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1

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A calcium-dependent potassium current is increased by a single-gene mutation inParamecium (1987)

Hennessey, Todd M. ; Kung, Ching

Springer

The journal of membrane biology 98 (1987), S. 145-155

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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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2

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Growth of Paramecium tetraurelia in Bacterized, Monoxenic Cultures (1987)

ENRIGHT, WILLIAM J. ; HENNESSEY, TODD M.

Oxford, UK : Blackwell Publishing Ltd

The @journal of eukaryotic microbiology 34 (1987), S. 0

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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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3

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Chemosensory Adaptation to Lysozyme and GTP Involves Independently Regulated Receptors in Tetrahymena thermophila (1997)

KURUVILLA, HEATHER G. ; KIM, MARK Y. ; HENNESSEY, TODD M.

Oxford, UK : Blackwell Publishing Ltd

The @journal of eukaryotic microbiology 44 (1997), S. 0

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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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4

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Chemorepellents in Paramecium and Tetrahymena (1995)

FRANCIS, JOSEPH T. ; HENNESSEY, TODD M.

Oxford, UK : Blackwell Publishing Ltd

The @journal of eukaryotic microbiology 42 (1995), S. 0

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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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5

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A heat-induced depolarization ofParamecium and its relationship to thermal avoidance behavior (1983)

Hennessey, Todd M. ; Saimi, Yoshiro ; Kung, Ching

Springer

Journal of comparative physiology 153 (1983), S. 39-46

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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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