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Abstract
Folding of transmembrane and secretory proteins occurs in the lumen of the endoplasmic reticulum (ER) before transportation to the cell surface and is monitored by the unfolded protein response (UPR) signaling pathway. The accumulation of unfolded proteins in the ER activates the UPR that restores ER homeostasis by regulating gene expression that leads to an increase in the protein-folding capacity of the ER and a decrease in the ER protein-folding load. However, prolonged UPR activity has been associated with cell death in multiple pathological conditions, including neurodegeneration. Here, we report a spontaneous recessive mouse mutation that causes progressive cerebellar granule cell death and peripheral motor axon degeneration. By positional cloning, we identify the mutation in this strain as a retrotransposon insertion in the Clcc1 gene, which encodes a putative chloride channel localized to the ER. Furthermore, we demonstrate that the C3H/HeSnJ inbred strain has late onset cerebellar degeneration due to this mutation. Interestingly, acute knockdown of Clcc1 expression in cultured cells increases sensitivity to ER stress. In agreement, GRP78, the major HSP70 family chaperone in the ER, is upregulated in Clcc1-deficient granule cells in vivo, and ubiquitinated proteins accumulate in these neurons before their degeneration. These data suggest that disruption of chloride homeostasis in the ER disrupts the protein-folding capacity of the ER, leading to eventual neuron death.
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2
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Sabirov RZ, Okada Y. The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity. J Physiol Sci 2009; 59:3-21. [PMID: 19340557 PMCID: PMC10717152 DOI: 10.1007/s12576-008-0008-4] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 11/05/2008] [Indexed: 10/20/2022]
Abstract
The maxi-anion channel is widely expressed and found in almost every part of the body. The channel is activated in response to osmotic cell swelling, to excision of the membrane patch, and also to some other physiologically and pathophysiologically relevant stimuli, such as salt stress in kidney macula densa as well as ischemia/hypoxia in heart and brain. Biophysically, the maxi-anion channel is characterized by a large single-channel conductance of 300-400 pS, which saturates at 580-640 pS with increasing the Cl(-) concentration. The channel discriminates well between Na(+) and Cl(-), but is poorly selective to other halides exhibiting weak electric-field selectivity with an Eisenman's selectivity sequence I. The maxi-anion channel has a wide pore with an effective radius of approximately 1.3 nm and permits passage not only of Cl(-) but also of some intracellular large organic anions, thereby releasing major extracellular signals and gliotransmitters such as glutamate(-) and ATP(4-). The channel-mediated efflux of these signaling molecules is associated with kidney tubuloglomerular feedback, cardiac ischemia/hypoxia, as well as brain ischemia/hypoxia and excitotoxic neurodegeneration. Despite the ubiquitous expression, well-defined properties and physiological/pathophysiological significance of this classical channel, the molecular entity has not been identified. Molecular identification of the maxi-anion channel is an urgent task that would greatly promote investigation in the fields not only of anion channel but also of physiological/pathophysiological signaling in the brain, heart and kidney.
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Affiliation(s)
- Ravshan Z. Sabirov
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
- Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, Tashkent, 100095 Uzbekistan
| | - Yasunobu Okada
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
- Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (Sokendai), Okazaki, 444-8585 Japan
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3
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Literature Alerts. J Microencapsul 2008. [DOI: 10.3109/02652048909019923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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4
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Sabirov RZ, Okada Y. ATP release via anion channels. Purinergic Signal 2005; 1:311-28. [PMID: 18404516 PMCID: PMC2096548 DOI: 10.1007/s11302-005-1557-0] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Revised: 07/19/2005] [Accepted: 07/26/2005] [Indexed: 11/30/2022] Open
Abstract
ATP serves not only as an energy source for all cell types but as an 'extracellular messenger' for autocrine and paracrine signalling. It is released from the cell via several different purinergic signal efflux pathways. ATP and its Mg(2+) and/or H(+) salts exist in anionic forms at physiological pH and may exit cells via some anion channel if the pore physically permits this. In this review we survey experimental data providing evidence for and against the release of ATP through anion channels. CFTR has long been considered a probable pathway for ATP release in airway epithelium and other types of cells expressing this protein, although non-CFTR ATP currents have also been observed. Volume-sensitive outwardly rectifying (VSOR) chloride channels are found in virtually all cell types and can physically accommodate or even permeate ATP(4-) in certain experimental conditions. However, pharmacological studies are controversial and argue against the actual involvement of the VSOR channel in significant release of ATP. A large-conductance anion channel whose open probability exhibits a bell-shaped voltage dependence is also ubiquitously expressed and represents a putative pathway for ATP release. This channel, called a maxi-anion channel, has a wide nanoscopic pore suitable for nucleotide transport and possesses an ATP-binding site in the middle of the pore lumen to facilitate the passage of the nucleotide. The maxi-anion channel conducts ATP and displays a pharmacological profile similar to that of ATP release in response to osmotic, ischemic, hypoxic and salt stresses. The relation of some other channels and transporters to the regulated release of ATP is also discussed.
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Affiliation(s)
- Ravshan Z. Sabirov
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
| | - Yasunobu Okada
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
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5
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Yoshimura H, Tada T, Iida H. Subcellular localization and oligomeric structure of the yeast putative stretch-activated Ca2+ channel component Mid1. Exp Cell Res 2004; 293:185-95. [PMID: 14729456 DOI: 10.1016/j.yexcr.2003.09.020] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The yeast Mid1 protein with an apparent molecular mass of 100 kDa is required for Ca2+ influx stimulated by the mating pheromone and by a capacitative calcium entrylike mechanism acting in response to Ca2+ depletion from the endoplasmic reticulum (ER) and functions as a stretch-activated Ca2+ -permeable channel when expressed in mammalian cells. Our previous work with protease protection experiments has indicated that Mid1 is present in the plasma membrane. In this study, we examined a possible intracellular localization of this protein by indirect fluorescence microscopy and found that Mid1 is present in the ER membrane as well as the plasma membrane. Intracellular fluorescence images for Mid1 were the same as those for the ER marker protein Sec71 but quite different from those of the Golgi protein Ypt1. The results were confirmed by membrane fractionation using Angiografin density gradient analysis. We also investigated the oligomeric structures and protein levels of Mid1 and found that Mid1 forms a 200-kDa oligomer by disulfide bonding. The protein level and modification of Mid1 in the plasma membrane and the ER membrane were unchanged by the mating pheromone. These findings provide new insight into the function of Mid1 in relation to localization, modification, and activation mechanisms.
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Affiliation(s)
- Hitoshi Yoshimura
- Department of Biology, Tokyo Gakugei University, 4-1-1 Nukui kita-machi, Koganei-shi, Tokyo 184-8501, Japan
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6
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Abstract
The Golgi complex is present in every eukaryotic cell and functions in posttranslational modifications and sorting of proteins and lipids to post-Golgi destinations. Both functions require an acidic lumenal pH and transport of substrates into and by-products out of the Golgi lumen. Endogenous ion channels are expected to be important for these features, but none has been described. Ion channels from an enriched Golgi fraction cleared of transiting proteins were incorporated into planar lipid bilayers. Eighty percent of the single-channel recordings revealed the same anion channel. This channel has novel properties and has been named GOLAC (Golgi anion channel). The channel has six subconductance states with a maximum conductance of 130 pS, is open over 95% of the time, and is not voltage-gated. Significant for Golgi function, the channel conductance is increased by reduction of pH on the lumenal surface. This channel may serve two nonexclusive functions: providing counterions for the acidification of the Golgi lumen by the H(+)-ATPase and removal of inorganic phosphate generated by glycosylation and sulfation of proteins and lipids in the Golgi.
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Affiliation(s)
- M H Nordeen
- Department of Cellular and Structural Biology, University of Colorado Health Sciences Center, Denver 80262, USA
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7
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Kourie JI. Chloride channels in the sarcoplasmic reticulum of muscle. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 68:263-300. [PMID: 9652173 DOI: 10.1016/s0079-6107(97)00029-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- J I Kourie
- Department of Chemistry, Australian National University, Canberra City, Australia
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8
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Szewczyk A. The intracellular potassium and chloride channels: properties, pharmacology and function (review). Mol Membr Biol 1998; 15:49-58. [PMID: 9724922 DOI: 10.3109/09687689809027518] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Channels selective for potassium or chloride ions are present in membranes of intracellular organelles such as sarcoplasmic (endoplasmic) reticulum, mitochondria, nucleus, synaptic vesicles, and chromaffin, and zymogen granules. They probably play an important role in cellular events such as compensation of electrical charges during transport of Ca2+, delta pH formation in mitochondria or V-ATPase containing membrane granules, and regulation of volume changes, due to potassium and chloride transport into intracellular organelles. Intracellular potassium and chloride channels could also be the target for pharmacologically active compounds. This mini-review describes the basic properties, pharmacology, and current hypotheses concerning the functional role of intracellular potassium and chloride channels.
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Affiliation(s)
- A Szewczyk
- Nencki Institute of Experimental Biology, Warsaw, Poland
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9
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Duncan RR, Westwood PK, Boyd A, Ashley RH. Rat brain p64H1, expression of a new member of the p64 chloride channel protein family in endoplasmic reticulum. J Biol Chem 1997; 272:23880-6. [PMID: 9295337 DOI: 10.1074/jbc.272.38.23880] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Many plasma membrane Cl- channels have been cloned, including the cystic fibrosis transmembrane conductance regulator and several members of the voltage-gated ClC family. In contrast, very little is known about the molecular identity of intracellular Cl- channels. We used a polymerase chain reaction-based approach to identify candidate genes in mammalian brain and cloned the cDNA corresponding to rat brain p64H1. This encoded a microsomal membrane protein of predicted Mr 28,635 homologous to the putative intracellular bovine kidney Cl- channel p64. In situ mRNA hybridization histochemistry showed marked expression in hippocampus and cerebellum, and in vitro expression revealed a large cytoplasmic domain, one membrane-spanning segment, and a small nonglycosylated N-terminal luminal domain. The predicted protein contained consensus phosphorylation sites for protein kinase C and protein kinase A, and protein kinase C-mediated phosphorylation increased the Mr of p64H1 to approximately 43,000, characteristic of the native protein in Western blots. Recombinant p64H1 was immunolocalized to the endoplasmic reticulum of human embryonic kidney 293 and HT-4 cells, and incorporation of human embryonic kidney 293 endoplasmic reticulum vesicles into planar lipid bilayers gave rise to intermediate conductance, outwardly rectifying anion channels. Although p64H1 is the first intracellular Cl- channel component or regulator to be identified in brain, Northern blotting revealed transcripts in many other rat tissues. This suggests that p64H1 may contribute widely to intracellular Cl- transport.
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Affiliation(s)
- R R Duncan
- Department of Biochemistry, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom
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10
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Clark AG, Murray D, Ashley RH. Single-channel properties of a rat brain endoplasmic reticulum anion channel. Biophys J 1997; 73:168-78. [PMID: 9199781 PMCID: PMC1180918 DOI: 10.1016/s0006-3495(97)78057-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Many intracellular membranes contain ion channels, although their physiological roles are often poorly understood. In this study we incorporated single anion channels colocalized with rat brain endoplasmic reticulum (ER) ryanodine-sensitive Ca(2+)-release channels into planar lipid bilayers. The channels opened in bursts, with more activity at negative (cytoplasm-ER lumen) membrane potentials, and they occupied four open conductance levels with frequencies well described by the binomial equation. The probability of a protomer being open decreased from approximately 0.7 at -40 mV to approximately 0.2 at +40 mV, and the channels selected between different anions in the order PSCN > PNO3 > PBr > PCl > PF. They were also permeant to cations, including the large cation Tris+ (PTris/PCl = 0.16). Their conductance saturated at 170 pS in choline Cl. The channels were inactivated by 15 microM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and blocked with low affinity (KD of 1-100 microM) by anthracene-9-carboxylic acid, ethacrynic acid, frusemide (furosemide), HEPES, the indanyloxyacetic acid derivative IAA-94, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), and Zn2+. Unlike protein translocation pores, the channels were unaffected by high salt concentrations or puromycin. They may regulate ER Ca2+ release, or be channel components en route to their final cellular destinations. Alternatively, they may contribute to the fusion machinery involved in intracellular membrane trafficking.
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Affiliation(s)
- A G Clark
- Department of Biochemistry, University of Edinburgh, Scotland, United Kingdom
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11
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Grosman C, Mariano MI, Bozzini JP, Reisin IL. Properties of two multisubstate Cl- channels from human syncytiotrophoblast reconstituted on planar lipid bilayers. J Membr Biol 1997; 157:83-95. [PMID: 9141361 DOI: 10.1007/s002329900218] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We describe the first successful reconstitution of placental ionic channels on planar lipid bilayers. An apical plasma membrane-enriched vesicle fraction from human syncytiotrophoblast at term was prepared by following isotonic agitation, differential centrifugation, and Mg2+-induced selective precipitation of nonapical membranes, and its purity was assessed by biochemical and morphological marker analysis. We have already reported that, unlike previous patch-clamp studies, nonselective cation channels were incorporated in most cases, a result consistent with the higher permeability for cations as compared with Cl- and with the low apical membrane potential difference at term revealed by fluorescent probe partition studies, and microelectrode techniques. In this paper, we report that Cl--selective channels were incorporated in 4% of successful reconstitutions (14 out of 353) and that their analysis revealed two types of activity. One of them was consistent with a voltage-dependent, 100-pS channel while the other was consistent with the lateral association of 47-pS conductive units, giving rise to multibarrelled, DIDS-sensitive channels of variable conductance (300 to 650 pS). The latter displayed a very complex behavior which included cooperative gating of conductive units, long-lived substates, voltage-dependent entry into an apparent inactivated state, and flickering activity. The role of the reported Cl- channels in transplacental ion transport and/or syncytium homeostasis remains to be determined.
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Affiliation(s)
- C Grosman
- Departamento de Química Analítica y Fisicoquímica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 (1113), Buenos Aires, Argentina
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12
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Kourie JI. ATP-sensitive voltage- and calcium-dependent chloride channels in sarcoplasmic reticulum vesicles from rabbit skeletal muscle. J Membr Biol 1997; 157:39-51. [PMID: 9141357 DOI: 10.1007/s002329900214] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Chloride channels in the sarcoplasmic reticulum (SR) are thought to play an essential role in excitation-contraction (E-C) coupling by balancing charge movement during calcium release and uptake. In this study the nucleotide-sensitivity of Cl- channels in the SR from rabbit skeletal muscle was investigated using the lipid bilayer technique. Two distinct ATP-sensitive Cl- channels that differ in their conductance and kinetic properties and in the mechanism of ATP-induced channel inhibition were observed. The first, a nonfrequent 150 pS channel was inhibited by trans (luminal) ATP, and the second, a common 75 pS small chloride (SCl) channel was inhibited by cis (cytoplasmic) ATP. In the case of the SCl channel the ATP-induced reversible decline in the values of current (maximal current amplitude, Imax and integral current, I') and kinetic parameters (frequency of opening FO, probability of the channel being open PO, mean open TO and closed Tc times) show a nonspecific block of the voltage- and Ca2+-dependent SCl channel. ATP was a more potent blocker from the cytoplasmic side than from the luminal side of the channel. The SCl channel block was not due to Ca2+ chelation by ATP, nor to phosphorylation of the channel protein. The inhibitory action of ATP was mimicked by the nonhydrolyzable analogue adenylylimidodiphosphate (AMP-PNP) in the absence of Mg2+. The inhibitory potency of the adenine nucleotides was charge dependent in the following order ATP4- > ADP3- > > > AMP2-. The data suggest that ATP-induced effects are mediated via an open channel block mechanism. Modulation of the SCl channel by [ATP]cis and [Ca2+]cis indicates that (i) this channel senses the bioenergetic state of the muscle fiber and (ii) it is linked to the ATP-dependent cycling of the Ca2+ between the SR and the sarcoplasm.
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Affiliation(s)
- J I Kourie
- Muscle Research Group, Division of Neuroscience, John Curtin School of Medical Research, ANU, PO Box 334, Canberra City, ACT, 2601 Australia
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13
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Huang SG, Klingenberg M. Chloride channel properties of the uncoupling protein from brown adipose tissue mitochondria: a patch-clamp study. Biochemistry 1996; 35:16806-14. [PMID: 8988019 DOI: 10.1021/bi960989v] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The uncoupling protein (UCP) from brown adipose tissue mitochondria possesses H+ and Cl- transport activities [reviewed in Klingenberg, M. (1990) Trends Biochem. Sci. 15, 108-112]. Being a member of a mitochondrial carrier family, the transport of H+ and Cl- is carrier-like, i.e., much slower as compared to channels. Here we report that UCP reconstituted into giant liposomes displays stable chloride channel properties under patch-clamp conditions. The transport inhibitors (GTP, GDP, ATP, and ADP) also inhibit this channel in a reversible way, showing that the channel activity is associated with UCP. The slightly inward-rectifying chloride channel has a unit conductance of approximately 75 pS in symmetrical 100 mM KCl and closes at high positive potentials on the matrix side of UCP. Channel gatings switch from slow open-closure transitions to fast flickerings as the holding potential increases over +60 mV. Substitution experiments reveal a strong discrimination against cations [P(Cl-)/P(K+) approximately 17] and a permeability ratio order of Cl- > Br- > F- > SCN- > I- > NO3- > SO4(2-) > HPO4(2-) > gluconate. Nucleotide inhibition studies indicate that 70% UCP molecules had its matrix side oriented outside in the giant liposomes. Fatty acids, pH, divalent cations (Ca2+ and Mg2+), and mersalyl do not influence these Cl- currents. The Cl- channel can be blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) from the matrix side of UCP. The data are consistent with a dimer consisting of two monomeric 75-pS Cl- channels or with a monomeric 150-pS channel having a 50% subconductance state. The channel current increases with Cl- concentration showing a typical saturation curve with Km approximately 63 mM and gmax approximately 120 pS (100 mM KCl in the pipet). The Cl- conductance measured under these conditions is 6 orders of magnitude higher than the Cl- transport activity reported earlier, suggesting that the UCP has the potential of behaving as an anion channel.
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Affiliation(s)
- S G Huang
- Institute of Physical Biochemistry, University of Munich, Germany.
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14
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Howell S, Duncan RR, Ashley RH. Identification and characterisation of a homologue of p64 in rat tissues. FEBS Lett 1996; 390:207-10. [PMID: 8706861 DOI: 10.1016/0014-5793(96)00676-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Previous work has suggested that the gene encoding p64, a component of a bovine kidney intracellular chloride channel, may be a member of a gene family. We have raised a polyclonal antibody to an E. coli fusion protein which has sequence similarity to p64. Immunoblotting detected a protein in rat brain, kidney, liver and lung. In rat brain, the protein was enriched in cerebellar microsomal membranes. Western blot analyses of denaturing and blue native polyacrylamide gels indicated that the protein is a single non-disulphide-linked polypeptide chain with an apparent M(r) of 43 kDa that contributes to a native protein complex with an apparent M(r) of 130 kDa.
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Affiliation(s)
- S Howell
- Department of Biochemistry, University of Edinburgh, UK
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15
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Kourie JI, Laver DR, Junankar PR, Gage PW, Dulhunty AF. Characteristics of two types of chloride channel in sarcoplasmic reticulum vesicles from rabbit skeletal muscle. Biophys J 1996; 70:202-21. [PMID: 8770199 PMCID: PMC1224921 DOI: 10.1016/s0006-3495(96)79564-4] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A comparison is made of two types of chloride-selective channel in skeletal muscle sarcoplasmic reticulum (SR) vesicles incorporated into lipid bilayers. The I/V relationships of both channels, in 250/50 mM Cl- (cis/trans), were linear between -20 and +60 mV (cis potential,) reversed near Ecl and had slope conductances of approximately 250 pS for the big chloride (BCl) channel and approximately 70 pS for the novel, small chloride (SCl) channel. The protein composition of vesicles indicated that both channels originated from longitudinal SR and terminal cisternae. BCl and SCl channels responded differently to cis SO4(2-) (30-70 mM), 4,4'-diisothiocyanatostilbene 2,2'-disulfonic acid (8-80 microM) and to bilayer potential. The BCl channel open probability was high at all potentials, whereas SCl channels exhibited time-dependent activation and inactivation at negative potentials and deactivation at positive potentials. The duration and frequency of SCl channel openings were minimal at positive potentials and maximal at -40 mV, and were stationary during periods of activity. A substate analysis was performed using the Hidden Markov Model (S. H. Chung, J. B. Moore, L. Xia, L. S. Premkumar, and P. W. Gage, 1990, Phil. Trans. R. Soc. Lond. B., 329:265-285) and the algorithm EVPROC (evaluated here). SCl channels exhibited transitions between 5 and 7 conductance levels. BCl channels had 7-13 predominant levels plus many more short-lived substates. SCl channels have not been described in previous reports of Cl- channels in skeletal muscle SR.
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Affiliation(s)
- J I Kourie
- John Curtin School of Medical Research, Australian National University, Canberra City, Australia.
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16
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Abstract
Chloride channels are present in a variety of intracellular organelles (Golgi, endosomes, endoplasmic reticulum, and sarcoplasmic reticulum) where they serve largely to shunt the membrane potential created by other ion-translocating processes. Electrophysiological studies have shown that the Cl- channels of the endoplasmic and sarcoplasmic reticula facilitate the efflux of Ca2+. In the Golgi and some endosomes, the open Cl- channels (probably the cystic fibrosis transmembrane conductance regulator) favor accumulation of H+.
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Affiliation(s)
- Q al-Awqati
- College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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17
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Oberleithner H, Brinckmann E, Schwab A, Krohne G. Imaging nuclear pores of aldosterone-sensitive kidney cells by atomic force microscopy. Proc Natl Acad Sci U S A 1994; 91:9784-8. [PMID: 7937891 PMCID: PMC44901 DOI: 10.1073/pnas.91.21.9784] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
In nuclei of renal target cells, aldosterone enhances transcriptional activity followed by the translocation of specific RNA molecules across the nuclear envelope. Trafficking between cell nucleus and cytoplasm occurs via nuclear pore complexes (NPCs) located in the double-layered nuclear envelope. We investigated the nucleocytoplasmic transport route by structure-function analysis at subcellular level in quiescent and aldosterone-stimulated cells. With atomic-force microscopy (AFM) we imaged individual pores of the nuclear surface of cultured kidney cells and related the number of pores per micron2 to nuclear envelope conductance (Gn, per micron2) evaluated electrically by current injection into the isolated nucleus. NPCs were equally distributed resembling "donut-like" structures with outer diameters of 134 +/- 12 nm (n = 50), each equipped with a central channel. Six hours of aldosterone exposure (0.1 microM) increased the number of NPCs per micron 2 of nuclear surface from 7.4 +/- 0.4 to 9.8 +/- 0.4 (n = 12; P < 0.01). At the same time Gn rose from 6900 +/- 520 to 9600 +/- 610 pS/micron2 paralleled by an increase of the intranuclear electrical potential from -2.8 +/- 0.2 to -6.2 +/- 0.4 mV (n = 18; P < 0.01). Assuming that NPCs represent the sole conductive pathway in the nuclear envelope, we calculate a mean single NPC conductance of 932 and 980 pS, in the absence and presence of aldosterone, respectively. We conclude that aldosterone facilitates nucleocytoplasmic transport by increasing the number of NPCs but not by modifying their biophysical properties. Possibly, aldosterone controls similar transport mechanisms in both plasma membrane and nuclear envelope.
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Affiliation(s)
- H Oberleithner
- Department of Physiology, University of Würzburg, Germany
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18
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DeBin JA, Wood MR, Pfenninger KH, Strichartz GR. A chloride channel reconstituted from fetal rat brain growth cones. J Membr Biol 1994; 141:7-19. [PMID: 7966248 DOI: 10.1007/bf00232869] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Chloride channels were reconstituted into planar lipid bilayers isolated from a preparation of growth cone particles (GCPs) isolated from fetal rat brain. One type of channel was predominantly seen and some of its biophysical and pharmacological properties were studied. The single channel i-V relationship was curvilinear with a chord conductance of 75 pS at +30 mV in symmetric 200 mM NaCl solutions buffered with phosphate. The channel was inactivated by depolarization, and this inactivation was reversed rapidly upon returning to -25 mV. The Cl- channel was significantly permeant to Na+ ions (PNa/PCl = 0.26), and the relative halide permeabilities were determined to be: I(1.92) > Br(1.73) > Cl(1.0) > F(0.34). The channel was inhibited by the common stilbene compounds (DIDS, SITS, DNDS), as well as by Zn2+ ions and an indanyloxyacetic acid derivative. A developmental role for the GCP Cl- channel is suggested by the observation that adult rat brain synaptosomal membranes were nearly devoid of this type of Cl- channel.
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Affiliation(s)
- J A DeBin
- Anesthesia Research Laboratories, Brigham and Women's Hospital, Boston, Massachusetts 02115
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19
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Bégault B, Anagnostopoulos T, Edelman A. ATP-regulated chloride conductance in endoplasmic reticulum (ER)-enriched pig pancreas microsomes. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1152:319-27. [PMID: 8218333 DOI: 10.1016/0005-2736(93)90264-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The Cl- conductance of endoplasmic reticulum-enriched pancreatic microsomes was identified. Its regulation by nucleotides was investigated by measuring the rate of cation ionophore-induced microsome swelling in the presence of an inward Cl- gradient. The conductance was solubilized and reconstituted into liposomes. The Cl- conductance in intact microsomes was inhibited by stilbene (10(-4) M) and indanyloxyacetic acid (10(-5) M) derivatives. ATP increased Cl- conductance with half-maximal stimulation at 8 x 10(-6) M. Other trinucleotides (GTP, CTP and UTP) were without effect at 10(-4) M. The non-hydrolysable analogue of ATP, adenosine 5'-[beta gamma-methylene]triphosphate (AppCH2p) increased Cl- conductance with a potency similar to that of ATP. The same concentration of adenosine 5'-[gamma-thio]triphosphate (ATP gamma S) which is a substrate for kinases, had no effect. ATP stimulation of Cl- conductance was inhibited by stilbene derivatives. The data suggest the presence of at least one ATP-binding site, and show that the ATP does not need to be hydrolyzed and that its spatial conformation is important for activating the Cl- conductance. Solubilized microsomal proteins reconstituted into liposomes retained their stilbene-inhibited, ATP-stimulated Cl- conductance. A 167 kDa protein was detected by anti-CFTR antibodies in the intact microsomes, but not in the solubilized proteins. The 64 kDa protein (a component of a ubiquitous Cl- channel) was detected in the both intact and solubilized microsomes. These results suggest that this Cl- conductance is not a CFTR protein.
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Affiliation(s)
- B Bégault
- INSERUM U.323 CHU Necker, Paris, France
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20
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Völkl H, Friedrich F, Häussinger D, Lang F. Effect of cell volume on Acridine Orange fluorescence in hepatocytes. Biochem J 1993; 295 ( Pt 1):11-4. [PMID: 8216204 PMCID: PMC1134812 DOI: 10.1042/bj2950011] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Hepatic proteolysis is inhibited by cell swelling following a variety of experimental manoeuvres, such as reduction of extracellular osmolarity, concentrative uptake of amino acids, or blockade of K+ channels by barium. On the other hand, proteolysis is known to be accomplished by pH-sensitive lysosomal proteases. Accordingly, NH3/NH4+ inhibits proteolysis by intralysosomal alkalinization. The present study has been performed to test for an effect of cell volume on the pH of acidic intracellular compartments, as assessed by Acridine Orange fluorescence at > 520 nm (F > 520). F > 520 is enhanced by NH3/NH4+ (2 and 20 mmol/l respectively), by glutamine (2 mmol/l), by the K(+)-channel blocker barium (10 mmol/l) and by reduction of extracellular osmolarity (by 20 and 80 mosmol/l respectively). The observations point to release of Acridine Orange from acidic cellular compartments, which is indicative of alkalinization of these compartments during cell swelling. This effect may contribute to the regulation of proteolysis.
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Affiliation(s)
- H Völkl
- Institute of Physiology, University of Innsbruck, Austria
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21
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Mathiasen D, Røssum LM, Robinson IM, Burgoyne RD, East JM, Møller M, Rasmussen HN, Treiman M. Isolation of chromaffin cell thapsigargin-sensitive Ca2+ store in light microsomes from bovine adrenal medulla. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1993; 25:641-52. [PMID: 8349007 DOI: 10.1016/0020-711x(93)90348-i] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
1. A subcellular fractionation procedure for bovine adrenal glands was designed with the aim to study the biochemical properties of Ca2+ stores in chromaffin cells. 2. The thapsigargin-sensitive compartment of Ca2+ stores was found to be highly enriched in a light microsomal fraction (LMF) on a 15-30% linear sucrose gradient, and was found to be essentially devoid of contamination by plasma, mitochondrial or secretory granule membranes. 3. A Ca(2+)-pumping ATPase was identified in this LMF as a 97 kDa protein forming an acid-stable, Ca(2+)-dependent, thapsigargin-sensitive phosphorylated intermediate upon incubation with [gamma-32P]ATP, suggesting this protein to represent a SERCA-3 isoform of Ca2+ ATPases. 4. A major 162 kDa protein, previously demonstrated in the isolated chromaffin cells, was enriched in the LMF, distributing on sucrose gradients in parallel with the thapsigargin-sensitive Ca2+ uptake. 5. LMF appears to represent a part of the thapsigargin-sensitive Ca2+ store of chromaffin cells, and should be useful for further studies of the store properties at the subcellular and molecular level.
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Affiliation(s)
- D Mathiasen
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
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22
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Oberleithner H, Schuricht B, Wünsch S, Schneider S, Püschel B. Role of H+ ions in volume and voltage of epithelial cell nuclei. Pflugers Arch 1993; 423:88-96. [PMID: 8387671 DOI: 10.1007/bf00374965] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Condensation of chromatin depends upon the ion composition in the cell nucleus. We tested in isolated nuclei of Madin-Darby canine kidney cells the influence of various ions on nuclear volume (i. e. DNA packing) and intranuclear voltage. After isolation, nuclei were superfused with cytosolic solutions in which Na+, K+, Ca2+ and H+ ions were varied. With video-imaging and microelectrode techniques nuclear volume and intranuclear potential were measured in response to the various ions. In control cytosolic solution, isolated nuclei exhibited an intranuclear electrical potential of -6.5 +/- 0.5 mV (relative to a reference electrode in the cytosolic solution) corresponding to a nuclear volume of 250 +/- 10 fl (n = 104). Changing the Na+, K+ or free Ca2+ concentration in the superfusate in the physiological range resulted in minor changes of volume and intranuclear potential whereas pH altered both parameters dramatically. Nuclear swelling and intranuclear negative voltage increased with alkalinization and decreased when pH was reduced. An intact nuclear envelope was found to be no prerequisite for maintaining intranuclear negativity, indicating that the composition and functional state of nuclear chromatin rather than specific ion permeabilities of the nuclear envelope determine nuclear electrical potential. We present a model that explains nuclear volume and voltage on the basis of interaction between negatively charged DNA and positively charged histones of the nuclear chromatin.
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Affiliation(s)
- H Oberleithner
- Department of Physiology, University of Würzburg, Germany
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23
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Varga S, Martonosi A. Giant sarcoplasmic reticulum vesicles: a study of membrane morphogenesis. J Muscle Res Cell Motil 1992; 13:497-510. [PMID: 1281163 DOI: 10.1007/bf01737992] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Rabbit sarcoplasmic reticulum vesicles were fused into giant proteoliposomes in a medium of 0.1 M KCl, 10 mM Tris-maleate, pH 7.0, 10 micrograms ml-1 antipain, 10 micrograms ml-1 leupeptin, 25 IU per ml Trasylol, 3 mM NaN3, 3.75% PEG 1500 and 3% DMSO by brief exposure to 37 degrees C, followed by incubation for 4 h at 25 degrees C. Approximately 5-10% of the sarcoplasmic reticulum elements underwent fusion, forming single-walled spherical vesicles of 1-25 microns diameter, in which the polarity of the native membrane was preserved. The Ca(2+)-stimulated ATPase activity remained essentially unchanged after fusion. On exposure to decavanadate in a Ca(2+)-free medium the spherical vesicles assumed a corrugated appearance with the formation of long ridges separated by deep furrows that eventually pinched off longitudinally and separated into numerous long crystalline tubules of uniform (approximately 0.1 microns) diameter. The vanadate-induced transformation of giant vesicles into tubules implies that the geometry of the sarcoplasmic reticulum membrane is determined by the conformation of the Ca(2+)-ATPase.
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Affiliation(s)
- S Varga
- Department of Biochemistry and Molecular Biology, State University of New York, Syracuse 13210
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24
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Nomura K, Sokabe M. Anion channels from rat brain synaptosomal membranes incorporated into planar bilayers. J Membr Biol 1991; 124:53-62. [PMID: 1722514 DOI: 10.1007/bf01871364] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Synaptic membranes from rat brain were incorporated into planar lipid bilayers, and the characteristics of two types of anion-selective channels (type I and type II) were investigated. In asymmetric BaCl2 buffers (cis, 100 mM/trans, 25 mM), single channel conductances at -40 mV were 70 pS (type I) and 120 pS (type II). Permeability ratios (PNa:PBa:PCl) calculated from the Goldman-Hodgkin-Katz current equation for type I and type II channels were 0.23:0.04:1 and 0.05:0.03:1, respectively. Both channels exhibited characteristic voltage-dependent bursting activities. Open probability for type I channels had a maximum of approximately 0.7 at about 0 mV and decreased to zero at greater transmembrane potentials of either polarity. Type II channels were relatively voltage independent at negative voltages and were inactivated at highly positive voltages. Type I channels showed spontaneous irreversible inactivation often preceded by sudden transition to subconducting states. DIDS blocked type I channels only from the cis side, while it blocked type II channels from either side.
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Affiliation(s)
- K Nomura
- Department of Pediatrics, Nagoya University School of Medicine, Japan
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25
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Hirashima N, Ishibashi H, Kirino Y. Comparative electrophysiological study of reconstituted giant vesicle preparations of the rabbit skeletal muscle sarcoplasmic reticulum K+ channel. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1067:235-40. [PMID: 1878374 DOI: 10.1016/0005-2736(91)90049-e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Sarcoplasmic reticulum (SR) membranes isolated from rabbit skeletal muscle were reconstituted into two types of giant vesicles: (1) Giant proteoliposomes prepared by freeze-thawing of a mixture of SR vesicles and sonicated phospholipid vesicles without the use of detergent. (2) Giant SR vesicles prepared by fusion of SR vesicles using poly(ethylene glycol) (PEG) as a fusogen and without the addition of exogenous lipid. These giant vesicles were patch-clamped and properties of the single voltage-dependent potassium channel in the excised patch were studied. Single-channel conductance in a symmetrical solution of 0.1 M KCl and 1 mM CaCl2 was 140.0 +/- 10 pS (n = 5) for freeze-thawed vesicles and 136.4 +/- 15 pS (n = 7) for PEG vesicles. Both types of vesicles exhibited a sub-conductance state having 55% of the fully open state conductance. The voltage-dependence of open-channel probability could be expressed in terms of thermodynamic parameters of delta Gi = 0.95 kcal/mol and z = -0.77 for freeze-thawed vesicles and delta Gi = 0.92 kcal/mol and z = -0.87 for PEG vesicles. These values correlated well with previous data obtained by fusion of native SR vesicles with a planar lipid membrane. Channel orientation was found to be conserved in both types of vesicles used in the present study.
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Affiliation(s)
- N Hirashima
- Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan
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26
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Wunder UR, Colombini M. Patch clamping VDAC in liposomes containing whole mitochondrial membranes. J Membr Biol 1991; 123:83-91. [PMID: 1723104 DOI: 10.1007/bf01993966] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Whole mitochondrial membranes isolated from Neurospora crassa were reconstituted into liposomes and patch clamped. Clear activity characteristic of the mitochondrial channel VDAC was found, namely: open state conductance of 650 pS (in 150 mM KCl, 1 mM CaCl2, 20 mM HEPES, pH 7.2), voltage-dependent closure at both positive and negative potentials, change in conductance upon channel closure of about 450 pS in response to negative and positive potentials, and increased voltage dependence in the presence of König's polyanion. This is the first clear demonstration of VDAC single channels using the patch-clamp technique, even though others used this method before to study whole mitochondrial membranes and liposomes containing mitochondrial proteins. We also found one other channel with a conductance change of about 120 pS.
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Affiliation(s)
- U R Wunder
- Department of Zoology, University of Maryland, College Park 20742
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27
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Abstract
Chloride-selective ion channels were measured from isolated rat liver nuclei. Single ion channel currents were recorded in both "nuclear-attached" and in excised patches in the inside-out configuration of the patch-clamp technique. Two types of chloride conductance were defined, a large conductance (150 pS; iCl,N) channel with complex kinetics and multiple substates, and a second smaller conductance (58 pS;ICln) channel sensitive to block by ATP. The channels were inhibited by pharmacological agents known to block chloride channels and were insensitive to internal and external changes in calcium and magnesium. Presumably the channels reside in the external membrane of the nuclear double membrane and may mediate charge balance in the release and uptake of calcium from the perinuclear space.
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Affiliation(s)
- L Tabares
- Department of Pharmacology, Mayo Foundation, Rochester, Minnesota 55905
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28
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Dehlinger-Kremer M, Zeuzem S, Schulz I. Interaction of caffeine-, IP3- and vanadate-sensitive Ca2+ pools in acinar cells of the exocrine pancreas. J Membr Biol 1991; 119:85-100. [PMID: 2008014 DOI: 10.1007/bf01868543] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Previous studies have shown the existence of functionally distinguishable inositol 1,4,5-trisphosphate- (IP3) sensitive and IP3-insensitive nonmitochondrial intracellular Ca2+ pools in acinar cells of the exocrine pancreas. For further characterization of Ca2+ pools, endoplasmic reticulum (ER) membrane vesicles were separated by Percoll gradient centrifugation which allowed us to distinguish five discrete fractions designated P1 to P5 from the top to the bottom of the gradient. Measuring Ca2+ uptake and Ca2+ release with a Ca2+ electrode, we could differentiate three nonmitochondrial intracellular Ca2+ pools: (i) an IP3-sensitive Ca2+ pool (IsCaP), vanadate- and caffeine-insensitive, (ii) a caffeine-sensitive Ca2+ pool (CasCaP), vanadate- and IP3-insensitive, and (iii) a vanadate-sensitive Ca2+ pool (VasCaP), neither IP3- nor caffeine-sensitive, into which Ca2+ uptake is mediated via a Ca2+ ATPase sensitive to vanadate at 10(-4) mol/liter. A fourth Ca2+ pool is neither IP3- nor caffeine- or vanadate-sensitive. Percoll fraction P1 contained essentially the IsCaP, CasCaP and VasCaP and was mainly used for studies on Ca2+ uptake and Ca2+ release. When membrane vesicles were incubated in the presence of caffeine (2 x 10(-2) mol/liter), Ca2+ uptake up to the steady state [Ca2+] did not appear to be altered as compared to the control Ca2+ uptake. However, in control vesicles spontaneous Ca2+ release occurred after the steady state had been reached, whereas caffeine-pretreated vesicles did not spontaneously release Ca2+. Addition of IP3 at steady state [Ca2+] induced similar Ca2+ release followed by Ca2+ reuptake in both caffeine-pretreated and control vesicles. However, when caffeine was acutely added at steady state, Ca2+ was released from all Ca2+ pools including the IsCaP. Following Ca2+ reuptake after IP3 had been added, a second addition of IP3 to control vesicles induced further but smaller Ca2+ release, and a third addition resulted in a steady Ca2+ efflux by which all Ca2+ that had been taken up was released. This steady Ca2+ release started at a Ca2+ concentration between 5.5-8 x 10(-7) mol/liter and could also be induced by the IP3 analogue inositol 1,4,5-trisphosphorothioate (IPS3) or by addition of Ca2+ itself. Ruthenium red (10(-5) mol/liter) inhibited both caffeine-induced as well as Ca2(+)-induced but not IP3-induced Ca2+ release. Heparin (100 micrograms/ml) inhibited IP3- but not caffeine-induced Ca2+ release. The data indicate the presence of at least three separate Ca2+ pools in pancreatic acinar cells: the IsCaP, CasCaP and VasCaP. During Ca2+ uptake these Ca2+ pools appear to be separate.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M Dehlinger-Kremer
- Max-Planck-Institut für Biophysik, Frankfurt am Main, Federal Republic of Germany
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29
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Petersen OH, Wakui M. Oscillating intracellular Ca2+ signals evoked by activation of receptors linked to inositol lipid hydrolysis: mechanism of generation. J Membr Biol 1990; 118:93-105. [PMID: 2176239 DOI: 10.1007/bf01868467] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- O H Petersen
- M.R.C. Secretory Control Research Group, Department of Physiology, University of Liverpool, United Kingdom
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30
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Schmid A, Dehlinger-Kremer M, Schulz I, Gögelein H. Voltage-dependent InsP3-insensitive calcium channels in membranes of pancreatic endoplasmic reticulum vesicles. Nature 1990; 346:374-6. [PMID: 1695718 DOI: 10.1038/346374a0] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Stimulus-secretion coupling in exocrine glands involves Ca2+ release from intracellular stores. In endoplasmic reticulum vesicle preparations from rat exocrine pancreas, an inositol 1,4,5-trisphosphate(InsP3)-sensitive, as well as an InsP3-insensitive, Ca2+ pool has been characterized. But Ca2+ channels in the endoplasmic reticulum of rat exocrine pancreas have not been demonstrated at the level of single-channel current. We have now used the patch-clamp technique on endoplasmic reticulum vesicles fused by means of the dehydration-rehydration method. In excised patches, single Ba2(+)- and Ca2(+)-selective channels were recorded. The channel activity was markedly voltage-dependent. Caffeine increased channel open-state probability, whereas ruthenium red and Cd2+ blocked single-channel currents. Ryanodine, nifedipine and heparin had no effect on channel activity. The channel activity was not dependent on the free Ca2+ concentration, the presence of InsP3, or pH. We conclude that this calcium channel mediates Ca2+ release from an intracellular store through an InsP3-insensitive mechanism.
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Affiliation(s)
- A Schmid
- Max-Planck-Institut für Biophysik, Frankfurt (Main), FRG
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31
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Abstract
Ionic channels in a human monocyte cell line (U937) were studied with the inside-out patch-clamp technique. A Ca2(+)-activated K+ channel and three Cl- -selective channels were observed. The Ca2(+)-activated K+ channel had an inward-rectifying current-voltage relationship with slope conductance of 28 pS, and was not dependent on membrane potential. Among the three Cl- channels, an outward-rectifying 28-pS channel was most frequently observed. The permeability ratio (Cl-/Na+) was 4-5 and CH3SO4- was also permeant. The channel became less active with increasing polarizations in either direction, and was inactive beyond +/- 120 mV. The channel, observed as bursts, occasionally had rapid events within the bursts, suggesting the presence of another mode of kinetics. Diisothiocyanatostilbene-disulfonic acid (DIDS) blocked the channel reversibly in a dose-dependent manner. The second 328-pS Cl- channel had a linear current-voltage relationship and permeability ratio (Cl-/Na+) of 5-6. This channel became less active with increasing polarizations and inactive beyond +/- 50 mV. DIDS blocked the channel irreversibly. The channel had multiple subconductance states. The third 15-pS Cl- channel was least frequently observed and least voltage sensitive among the Cl- channels. Intracellular Ca2+ or pH affected none of the three Cl- channels. All three Cl- channels had a latent period before being observed, suggesting inhibitory factor(s) present in situ. Activation of the cells with interferon-gamma, interferon-alpha A or 12-O-tetradecanoylphorbol-13-acetate (TPA) caused no change in the properties of any of the channels.
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Affiliation(s)
- T Kanno
- First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan
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32
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Frizzell RA, Halm DR. Chapter 8 Chloride Channels in Epithelial Cells. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1990. [DOI: 10.1016/s0070-2161(08)60234-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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33
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Berrier C, Coulombe A, Houssin C, Ghazi A. A patch-clamp study of ion channels of inner and outer membranes and of contact zones of E. coli, fused into giant liposomes. Pressure-activated channels are localized in the inner membrane. FEBS Lett 1989; 259:27-32. [PMID: 2480919 DOI: 10.1016/0014-5793(89)81486-3] [Citation(s) in RCA: 101] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Inner and outer membranes of Escherichia coli and contact zones were isolated and fused separately with giant liposomes amenable to patch-clamp recording. Different types of large pressure-activated channels were localized in the inner membrane fraction which also contained smaller, pressure-insensitive channels. The outer membrane contained pressure-insensitive channels with large conductances and long opening and closing times which are likely to be porins. Large channels were also observed in contact zones.
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Affiliation(s)
- C Berrier
- Laboratoire des Biomembranes, URA CNRS 1116, Orsay, France
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34
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Schmid A, Burckhardt G, Gögelein H. Single chloride channels in endosomal vesicle preparations from rat kidney cortex. J Membr Biol 1989; 111:265-75. [PMID: 2481041 DOI: 10.1007/bf01871011] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Endocytotic vesicles from rat kidney cortex, isolated by differential centrifugation and enriched on a Percoll gradient, contain both an electrogenic H+ translocation system and a conductive chloride pathway. Using the dehydration/rehydration method, we fused vesicles of enriched endosomal vesicle preparations and thereby made them accessible to the patch-clamp technique. In the fused vesicles, we observed Cl- channels with a single-channel conductance of 73 +/- 2 pS in symmetrical 140 mM KCl solution (n = 25). The current-voltage relationship was linear in the range of -60 to +80 mV, but channel kinetic properties depended on the clamp potential. At positive potentials, two sublevels of conductance were discernible and the mean open time of the channel was 10-15 msec. At negative voltages, only one substate could be resolved and the mean open time decreased to 2-6 msec. Clamp voltages more negative than -50 mV caused reversible channel inactivation. The channel was selective for anions over cations. Ion substitution experiments revealed an anion permeability sequence of Cl- = Br- = I- greater than SO4(2-) approximately F-. Gluconate, methanesulfonate and cyclamate were impermeable. The anion channel blockers 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 1.0 mM) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB, 0.1 mM) totally inhibited channel activity. Comparisons with data obtained from radiolabeled Cl(-)-flux measurements and studies on the H+ pump activity in endocytotic vesicle suspensions suggest that the channel described here is involved in maintenance of electroneutrality during ATP-driven H+ uptake into the endosomes.
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Affiliation(s)
- A Schmid
- Max-Planck-Institut für Biophysik, Frankfurt/Main, Federal Republic of Germany
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35
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Petersen OH. Does inositol tetrakisphosphate play a role in the receptor-mediated control of calcium mobilization? Cell Calcium 1989; 10:375-83. [PMID: 2670241 DOI: 10.1016/0143-4160(89)90063-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The evidence for and against an important role for inositol 1,3,4,5 tetrakisphosphate (Ins 1,3,4,5 P4) in receptor-mediated Ca2+ mobilization is reviewed. Data obtained from patch-clamp whole-cell current recording studies on internally perfused exocrine acinar cells show that the acetylcholine (ACh)-evoked sustained increase in Ca2+-dependent K+ current caused by an increase in [Ca2+]i cannot be mimicked by internal application of inositol 1,4,5-trisphosphate (Ins 1,4,5 P3), but only by a combination of Ins 1,4,5 P3 and Ins 1,3,4,5 P4. The sustained response evoked by Ins 1,4,5 P3 + Ins 1,3,4,5 P4 is dependent on the presence of external Ca2+ as is the effect of ACh. Only those inositol trisphosphates able to evoke Ca2+ release from internal stores can support the action of Ins 1,3,4,5 P4 in evoking responses that are acutely dependent on extracellular Ca2+ (Ca2+ influx). The various arguments presented against an involvement of Ins 1,3,4,5 P4 are discussed. The main point emerging is that most studies are inadequately controlled and it is concluded that there is a strong need for whole-cell current recording studies combined with pipette fluid exchange to be carried out in many more systems. The major problem in this field is that the precise site and mechanism of action of Ins 1,3,4,5 P4 are unknown and that the pathway for Ca2+ uptake during receptor activation is inadequately defined.
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Affiliation(s)
- O H Petersen
- MRC Secretory Control Research Group, Physiological Laboratory, University of Liverpool, UK
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36
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Thévenod F, Kemmer TP, Christian AL, Schulz I. Characterization of MgATP-driven H+ uptake into a microsomal vesicle fraction from rat pancreatic acinar cells. J Membr Biol 1989; 107:263-75. [PMID: 2469802 DOI: 10.1007/bf01871941] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In microsomal vesicles, as isolated from exocrine pancreas cells, MgATP-driven H+ transport was evaluated by measuring H+-dependent accumulation of acridine orange (AO). Active H+ uptake showed an absolute requirement for ATP with simple Michaelis-Menten kinetics (Km for ATP 0.43 mmol/liter) with a Hill coefficient of 0.99. H+ transport was maximal at an external pH of 6.7, generating an intravesicular pH of 4.8. MgATP-dependent H+ accumulation was abolished by protonophores, such as nigericin (10(-6) mol/liter) or CCCP (10(-5) mol/liter), and by inhibitors of nonmitochondrial H+ ATPases, such as NEM or NBD-Cl, at a concentration of 10(-5) mol/liter. Inhibitors of both mitochondrial and nonmitochondrial H+ pumps, such as DCCD (10(-5) mol/liter) or Dio 9 (0.25 mg/ml), reduced microsomal H+ transport by about 90%. Vanadate (2 x 10(-3) mol/liter), a blocker of those ATPases, which form a phosphorylated intermediate, did not inhibit H+ transport. The stilbene derivative DIDS (10(-4) mol/liter), which inhibits anion transport systems, abolished H+ transport completely. MgATP-dependent H+ transport was found to be anion dependent in the sequence Cl- greater than Br- greater than gluconate-; in the presence of SO2-4, CH3COO- or No-3, no H+ transport was observed. MgATP-dependent H+ accumulation was also cation dependent in the sequence K+ greater than Li+ greater than Na+ = choline+. As shown by dissipation experiments in the presence of different ion gradients and ionophores, both a Cl- and a K+ conductance, as well as a small H+ conductance, were found in the microsomal membranes. When membranes containing the H+ pump were further purified by Percoll gradient centrifugation (ninefold enrichment compared to homogenate), no correlation with markers for endoplasmic reticulum, mitochondria, plasma membranes, zymogen granules or Golgi membranes was found. The present data indicate that the H+ pump located in microsomes from rat exocrine pancreas is a vacuolar- or "V" -type H+ ATPase and has most similarities to that described in endoplasmic reticulum, Golgi apparatus or endosomes.
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Affiliation(s)
- F Thévenod
- Max-Planck-Institut für Biophysik, Frankfurt/Main, Federal Republic of Germany
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