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  • 1
    Electronic Resource
    Electronic Resource
    Electrophysiological evidence suggests a defective Ca2+ control mechanism in a newParamecium mutant (1987)
    Springer
    The journal of membrane biology 98 (1987), S. 275-283 
    Details
    ISSN: 1432-1424
    Keywords: Paramecium ; calcium ; cilia ; mutants ; Ca2+ pump ; Ca2+ buffering ; ion channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A new mutant ofParamecium tetraurelia, k-shyA, was characterized behaviorally and electrophysiologically. The mutant cell exhibited prolonged backward swimming episodes in response to depolarizing conditions. Electrophysiological comparison of k-shyA with wild type cells under voltage clamp revealed that the properties of three Ca2+-regulated currents were altered in the mutant. (i) The voltage-dependent Ca2+ current recovered from Ca2+-dependent inactivation two- to 10-fold more slowly than wild type. Ca2+ current amplitudes were also reduced in the mutant, but could be restored by EGTA injection. (ii) The decay of the Ca2+-dependent K+ tail current was slower in the mutant. (iii) The decay of the Ca2+-dependent Na+ tail current was also slower in the mutant. All other membrane properties studied, including the resting membrane potential and resistance and the voltage-sensitive K+ currents, were normal in k-shyA. Considered together, these observations are consistent with a defect in the ability of k-shyA to reduce the free intracellular Ca2+ concentration following stimulation. The possible targets of the genetic lesion and alternative explanations are discussed. The k-shy mutants may provide a useful tool for molecular and physiological analyses of the regulation of Ca2+ metabolism inParamecium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871189
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  • 2
    Electronic Resource
    Electronic Resource
    A calcium-dependent potassium current is increased by a single-gene mutation inParamecium (1987)
    Springer
    The journal of membrane biology 98 (1987), S. 145-155 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872127
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  • 3
    Electronic Resource
    Electronic Resource
    Growth of Paramecium tetraurelia in Bacterized, Monoxenic Cultures (1987)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 34 (1987), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Wild type and mutant Paramecium tetraurelia were grown in monoxenic cultures by first growing Enterobacter aerogenes on a defined medium and then adding the Paramecium to the stationary phase bacterial culture. The bacterial growth was proportional to the concentration of the carbon source (citrate), and the Paramecium growth was dependent upon both the bacterial density and the starting density of Paramecium. The behavior, electrophysiological properties, ciliary lipid composition, and growth characteristics were similar to the commonly used bacterized medium (Cerophyl) except that 5–10 times greater Paramecium yields were reliably obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1987.tb03149.x
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  • 4
    Electronic Resource
    Electronic Resource
    Chemosensory Adaptation to Lysozyme and GTP Involves Independently Regulated Receptors in Tetrahymena thermophila (1997)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 44 (1997), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . Chemosensory adaptation is seen in Tetrahymena thermophila following prolonged exposure (ten minutes) to micromolar concentrations of the chemorepellents lysozyme or guanosine triphosphate (GTP). Since these cells initially show repeated backward swimming episodes (avoidance reactions) in these repellents, behavioral adaptation is seen as a decrease in this repellent-induced behavior. The time course of this behavioral adaptation is paralleled by decreases in the extents of surface binding of either [32P]GTP or [3H]lysozyme in vivo. Scatchard plot analyses of repellent binding in adapted cells suggests the behavioral adaptation is due to a dramatic decrease in the number of surface binding sites, as represented by decreased Bmax values. The estimated KD values for nonadapted cells are 6.6 μM and 8.4 μM for lysozyme and GTP binding, respectively. Behavioral adaptation and decreased surface receptor binding are specific for each repellent. The GTP adapted cells (20 μM for ten minutes) still respond behaviorally to 50 μM lysozyme and bind [3H]lysozyme normally. Lysozyme adapted cells (50 μM for ten minutes) still bind [32P]GTP and respond behaviorally to GTP. All the behavioral and binding changes seen are also reversible (deadaptation). Neomycin was shown to be a competitive inhibitor of [3H]lysozyme binding and lysozyme-induced avoidance reactions, but it had no effect on either [32P]GTP binding or GTP-induced or avoidance reactions. These results are consistent with the hypothesis that there are two separate repellent receptors, one for GTP and the other for lysozyme, that are independently downregulated during adaptation to cause specific receptor desensitization and consequent behavioral adaptation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1997.tb05710.x
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  • 5
    Electronic Resource
    Electronic Resource
    Chemorepellents in Paramecium and Tetrahymena (1995)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 42 (1995), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Although Paramecium has been widely used as a model sensory cell to study the cellular responses to thermal, mechanical and chemoattractant stimuli, little is known about their responses to chemorepellents. We have used a convenient capillary tube repellent bioassay to describe 4 different compounds that are chemorepellents for Paramecium and compared their response with those of Tetrahymena. The classical Paramecium t-maze chemokinesis test was also used to verify that this is a reliable chemorepellent assay. The first two compounds, GTP and the oxidant NBT, are known to be depolarizing chemorepellents in Paramecium but this is the first report of them as repellents in Tetrahymena. The second two compounds, the secretagogue alcian blue and the dye cibacron blue, have not previously been described as chemorepellents in either of these ciliates. Two other compounds, the secretagogue AED and the oxidant cytochrome c, were found to be repellents to Paramecium but not to Tetrahymena. The repellent nature of each of these compounds is not related to toxicity because cells are completely viable in all of them. More importantly, all of these repellents are effective at micromolar to nanomolar concentrations, providing an opportunity to use them as excitatory ligands in future works concerning their membrane receptors and possible receptor operated ion channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1995.tb01544.x
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  • 6
    Electronic Resource
    Electronic Resource
    A heat-induced depolarization ofParamecium and its relationship to thermal avoidance behavior (1983)
    Springer
    Journal of comparative physiology 153 (1983), S. 39-46 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have recorded fromParamecium a membrane depolarization in response to heat. This heat-induced depolarization is graded with the magnitude of the temperature change and can trigger action potentials. The mechanism for the Ca-action potential, localized in the cilia, is not needed in generating the heat-induced depolarization, since a ciliary Ca-channel mutant (pwB) and a deciliated wild type both show the same magnitude of depolarization as an intact wild type. The direction and magnitude of change in the membrane potential in response to heat is affected by the initial level of the membrane potential. Conditions which depolarize the wild type decrease both the heat-induced depolarization and thermal avoidance behavior. A mutant with defective thermal avoidance behavior,teaB, is naturally less polarized at rest (Satow and Kung 1981) but can produce heat-induced depolarizations equal to that of the wild type if hyperpolarized to the wild-type levels by injection of constant current. Both the mutant and the wild type have apparent reversal potentials at −5 to −20 mV in 1 mmol/l Ca2+, above which the response to heat becomes a hyperpolarization. In both the wild type andteaB, the size of the heat-induced depolarization parallels the strength of the behavioral response to heat as measured by individual or population assays of thermal avoidance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00610340
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  • 7
    Electronic Resource
    Electronic Resource
    Mutants in paramecium tetraurelia defective in their axonemal response to calcium (1984)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 4 (1984), S. 283-295 
    Details
    ISSN: 0886-1544
    Keywords: axonemal mutants ; Ca++ response ; ciliary reversal ; electrophysiology ; models ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Six mutants of Paramecium tetraurelia, which display altered axonemal responses to Ca++, are described. The mutants, designated atalantas, are impaired in their ability to swim backward when stimulated by ions or heat; instead they spin very rapidly in one place. Three mutants, ataA1-3, are completely unable to swim backward. The three lines, however, can be distinguished from one another by their forward swimming velocities. The remaining three mutants are leaky. ataB swims backward briefly when stimulated, then stops and spins in place. ataC and ataD are extremely leaky and only display the spinning phenotype at elevated temperatures. An electrophysiological analysis reveals that all six mutants have normal membrane properties, including the Ca++ inward current under voltage clamp. When the membrane is disrupted so as to allow the axoneme free access to Ca++, wild-type cells swim backward, but the mutants do not. These data indicate the site(s) of lesion in the mutants is in the axoneme or in some step linking Ca++ influx and the axoneme, not within the ciliary membrane. These mutants may be useful in investigating the role of Ca++ in the regulation of axonemal motion.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970040406
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