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  • 1
    Electronic Resource
    Electronic Resource
    Halide and Alkyl Phenols Block Volume-Sensitive Chloride Channels in Human Glial Cells (U-138MG) (1998)
    Springer
    The journal of membrane biology 162 (1998), S. 191-200 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Chloride channels — Volume regulation — Patch clamp — Ion channel blockers — Phenol derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Swelling of cells in hypotonic media activates a volume-sensitive Cl channel with well-known characteristics, but its structure and its regulation are still largely undetermined. It also has many inhibitors and most of them are also blocking other types of Cl channels. The numerous inhibitors of Cl channels have apparently no structural relationship among them. The purpose of this study was to try to determine the most simple molecules that could block these channels and identify some common properties among inhibitors. From the 37 new molecules that were studied, it was found that simple halide phenols like trichloro and triiodophenols could block these channels in the micromolar range. Also alkyl phenols, like butylphenols, are very sensitive blockers, comparable to other well-known blockers. But acidic halide phenols or nitrophenols are poor blockers. Also neutral polyphenols are more sensitive than acidic polyphenols. All these results indicate that the common basis for blocking these Cl channels is a phenol with hydrophobic groups, like short alkyl chains or an additional phenyl ring, attached to some of its sites, preferably sites 3-4-5. These results identify a new family of Cl channel blockers and hopefully improve our understanding of the blocking mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900356
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of a Chloride-Selective Channel from Rough Endoplasmic Reticulum Membranes of Rat Hepatocytes: Evidence for a Block by Phosphate (1997)
    Springer
    The journal of membrane biology 159 (1997), S. 219 -229 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Endoplasmic reticulum — Cl− channel — Phosphate — Bilayer — Vesicles — Cl− Channel in ER
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. We have characterized the conduction and blocking properties of a chloride channel from rough endoplasmic reticulum membranes of rat hepatocytes after incorporation into a planar lipid bilayer. Our experiments revealed the existence of a channel with a mean conductance of 164 ± 5 pS in symmetrical 200 mm KCl solutions. We determined that the channel was ten times more permeable for Cl− than for K+, calculated from the reversal potential using the Goldman-Hodgkin-Katz equation. The channel was voltage dependent, with an open probability value ranging from 0.9 at −20 mV to 0.4 at +60 mV. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to zero current level. Our results showed a decrease of the channel mean open time combined with an increase of the channel mean closed time at positive potentials. An analysis of the dwell time distributions for the open and closed intervals led to the conclusion that the observed fluctuation pattern was compatible with a kinetic scheme containing a single open state and a minimum of three closed states. The permeability sequence for test halides determined from reversal potentials was Br− 〉 Cl− 〉 I−≈ F−. The voltage dependence of the open probability was modified by the presence of halides in trans with a sequence reflecting the permeability sequence, suggesting that permeant anions such as Br− and Cl− have access to an internal site capable of controlling channel gating. Adding NPPB to the cis chamber inhibited the channel activity by increasing fast flickering and generating long silent periods, whereas channel activity was not affected by 50 μm DNDS in trans. The channel was reversibly inhibited by adding phosphate to the trans chamber. The inhibitory effect of phosphate was voltage-dependent and could be reversed by addition of Cl−. Our results suggest that channel block involves the interaction of HPO2− 4 with a site located at 70% of the membrane span.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900285
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  • 3
    Electronic Resource
    Electronic Resource
    Oscillatory activation of calcium-dependent potassium channels in HeLa cells induced by histamine H1 receptor stimulation: A single-channel study (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 199-208 
    Details
    ISSN: 1432-1424
    Keywords: oscillation ; histamine ; H1 receptor ; Ca2+-activated potassium channel ; patch clamp ; HeLa cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have used the patch-clamp method (O.P. Hamill et al.,Pfluegers Arch.,391:85–100, 1981) in order to investigate the activation pattern of a calcium-dependent potassium channel following H1 receptor stimulation in HeLa cells. Our results essentially indicate that the stimulation of H1 receptors by exogenous histamine at concentrations greater than 1 μm induces an oscillatory activation pattern of calcium-dependent potassium channels characterized by the occurrence of channel current bursts separated by long silent periods. It was also found that the occurrence of these bursts could be directly correlated with transmembrane potential oscillations, the latter being the resulting effect of the calcium-dependent potassium channel synchronous openings. In addition, the cyclic activation of the calciumdependent potassium channels could be initiated by the addition of histamine to a calcium-free external medium, indicating that the stimulation of the H1 receptors in HeLa cells is mainly related to the release of calcium from internal stores. Finally, the membrane-permeable cyclic AMP analog dibutyryl cyclic AMP was found to be ineffective in initiating single-channel events such as those triggered by exogenous histamine. It is proposed that the oscillatory activation of the calcium-dependent potassium channels in HeLa cells results from a repetitive transient increase in cytosolic free calcium concentration consequent to the H1 receptor stimulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869302
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  • 4
    Electronic Resource
    Electronic Resource
    Activation of amino acid diffusion by a volume increase in cultured kidney (MDCK) cells (1992)
    Springer
    The journal of membrane biology 130 (1992), S. 83-90 
    Details
    ISSN: 1432-1424
    Keywords: amino acid ; volume regulation ; MDCK cells ; hyposmolarity ; kidney cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary When MDCK cells are cultured in MEM, they maintain a high concentration of three amino acids: glutamate (25mm), taurine (19 mm) and glycine (9 mm). With incubation of the cells in hypotonic media, the contents of these amino acids measured by HPLC are reduced in different time courses: taurine decreases most rapidly, followed by glutamate and glycine. All these losses are Na+ independent. To determine the transport mechanism activated by the hypotonic media, increasing external concentrations reaching 60 mm for nine different amino acids in Na+-free media were tested separately. For the five neutral (zwitterionic) amino acids, taurine, glycine, alanine, phenylalanine and tryptophan, cell contents increased linearly with external concentrations in hypotonic media, whereas in isotonic media only a slight rise was observed. The two anionic amino acids, glutamate and aspartate, were also increased linearly with their external concentrations in hypotonic media, but the changes were lower than those found for neutral amino acids. The presence of a negative membrane potential was responsible for this behavior since, using a K+ hypotonic medium which clamps the potential to zero, the glutamate content was found to increase linearly with an amplitude similar to the one observed for neutral amino acid. When external concentrations of two cationic amino acids, arginine and lysine, were increased in hypotonic media, only a small change, similar to that in isotonic media, was observed. These results indicate that a diffusion process for neutral and anionic amino acids is activated by a volume increase and it is suggested that an anion channel is involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233740
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of anisotonic media on volume, ion and amino-acid content and membrane potential of kidney cells (MDCK) in culture (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 83-96 
    Details
    ISSN: 1432-1424
    Keywords: volume regulation ; membrane potential ; membrane transport ; kidney cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Effects of anisotonic media on a monolayer of confluent kidney cells in culture (MDCK) were studied by measuring: cell thickness and cross-section changes, ion and amino-acid content and membrane potential. The volume was also determined with cells in suspension. When cells in a monolayer were incubated in hypotonic media, the lateral and the apical membranes were rapidly stretched. Afterwards the lateral membranes returned to their initial state while the apical membranes remained stretched. This partial regulatory volume decrease (RVD) was verified with cells in suspension. RVD was accompanied by a loss of K+, Cl− and amino acids, but there was no loss of inorganic phosphate. Also a transient hyperpolarization of the membrane potential was observed, suggesting an increase of the K+ conductance during RVD. Upon restoring the isotonic medium, a regulatory volume increase (RVI) was observed accompanied by a rapid Na+ and Cl− increase and followed by a slow recovery of the initial K+ and Na+ content while amino acids remained at their reduced content. A transient depolarization of the membrane potential was measured during this RVI, suggesting that Na+ and Cl− conductance could have increased. In hypertonic media, only a small and slow RVI was observed accompanied by an increase in K+ and Cl− content but without any change of membrane potential. Quinine partly inhibited RVD in hypotonic media with cells in a monolayer while inhibiting RVD completely with cells in suspension. Incubation during four hours in a Ca2+ free medium had no effect on RVD. Furosemide and amiloride had no effect on RVD and RVI. Volume regulation, RVD or RVI, was not affected by replacing Cl− by nitrate. When cells in a monolayer were incubated in a hypotonic K2SO4 medium, no RVD was observed. From these results, it seems that MDCK cells in a confluent monolayer regulate their volume by activating specific ion and amino-acid transport pathways. Selective K+ and Na+ conductances are activated during RVD and RVI, while the activated anion conductance has a low selectivity. The controlling mechanism might not be the free intracellular Ca2+ concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209143
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  • 6
    Electronic Resource
    Electronic Resource
    Errata (1972)
    Springer
    The journal of membrane biology 9 (1972), S. 104-104 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868046
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  • 7
    Electronic Resource
    Electronic Resource
    Single-channel analysis of the potassium permeability in HeLa cancer cells: Evidence for a calcium-activated potassium channel of small unitary conductance (1986)
    Springer
    The journal of membrane biology 92 (1986), S. 269-282 
    Details
    ISSN: 1432-1424
    Keywords: potassium channel ; inward rectification ; path clamp ; Ca2+ activated ; HeLa cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cell-attached and inside-out patch-clamp experiments (O.P. Hamill et al.,Pfluegers Arch. 391: 85–100, 1981) were undertaken in order to characterize the molecular mechanisms responsible for the calcium-dependent potassium permeability observed in HeLa cancer cells. Our result essentially indicate that the HeLa cell external membrane contains potassium channels whose activity can be triggered within an internal calcium concentration range of 0.1 to 1 μm. This particular channel was found to behave as an inward rectifier in symmetrical 200mm KCl with a conductance of 50 and 10 pS at large negative and large positive membrane potentials, respectively.I/V curves were also measured in 10, 20, 75, 200 and 300mm KCl and the data interpreted in terms of a one-site-two-barrier model. The channel activity appeared to be nearly voltage independent within the voltage range −100 to +100mV, an increase ofP o, the open channel probability, being observed at large negative potentials only. In addition, the results obtained from inside-out experiments on the relationship betweenP o and the cytoplasmic freecalcium concentration have led to conclude that four calcium ions are probably required in order to open the channel. In this regard it was found that an increase of the internal free-calcium level affects more the number of channel openings per second than the actual channel mean lifetime. Finally, it is concluded following a time interval distribution analysis, that this particular channel has at least three closed states and two open states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869395
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  • 8
    Electronic Resource
    Electronic Resource
    Amino acid current through anion channels in cultured human glial cells (1995)
    Springer
    The journal of membrane biology 147 (1995), S. 35-44 
    Details
    ISSN: 1432-1424
    Keywords: Amino acids ; Chloride channels ; Glial ; cells ; Volume regulation ; Glutamate ; Neurotransitters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract During volume regulation in hypotonic media, glial cells release a large portion of their amino acids. These amino acid losses appear to be mediated by a diffusion type of transport and a swelling-activated chloride channel seems to be involved. The objective of this project was to provide direct evidence that amino acids could diffuse through a Cl− channel. Using a human glial cell line, Cl− currents activated in hypotonic media were measured in whole-cell patch clamp. To measure the currents produced by amino acids, it was necessary to increase the pH of external solutions to basic values reaching 9.6 and 10.0 to raise the concentration of the anionic form of these amino acids. Introducing external hypotonic media containing high concentrations of amino acids, like glycine, taurine, glutamine and glutamate, it was possible to measure their respective current-voltage curves with NMDG-Cl-filled pipettes. From the reversal potentials, their permeability ratios with respect to chloride were determined. It was found that the low molecular weight amino acids, like glycine, were most permeant, while the larger ones, like glutamine, had a lower permeability with respect to chloride. The amino acids with two carboxyl groups, like glutamate, had a much lower permeability ratio. The reversal potentials for some metabolites, like lactate and malate were also measured for comparison. These results demonstrate that amino acids can diffuse through anion channels and that activation of these channels in pathological conditions could be at least partly responsible for the observed increase in external amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235396
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  • 9
    Electronic Resource
    Electronic Resource
    Single channel K+ currents from HeLa cells (1983)
    Springer
    The journal of membrane biology 74 (1983), S. 41-49 
    Details
    ISSN: 1432-1424
    Keywords: HeLa cells ; single channel ; patch clamp ; potassium ; inward reetification ; Ca++ activated
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The extracellular patch-clamp technique was used in order to investigate the presence of ionic channels in HeLa cells, a well-known cultured cell type obtained from an epidermoid carcinoma of the cervix. Under Gigohm-seal conditions, discrete current jumps could be observed with patch electrodes containing KCl. These channels were found to be mainly permeable to K+ and showed multiple levels of conductance. From single-channelI–V curve measurements, a strong rectification effect, characterized by a large inward and no detectable outward current, was observed. For negative membrane potentials (0 to −90 mV), the measured current-voltage relationship was found to be mostly linear, corresponding to a single-channel conductance of 40 pS. An analysis of some selected time records has revealed in addition that the probability of the channel to be in the open state was a function of the KCl concentration in the patch pipette.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870593
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  • 10
    Electronic Resource
    Electronic Resource
    Substrate and inhibitor specificity of anion exchangers on the brush border membrane of rabbit ileum (1985)
    Springer
    The journal of membrane biology 88 (1985), S. 199-204 
    Details
    ISSN: 1432-1424
    Keywords: anion exchange ; Cl∶HCO3 exchange ; SO4∶OH exchange ; Ox∶Cl exchange ; brush border membrane ; ileum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In previous studies we have found that several anions can be transported by an exchange process in rabbit ileal brush border membranes. We demonstrated exchanges of Cl for OH or HCO3, SO4 for OH, oxalate for OH, and oxalate for Cl. The purpose of these studies was to determine the number of distinct carriers mediating these exchanges. We utilized substrate and inhibitor specificity studies to distinguish between different anion exchange transporters. We conclude that SO4∶OH and oxalate: OH exchange occur on the same carrier because: (i) pH-gradient stimulated transport of both14C-oxalate and35SO4 were equally sensitive tocis-inhibition by unlabeled SO4 or oxalate; and (ii) both were inhibited equally by K. We conclude that oxalate: OH and oxalate: Cl exchanges occur on different carriers because: (i) Cl or SO4 caused unequalcis-inhibition of these two exchanges; and (ii) as compared to oxalate: Cl exchange, oxalate: OH exchange was more sensitive to inhibition by probenecid and K and less sensitive to inhibition by bumetanide. Finally, we conclude that oxalate: Cl exchange and Cl∶HCO3 exchange occur on different carriers because: (i) Cl∶HCO3 exchange was almost completely insensitive tocis-inhibition by oxalate; and (ii) oxalate: Cl exchange was more sensitive to inhibition by DIDS and bumetanide than Cl∶HCO3 exchange. Thus we have found that there are at least three separate anion exchangers on rabbit ileal brush border: (i) a Cl∶HCO3 exchanger; (ii) a SO4∶OH exchanger, which also transports oxalate; and (iii) an oxalate: Cl exchanger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868433
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