DOI: 10.1113/jphysiol.2008.156588] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The type 3 small conductance calcium-activated potassium channel (SK3) is expressed in embryonic and adult denervated skeletal muscles where it contributes to hyperexcitability. This study aimed at determining the role of muscle activity in regulating SK3 channels. Soleus muscles of adult rats were denervated by cutting the sciatic nerve. In reinnervation studies, the soleus nerve was crushed: in one group, muscles were reinnervated with electrically silent axons, by chronic sciatic nerve perfusion with tetrodotoxin. Several groups of denervated muscles were subjected to chronic direct electrical stimulation, using either fast (100 Hz) or slower patterns (20 or 30 Hz). The SK3 mRNA and protein levels in soleus muscle were determined by reverse transcriptional-PCR, Western blot and immunofluorescence. Both denervated and reinnervated-paralysed soleus muscles displayed similar up-regulation of SK3 mRNA and protein. Reinnervation with electrically active axons instead inhibited SK3 up-regulation. Chronic muscle direct stimulation in vivo, irrespective of the pattern used, reversed the denervation-induced up-regulation of SK3 expression or prevented it when initiated at the time of denervation. Chronic electrical stimulation of denervated muscles also completely prevented the development of the after-hyperpolarization (AHP) following the action potential, normally induced in the muscle fibres by denervation. We conclude that action potential activity evoked by motor neurones in muscle fibres is both necessary and sufficient to account for the physiological down-regulation of SK3 channels in the non-junctional membrane of skeletal muscle.
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Affiliation(s)
- Morgana Favero
- Department of Neurological and Visual Sciences, Section of Physiology, University of Verona, Strada Le Grazie 8, 37134 Verona, Italy
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Campos Rosa J, Galanakis D, Piergentili A, Bhandari K, Ganellin CR, Dunn PM, Jenkinson DH. Synthesis, molecular modeling, and pharmacological testing of bis-quinolinium cyclophanes: potent, non-peptidic blockers of the apamin-sensitive Ca(2+)-activated K(+) channel. J Med Chem 2000; 43:420-31. [PMID: 10669569 DOI: 10.1021/jm9902537] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis and pharmacological testing of two series of novel bis-quinolinium cyclophanes as blockers of the apamin-sensitive Ca(2+)-activated K(+) (SK(Ca)) channel are presented. In these cyclophanes the two 4-aminoquinolinium groups are joined at the ring N atoms (linker L) and at the exocyclic N atoms (linker A). In those cases where A and L contain two or more aromatic rings each, the activity of the compound is not critically dependent upon the nature of the linkers. When A and L each have only one benzene ring, the blocking potency changes dramatically with simple structural variations in the linkers. One of these smaller cyclophanes having A = benzene-1,4-diylbis(methylene) and L = benzene-1, 3-diylbis(methylene) (3j, 6,10-diaza-1,5(1,4)-diquinolina-3(1,3),8(1, 4)-dibenzenacyclodecaphanedium tritrifluoroacetate, UCL 1684) has an IC(50) of 3 nM and is the most potent non-peptidic SK(Ca) channel blocker described to date. Conformational analysis on the smaller cyclophanes using molecular modeling techniques suggests that the differences in the blocking potencies of the compounds may be attributable to their different conformational preferences.
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Affiliation(s)
- J Campos Rosa
- Department of Chemistry, University College London, Gower Street, London WC1E 6BT, U.K
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Schweitz H, Pacaud P, Diochot S, Moinier D, Lazdunski M. MIT(1), a black mamba toxin with a new and highly potent activity on intestinal contraction. FEBS Lett 1999; 461:183-8. [PMID: 10567694 DOI: 10.1016/s0014-5793(99)01459-3] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Mamba intestinal toxin (MIT(1)) isolated from Dendroaspis polylepis venom is a 81 amino acid polypeptide cross-linked by five disulphide bridges. MIT(1) has a very potent action on guinea-pig intestinal contractility. MIT(1) (1 nM) potently contracts longitudinal ileal muscle and distal colon, and this contraction is equivalent to that of 40 mM K(+). Conversely MIT(1) relaxes proximal colon again as potently as 40 mM K(+). The MIT(1)-induced effects are antagonised by tetrodotoxin (1 microM) in proximal and distal colon but not in longitudinal ileum. The MIT(1)-induced relaxation of the proximal colon is reversibly inhibited by the NO synthase inhibitor L-NAME (200 microM). (125)I-labelled MIT(1) binds with a very high affinity to both ileum and brain membranes (K(d)=1.3 pM and 0.9 pM, and B(max)=30 fmol/mg and 26 fmol/mg, respectively). MIT(1) is a very highly selective toxin for a receptor present both in the CNS and in the smooth muscle and which might be an as yet unidentified K(+) channel.
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Affiliation(s)
- H Schweitz
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UPR 411, 660, route des Lucioles, Sophia Antipolis, 06560, Valbonne, France
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Ishii TM, Maylie J, Adelman JP. Determinants of apamin and d-tubocurarine block in SK potassium channels. J Biol Chem 1997; 272:23195-200. [PMID: 9287325 DOI: 10.1074/jbc.272.37.23195] [Citation(s) in RCA: 220] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Small conductance calcium-activated potassium channels show a distinct pharmacology. Some, but not all, are blocked by the peptide toxin apamin, and apamin-sensitive channels are also blocked by d-tubocurarine. Cloned SK channels (small conductance calcium-activated potassium channel) recapitulate these properties. We have investigated the structural basis for these differences and found that two amino acid residues on either side of the deep pore are the primary determinants of sensitivity to apamin and differential block by d-tubocurarine. Therefore, the pharmacology of SK channels compared with other potassium channels correlates with structural differences in the outer pore region. However, introduction of a tyrosine residue in the position analogous to that which determines sensitivity to external tetraethylammonium for voltage-gated potassium channels endows SK channels with an equivalent tetraethylammonium sensitivity, indicating that the outer vestibules of the pores are similar. The pharmacology of channels formed in oocytes coinjected with SK1 and SK2 mRNAs, or with SK1-SK2 dimer mRNA, show that SK subunits may form heteromeric channels.
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Affiliation(s)
- T M Ishii
- Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA
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Campos Rosa J, Galanakis D, Ganellin CR, Dunn PM. Synthesis, molecular modeling, and K+ channel-blocking activity of dequalinium analogues having semirigid linkers. J Med Chem 1996; 39:4247-54. [PMID: 8863802 DOI: 10.1021/jm950884a] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Dequalinium [1,1'-(decane-1, 10-diyl)bis(2-methyl-4-aminoquinolinium)] is an effective blocker of the small conductance Ca2(+)-activated K+ channel. It has been shown that the number of methylene groups in the alkyl chain linking the two quinolinium rings of this type of molecule is not critical for activity. To further investigate the role of the linker, analogues of dequalinium have been synthesized, in which the alkyl chain has been replaced by CH2XCH2 where X is a rigid or semirigid group containing aromatic rings. The compounds have been tested for blockade of the slow after-hyperpolarization on rat sympathetic neurons. The most potent compounds have X = phenanthryl, fluorenyl, cis-stilbene, and C6H4(CH2)nC6H4, where n = 0-4. The conformational preferences of the compounds were investigated using the XED/COSMIC molecular modeling system. Although there is some dependence of the potency of the analogue on the conformational properties of the linker (X), overall, X groups having substantial structural differences are tolerated. It seems that X provides a support for the two quinolinium groups and does not interact with the channel directly. The intramolecular separation between the quinolinium rings, which is provided by rigid groups X, is not critical for activity; this may be attributed to the residual conformational mobility of the heterocycles and to the extensive delocalization of the positive charge. These two factors may permit favorable contacts between the quinolinium groups and the channel over a range of intramolecular separations.
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Affiliation(s)
- J Campos Rosa
- Department of Chemistry, University College London, U.K
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8
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Kwong PD, McDonald NQ, Sigler PB, Hendrickson WA. Structure of beta 2-bungarotoxin: potassium channel binding by Kunitz modules and targeted phospholipase action. Structure 1995; 3:1109-19. [PMID: 8590005 DOI: 10.1016/s0969-2126(01)00246-5] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND beta-bungarotoxin is a heterodimeric neurotoxin consisting of a phospholipase subunit linked by a disulfide bond to a K+ channel binding subunit which is a member of the Kunitz protease inhibitor superfamily. Toxicity, characterized by blockage of neural transmission, is achieved by the lipolytic action of the phospholipase targeted to the presynaptic membrane by the Kunitz module. RESULTS The crystal structure at 2.45 A resolution suggests that the ion channel binding region of the Kunitz subunit is at the opposite end of the module from the loop typically involved in protease binding. Analysis of the phospholipase subunit reveals a partially occluded substrate-binding surface and reduced hydrophobicity. CONCLUSIONS Molecular recognition by this Kunitz module appears to diverge considerably from more conventional superfamily members. The ion channel binding region identified here may mimic the regulatory interaction of endogenous neuropeptides. Adaptations of the phospholipase subunit make it uniquely suited to targeting and explain the remarkable ability of the toxin to avoid binding to non-target membranes. Insight into the mechanism of beta-bungarotoxin gained here may lead to the development of therapeutic strategies against not only pathological cells, but also enveloped viruses.
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Affiliation(s)
- P D Kwong
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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9
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Gmachl M, Kreil G. The precursors of the bee venom constituents apamin and MCD peptide are encoded by two genes in tandem which share the same 3'-exon. J Biol Chem 1995; 270:12704-8. [PMID: 7759523 DOI: 10.1074/jbc.270.21.12704] [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: 01/27/2023] Open
Abstract
From a cDNA library prepared from venom glands of worker bees, clones encoding the precursors of apamin and MCD peptide have been isolated. The cDNAs are similar at the 5'-ends and identical in their 3'-regions. Analysis of the corresponding genes has revealed the existence of six exons separated by introns rich in A + T. Starting from the 5'-end, these exons are arranged in the following order: three exons of the mast cell-degranulating (MCD) peptide precursor, two exons of the gene for the apamin precursor, and finally a 3'-exon present in both cDNAs. This suggests that the bulk of the apamin gene resides in the third intron of the MCD peptide gene. Using inverse polymerase chain reaction, a segment of genomic DNA upstream of the first exon of the MCD precursor gene was obtained. The sequence of this segment shows 81% identity to the DNA sequence preceding the first exon of the apamin gene and both contain a putative TATA box. We thus propose that the mRNA encoding the apamin precursor originates from a primary transcript which starts in the third intron of the MCD peptide gene. Both cDNAs encode unusually small precursors comprising only 46 amino acids in case of apamin and 50 in the case of the MCD peptide.
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Affiliation(s)
- M Gmachl
- Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg
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10
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Schweitz H, Vigne P, Moinier D, Frelin C, Lazdunski M. A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps). J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)49658-0] [Citation(s) in RCA: 235] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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11
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Zhukareva VA, Shatursky OYa, Lishko VK, Malysheva MK, Terletskaya YaT, Tsygankova OM, Grishin EV. Latrotoxin-like properties of a protein from brain. FEBS Lett 1992; 300:219-21. [PMID: 1555647 DOI: 10.1016/0014-5793(92)80849-c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In bovine brain cortex cytoplasm we have identified a soluble protein (L-protein) of M(r) approximately 90 kDa interacting with polyclonal antibodies to alpha-latrotoxin. The L-protein forms potential-dependent and cation-selective ion channels in BLM, which are blocked by Cd2+. The fusogenic activity of the L-protein was demonstrated on liposomes. We have arrived at the conclusion that the action mechanisms of the L-protein and alpha-latrotoxin are similar.
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Affiliation(s)
- V A Zhukareva
- Palladin Institute of Biochemistry, Ukrainian Academy of Sciences, Kiev, USSR
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12
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de Weille JR, Schweitz H, Maes P, Tartar A, Lazdunski M. Calciseptine, a peptide isolated from black mamba venom, is a specific blocker of the L-type calcium channel. Proc Natl Acad Sci U S A 1991; 88:2437-40. [PMID: 1848702 PMCID: PMC51247 DOI: 10.1073/pnas.88.6.2437] [Citation(s) in RCA: 157] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The venom of the black mamba contains a 60-amino acid peptide called calciseptine. The peptide has been fully sequenced. It is a smooth muscle relaxant and an inhibitor of cardiac contractions. Its physiological action resembles that of drugs, such as the 1,4-dihydropyridines, which are important in the treatment of cardiovascular diseases. Calciseptine, like the 1,4-dihydropyridines, selectively blocks L-type Ca2+ channels and is totally inactive on other voltage-dependent Ca2+ channels such as N-type and T-type channels. To our knowledge, it is the only natural polypeptide that has been shown to be a specific inhibitor of L-type Ca2+ channels.
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Affiliation(s)
- J R de Weille
- Institut de Pharmacologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique, Valbonne, France
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13
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Auguste P, Hugues M, Gravé B, Gesquière JC, Maes P, Tartar A, Romey G, Schweitz H, Lazdunski M. Leiurotoxin I (scyllatoxin), a peptide ligand for Ca2(+)-activated K+ channels. Chemical synthesis, radiolabeling, and receptor characterization. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39626-7] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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14
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15
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Dreyer F. Peptide Toxins and Potassium Channels. Rev Physiol Biochem Pharmacol 1990. [DOI: 10.1007/978-3-662-41884-0_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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16
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Triggle DJ, Langs DA, Janis RA. Ca2+ channel ligands: structure-function relationships of the 1,4-dihydropyridines. Med Res Rev 1989; 9:123-80. [PMID: 2654521 DOI: 10.1002/med.2610090203] [Citation(s) in RCA: 220] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- D J Triggle
- School of Pharmacy, State University of New York, Buffalo
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17
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Apamin: A highly selective and effective blocker of calcium-dependent potassium conductance. NEUROPHYSIOLOGY+ 1988. [DOI: 10.1007/bf02150264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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18
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Montero MC, Bolufer J, Ilundain A. Potassium transport in epithelial cells isolated from small intestine of the chicken. Pflugers Arch 1988; 412:422-6. [PMID: 3174400 DOI: 10.1007/bf01907562] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The transport of potassium has been studied in epithelial cells isolated from chicken small intestine using 86Rb as a tracer for K+. (i) The uptake studies revealed that about 60% of the total K+ net flux is inhibited by ouabain and therefore mediated by the Na+-K+-ATPase. About 20% of the ouabain-insensitive K+ net influx was inhibited by furosemide, bumetanide and by either Na+ or Cl- removal from the incubation solution, suggesting that a Na+/Cl-/K+ cotransport system might be present in chicken enterocytes. (ii) The efflux of K+ was measured from cells preloaded with 86Rb. K+ efflux was inhibited by Ba2+, quinine and verapamil; it was stimulated by A23187, and it was unaffected by 3,4-diaminopyridine. Apamin, that has no effect on basal rates of K+ efflux, abolished the effect of A23187. These findings suggest that K+ efflux appears to occur through Ca2+-activated K+ channels.
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Affiliation(s)
- M C Montero
- Departamento de Fisiología Animal, Faculdad de Farmacia, Sevilla, Spain
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19
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Hosey MM, Lazdunski M. Calcium channels: molecular pharmacology, structure and regulation. J Membr Biol 1988; 104:81-105. [PMID: 2903935 DOI: 10.1007/bf01870922] [Citation(s) in RCA: 299] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- M M Hosey
- Department of Biological Chemistry and Structure, Chicago Medical School, Illinois 60064
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20
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Triggle DJ. Endogenous Ligands for the Calcium Channel: Myths and Realities. THE CALCIUM CHANNEL: STRUCTURE, FUNCTION AND IMPLICATIONS 1988. [DOI: 10.1007/978-3-642-73914-9_44] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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21
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Montal M. Reconstitution of channel proteins from excitable cells in planar lipid bilayer membranes. J Membr Biol 1987; 98:101-15. [PMID: 2444708 DOI: 10.1007/bf01872123] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- M Montal
- Department of Neurosciences, Roche Institute of Molecular Biology, Nutley, New Jersey 07110
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22
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Blatz AL, Magleby KL. Single apamin-blocked Ca-activated K+ channels of small conductance in cultured rat skeletal muscle. Nature 1986; 323:718-20. [PMID: 2430185 DOI: 10.1038/323718a0] [Citation(s) in RCA: 392] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Action potentials in many excitable cells are followed by a prolonged afterhyperpolarization that modulates repetitive firing. Although it is established that the afterhyperpolarization is produced by Ca-activated K+ currents, the basis of these currents is not known. The large conductance (250 pS) Ca-activated K+ channel (BK channel) is not a major contributor to the afterhyperpolarization in non-innervated skeletal muscle and some nerve cells, because apamin, a neurotoxic component of bee venom, abolishes the afterhyperpolarization but does not block BK channels, and 5 mM extracellular tetraethylammonium ion (TEA) blocks BK channels but does not reduce the afterhyperpolarization. We now report single-channel currents from small conductance (10-14 pS) Ca-activated K+ channels (SK channels) with the necessary properties to account for the afterhyperpolarization. SK channels are blocked by apamin but not by 5 mM external TEA (TEAo). They are also highly Ca-sensitive at the negative membrane potentials associated with the afterhyperpolarization.
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23
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Burnham C, Braw R, Karlish SJ. A Ca-dependent K channel in "luminal" membranes from the renal outer medulla. J Membr Biol 1986; 93:177-86. [PMID: 2433451 DOI: 10.1007/bf01870809] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
This paper describes properties of 86Rb fluxes through K channels in "luminal" membrane vesicles prepared from rabbit renal outer medulla. By measuring 86Rb uptake against an opposing chemical gradient of K ions, using membranes loaded with KCl, a transient accumulation of isotope is observed, which is blocked by Ba ions. This is the behavior expected of a conductive Rb flux through a Ba-sensitive K channel. The 86Rb accumulation is driven by an electrical diffusion potential as shown in experiments using either vesicles loaded with different anions, or an outwardly directed Li gradient with a Li ionophore. The vesicles containing the channel show a cation selectivity with the order Rb greater than K greater than Cs greater than Li greater than Na greater than choline. The Ba-sensitive Rb flux is dependent on Ca within the vesicles, with a very high affinity estimated as K0.5 10 to 100 nM. The vesicles appear to be right-side-out. The Ba-sensitive 86Rb uptake is also inhibited by quinine K0.5 30 microM but is insensitive to tetraethyl ammonium ions and apamin. These isotope flux experiments complement electrophysiological experiments in providing independent evidence for the existence of K channels in the luminal surface of cells of this ascending limb of the loop of Henle. The very high Ca affinity suggests that cytoplasmic Ca could play an important role in regulation of transepithelial salt flux in this region of the nephron.
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24
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Schmid-Antomarchi H, Renaud JF, Romey G, Hugues M, Schmid A, Lazdunski M. The all-or-none role of innervation in expression of apamin receptor and of apamin-sensitive Ca2+-activated K+ channel in mammalian skeletal muscle. Proc Natl Acad Sci U S A 1985; 82:2188-91. [PMID: 2580309 PMCID: PMC397518 DOI: 10.1073/pnas.82.7.2188] [Citation(s) in RCA: 72] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The long-lasting after-hyperpolarization(s) (AHP) that follows the action potential in rat myotubes differentiated in culture is due to Ca2+-activated K+ channels. These channels have the property to be specifically blocked by the bee venom toxin apamin at low concentrations. Apamin has been used in this work to analyze, by electrophysiological and biochemical techniques, the role of innervation in expression of these important channels. The main results are as follows: (i) Long-lasting AHP that follows the action potential in rat myotubes in culture disappears when myotubes are cocultured with nerve cells from the spinal cord under the conditions of in vitro innervation. (ii) Extensor digitorum longus muscles from adult rats have action potentials that are not followed by AHP but AHP are systematically recorded after muscle denervation and they are blocked by apamin. (iii) Specific 125I-labeled apamin binding is undetectable in innervated muscle fibers but it becomes detectable 2-4 days after muscle denervation to be maximal 10 days after denervation. (iv) Apamin receptors detected with 125I-labeled apamin are present at fetal stages with biochemical characteristics identical to those found in myotubes in culture. The receptor number decreases as maturation proceeds and 125I-labeled apamin receptors completely disappear after the first week of postnatal life, in parallel with the disappearance of multi-innervation. All these results taken together strongly suggest an all-or-none effect of innervation on the expression of apamin-sensitive Ca2+-activated K+ channels.
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