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  • 1
    Electronic Resource
    Electronic Resource
    Evidence for two K+ currents activated upon hyperpolarization ofParamecium tetraurelia (1990)
    Springer
    The journal of membrane biology 115 (1990), S. 41-50 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869104
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  • 2
    Electronic Resource
    Electronic Resource
    Calmodulin defects cause the loss of Ca2+-dependent K+ currents in two pantophobiac mutants ofParamecium tetraurelia (1990)
    Springer
    The journal of membrane biology 115 (1990), S. 51-60 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869105
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  • 3
    Electronic Resource
    Electronic Resource
    Interactions between mutants with defects in two Ca2+-dependent K+ currents ofParamecium tetraurelia (1990)
    Springer
    The journal of membrane biology 115 (1990), S. 61-69 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869106
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Interactions between gene products involved in divalent cation transport in Saccharomyces cerevisiae (1994)
    Springer
    Molecular genetics and genomics 244 (1994), S. 303-311 
    Details
    ISSN: 1617-4623
    Keywords: Metal homeostasis ; Metal resistance ; Transport ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The COT1 and ZRC1 genes of Saccharomyces cerevisiae are structurally related dosage-dependent suppressors of metal toxicity. COT1 confers increased tolerance to high levels of cobalt; ZRC1 confers increased tolerance to high levels of zinc. The two genes are not linked and have been mapped; COT1 to chromosome XV and ZRC1 to chromosome XIII. Phenotypes related to metal homeostasis have been examined in strains with varied COT1 and ZRC1 gene doses. Overexpression of COT1 confers tolerance to moderately toxic levels of zinc and ZRC1 confers tolerance to moderately toxic levels of cobalt. Strains that carry null alleles at both loci are viable. The metal-hypersensitive phenotypes of mutations in either gene are largely unaffected by changes in dosage of the other. COT1 and ZRCI function independently in conferring tolerance to their respective metals, yet the uptake of cobalt ions by yeast cells is dependent on the gene dosage of ZRC1 as well as of COT1 Strains that overexpress ZRC1 have increased uptake of cobalt ions, while ZRCI null mutants exhibit decreased cobalt uptake. The defects in cobalt uptake due to mutations at COT1 and ZRC1 are additive, suggesting that the two genes are responsible for the majority of cobalt and zinc uptake in yeast cells. The function of either gene product seems to be more important in metal homeostasis than is the GRR1 gene product, which is also involved in metal metabolism. Mutations in the GRR1 gene have no effect on the cobalt-related phenotypes of strains that have altered gene dosage of either COT1 or ZRC1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285458
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