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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 59 (1981), S. 179-190 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Under voltage clamp, a mutant ofParamecium tetraurelia (teaB) shows a shift in the positive direction of the voltage sensitivity of the Ca conductance and the depolarization inactivation curve by 10 mV with no change in the total conductance. This effect can be mimicked in the wild type by the addition of external Ca2+ or Mg2+. The mutation also shifts the resting potential and the voltage sensitivities of the delayed rectification (depolarization-sensitive) K conductance and the anomalous rectification (hyperpolarization-sensitive) K conductance in the positive direction to a similar extent. This systematic shift of channel voltage sensitivities is best explained by the reduction of the surface negative charges of the membrane due to the mutation.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 112 (1989), S. 267-275 
    ISSN: 1432-1424
    Keywords: Escherichia coli ; outer membrane ; ion channel ; patch clamp ; porin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A voltage-sensitive, cation-selective ion channel ofEscherichia coli has been reconstituted into liposomes and studied with the patch-clamp method. The single channel conductance was 91 pS in symmetric solutions of 150mm KCl. Many channels were open most of the time, with frequent brief transitions to closed levels. Multiple conducting units could close and reopen simultaneously, and this apparent cooperativity in gating was increases with depolarizing voltages. Above a voltage threshold, the channels closed irreversibly, often in groups.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 115 (1990), S. 41-50 
    ISSN: 1432-1424
    Keywords: inward rectification ; voltage-dependent K+ current ; Ca2+-dependent K+ current ; Paramecium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Hyperpolarization of voltage-clampedParamecium tetraurelia in K+ solutions elicits a complex of Ca2+ and K+ currents. The tail current that accompanies a return to holding potential (−40 mV) contains two K+ components. The tail current elicited by a step to −110 mV of ≥50-msec duration contains fast-decaying (τ≈3.5 msec) and slow-decaying (τ≈20 msec) components. The reversal potential of both components shifts by 55–57 mV/10-fold change in external [K+], suggesting that they represent pure K+ currents. The dependence of the relative amplitudes of the two tail currents on duration of hyperpolarization suggests that the slow K+ current activates slowly and is sustained, whereas the fast current activates rapidly during hyperpolarization and then rapidly inactivates. Iontophoretic injection of a Ca2+ chelator, EGTA, specifically reduces slow tail-current amplitude without affecting the fast tail component. Both K+ currents are inhibited by extracellular TEA+ in a concentration-dependent, noncooperative manner, whereas the fast K+ current alone is inhibited by 0.7mm quinidine.
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  • 4
    ISSN: 1432-1424
    Keywords: calmodulin ; mutation ; ion currents ; Paramecium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Two behavioral mutants ofParamecium tetraurelia, pantophobiacs A1 and A2, have single amino acid defects in the structure of calmodulin. The mutants exhibit several major ion current defects under voltage clamp: (i) the Ca2+-dependent K+ current activated upon depolarization ofParamecium is greatly reduced or missing in both mutants, (ii) both mutants lack a Ca2+-dependent K+ current activated upon hyperpolarization, and (iii) the Ca2+-dependent Na+ current is significantly smaller in pantophobiac A1 compared with the wild type, whereas this current is slightly increased in pantophobiac A2. Other, minor defects include a reduction in peak amplitude of the depolarization-activated Ca2+ current in pantophobiac A2, increased rates of voltage-dependent inactivation of this Ca2+ current in both pantophobiac A1 and pantophobiac A2, and an increase in the time required for the hyperpolarization-activated Ca2+ current to recover from inactivation in the pantophobiacs. The diversity of the pantophobiac mutations' effects on ion current function may indicate specific associations of calmodulin with a variety of Ca2+-related ion channel species inParamecium.
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  • 5
    ISSN: 1432-1424
    Keywords: calmodulin ; Ca2+-dependent K+ channels ; ion channel regulation ; mutations ; Paramecium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Paramecium tetraurelia possesses two Ca2+-dependent K+ currents, activated upon depolarizationI K(Ca,d), or upon hyperpolarizationI K(Ca,h). The two currents are mediated by pharmacologically distinct ion channel populations. Three mutations ofP. tetraurelia affect these current.s Pantophobiac A mutations (pntA) cause calmodulin sequence defects, resulting in the loss of both Ca2+-dependent K+ currents. A second mutation, TEA-insensitive A (teaA), greatly enhancesI K(Ca,d) but has no affect onI K(Ca,h). A third mutation,restless (rst), also increasesI K(Ca,d) slightly, but its principle effect is in causing an early activation ofI K(Ca,h). Interactions between the products of these three genes were investigated by constructing three double mutants. BothteaA andrst restoreI K(Ca,d) andI K(Ca,h) in pantophobiac A1, but the phenotypes ofteaA andrst are not corrected by a second mutation. These observations may indicate a role for the gene products ofteaA andrst in regulating the activity ofI K(Ca,d) andI K(Ca,h), respectively.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 43 (1978), S. 169-185 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Voltage clamp studies show that the wild-type membrane ofParamecium tetraurelia contains a conductance component which is sensitive to hyperpolarization. This component manifests itself as “anomalous”, or “inward going”, rectification of membrane voltage in response to applied constant current pulses and as a “hyperpolarizing spike” when no K is added to the external solution (Y. Satow, C. Kung, 1977.J. Comp. Physiol. 119∶99). Like the conductances which underlie anomalous rectification in other cells, the hyperpolarization-sensitive conductance inParamecium is specific for K, and the magnitude of the voltage-dependent conductance change depends not only on voltage but also on external potassium concentration. The internal potassium ion concentration ofParamecium is calculated to be between 17 and 18mm.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 28 (1976), S. 277-294 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Two heat-sensitive “pawn” mutants ofParamecium aurelia are capable of avoiding reactions when grown at 23°C but not at 35°C. Electrophysiological analyses show that Ca activation is reduced in the mutants even when they are grown at 23°C. The maximal rate of rise and the peak of the evoked action potential (Ca-spike) in the mutants are smaller than those of wild type in a K-solution. After suppression of K conductance by either TEA+ or Ba++, the action potentials of the mutants peak at the same level as that of wild type. However, the maximal rate of rise of the mutants remains only about half that of wild type. Thus, the mutations affect Ca activation but not K activation. Incubation at a high temperature (35°C) further reduces Ca activation to almost zero in the mutants but has little or no effect on wild type. This almost complete loss of Ca activation explains the lack of avoiding reactions when the mutants are grown at high temperatures. A double mutant containing two heat-sensitive mutations shows extremely reduced Ca activation even when grown at 23°C.
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  • 8
    ISSN: 1432-1424
    Keywords: mechanosensitive channel ; outer membrane ; Escherichia coli/kw] ; lipoprotein ; membrane protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The activity of the mechanosensitive (MS) ion channels in membrane patches, excised fromE. coli spheroplasts, was analyzed using the patch-clamp technique. Outer membranes from a mutant lacking the major lipoprotein (Lpp) and its wildtype parent were examined. The MS-channel activities in the wild-type membrane rarely revealed substates at the time resolution used. These channels showed a stretch sensitivity indicated by the IISP (the suction for ane-fold increase in channel open probability) of 4.9 mm Hg suction. The MS-channel activities oflpp included a prominent substate and showed a weaker mechano-sensitivity with an 1/S p of 10.0 mm Hg. Whereas small amphipaths (chlorpromazine, trinitrophenol) or a larger amphipath (lysolecithin) all activated the MS channel in the wild-type membrane under minimal suction, only the larger lysolecithin could activate the MS channel in thelpp membranes. After lysolecithin addition, thelpp membrane became more effective in transmitting the stretch force to the MS channel, as indicated by a steepening of the Boltzmann curve. We discuss one interpretation of these results, in which the major lipoprotein serves as a natural amphipath inserted in the inner monolayer and the loss of this natural amphipath makes the bilayer less able to transmit the gating force.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 98 (1987), S. 145-155 
    ISSN: 1432-1424
    Keywords: calcium-dependent K+ current ; mutant ; Paramecium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The membrane currents of wild typeParamecium tetraurelia and the behavioral mutantteaA were analyzed under voltage clamp. TheteaA mutant was shown to have a greatly increased outward current which was blocked completely by the combined use of internally delivered Cs+ and external TEA+. This, along with previous work (Satow, Y., Kung, C., 1976,J. Exp. Biol. 65:51–63) identified this as a K+ current. It was further found to be a calcium-activated K+ current since this increased outward K+ current cannot be elicited when the internal calcium is buffered with injected EGTA. The mutationpwB, which blocks the inward calcium current, also blocks this increased outward K+ current inteaA. This shows that this mutant current is activated by calcium through the normal depolarization-sensitive calcium channel. While tail current decay kinetic analysis showed that the apparent inactivation rates for this calcium-dependent K+ current are the same for mutant and wild type, theteaA current activates extremely rapidly. It is fully activated within 2 msec. This early activation of such a large outward current causes a characteristic reduction in the amplitude of the action potential of theteaA mutant. TheteaA mutation had no effect on any of the other electrophysiological parameters examined. The phenotype of theteaA mutant is therefore a general decrease in responsiveness to depolarizing stimuli because of a rapidly activating calcium-dependent K+ current which prematurely repolarizes the action potential.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 119 (1994), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Mutations at three loci in Saccharomyces cerevisiae have been shown to confer increased sensitivity to the antimalarial and antiarrhythmic alkaloid, quinidine. Two of these groups are composed of strains carrying recessive mutations, the other group contains two dominant alleles. The largest complementation group has been designated QDS1, for increased quinidine-sensitivity. Exposure of qds1 cells to lethal concentrations of quinidine results in a novel small-budded terminal morphology in about 70% of the cells in the culture. Strains which carry qds1 alleles share other pleiotropic phenotypes. qds1 mutants are incapable of mating as α but not a cells, due to a defect in α-factor production. Homozygous diploid qds1 strains cannot sporulate. Genetic evidence indicates that QDS1 is allelic to KEX2, a precursor processing protease. Loss of QDS1 / KEX2 function results in quinidine sensitivity.
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