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  • 1
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The deep roots and wide branches of the K+-channel family are evident from genome surveys and laboratory experimentation. K+-channel genes are widespread and found in nearly all the free-living bacteria, archaea and eukarya. The conservation of basic structures and mechanisms such as the K+ filter, the gate, and some of the gate's regulatory domains have allowed general insights on animal K+ channels to be gained from crystal structures of prokaryotic channels. Since microbes are the great majority of life's diversity, it is not surprising that microbial genomes reveal structural motifs beyond those found in animals. There are open-reading frames that encode K+-channel subunits with unconventional filter sequences, or regulatory domains of different sizes and numbers not previously known. Parasitic or symbiotic bacteria tend not to have K+ channels, while those showing lifestyle versatility often have more than one K+-channel gene. It is speculated that prokaryotic K+ channels function to allow adaptation to environmental and metabolic changes, although the actual roles of these channels in prokaryotes are not yet known. Unlike enzymes in basic metabolism, K+ channel, though evolved early, appear to play more diverse roles than revealed by animal research. Finding and sorting out these roles will be the goal and challenge of the near future.
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  • 2
    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.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 4
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Methods for mass transformation of Paramecium tetraurelia were established using plasmids bearing neomycin-resistance or calmodulin gene fragments. Phenotypic and molecular analyses showed that, although variable, up to 5% transformation can be achieved by electroporation. Concentrations of divalent cations Ca2- and Mg2+ in the electroporation medium were crucial for efficient transformation. Strong neomycin-resistance transformation using bioballistic particle bombardment with gold particles was observed. For both methods, hybridization to transformant DNA revealed plasmid signals consistent with macronuclear transformation and correlated with transformed phenotypes. Complementation of a known calmodulin gene mutation was also achieved by mass transformation. Possible sources of variation and the general utility of these methods are discussed.
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  • 5
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have generated a transformation marker for Paramecium using a Paramecium expression vector (pPXV) and the open reading frame (ORF) of the bacterial antibiotic resistance gene aminoglycoside 3'-phosphotransferase-II (APH-3'-II or neor) from the transposon Tn5. The expression vector contained a small multiple cloning site between the 5' and 3' non-coding regions of the calmodulin gene, and Tetrahymena telomere sequences for the stability of the plasmid in Paramecium. After the neor ORF was inserted, the plasmid was referred to as pPXV-NEO. Delivery of approximately 10–20 picoliters of linearized PXV-NEO at 〉 2000 copies/pl into the macronucleus effected 100% transformation. Southern and Northern blot hybridization showed the presence of neor-specific DNA and RNA, respectively, in all of the transformed clones but not in the untransformed clones. The degree of resistance to G-418, and the concentrations of neor-specific DNA and neor-specific RNA in the clones were proportional to the concentration of the vector injected. We have demonstrated that when the linearized plasmid was injected into the macronucleus, the prokaryotic sequence conferred an antibiotic resistance to Paramecium despite codon-usage differences.
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  • 6
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . Paramecium continues to be used to study motility, behavior, exocytosis, and the relationship between the germ and the somatic nuclei. Recent progress in molecular genetics is described. Toward cloning genes that correspond to mutant phenotypes, a method combining complementation with microinjected DNA and library sorting has been used successfully in cloning several novel genes crucial in membrane excitation and in trichocyst discharge. Paramecium transformation en masse has now been shown by using electroporation or bioballistics. Gene silencing has also been discovered in Paramecium, recently. Some 200 Paramecium genes, full length or partial, have already been cloned largely by homology. Generalizing the use of gene silencing and related reverse-genetic techniques would allow us to correlate these genes with their function in vivo.
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  • 7
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We examined both the somatic (macro-) and the germinal (micronuclear) DNAs that encode two K+-channel isoforms. PAK1 and PAK11, in Paramecium tetraurelia. The coding regions of these two isoforms are 88% identical in nucleotides and 95% identical in amino acids. Their introns are also highly conserved. Even some of the internal eliminated sequences in PAK1 and PAK11 are clearly related. PAK1 has five IESs; PAK11 has four. The first (5′-most) IESs of the two genes are located at the same site in the coding sequence but differ in size. The 2nd IES in PAK1 (206-bp), the largest among the nine IESs, has no PAK11 counterpart. The 3rd, 4th and 5th IESs in PAK1 have a counterpart in PAK11 that is similar in size and in sequence, and identical in its position in the coding sequence. In addition, the first IES of PAK11 bears some resemblance to the 4th one of PAK1. The similarities and differences between the two sets of IESs are discussed with respect to the origin and divergence of the two K+-channel isoforms.
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  • 8
    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.
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  • 9
    ISSN: 1432-1424
    Keywords: Paramecium ; patch clamp ; K channel ; Ca2+ dependence ; proteolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of proteolysis on a hyperpolarization- and Ca2+-dependent K channel from the surface membrane ofParamecium tetraurelia were examined in the inside-out excised patch mode. Treatment with trypsin, pronase or thermolysin removed the Ca2+-dependence of the channel activation, yielding an increase in channel activity greater than 2.5-fold at all Ca2+ concentrations between 10−4 and 10−8 m. Thermolysin addition-ally removed the voltage dependence of channel opening and gave the most activation among the three proteases tested. Proteolysis did not affect the single-channel conductance. In an analogy to the mechanism of activation of many Ca2+-dependent enzymes it is suggested that thisParamecium channel has a cytoplasmic inhibitory domain which can be removed by proteolysis, and that the physiological activation by Ca2+ is due to a temporary removal of this inhibition. Moreover, these findings indicate structural differences between depolarization-, Ca2+-dependent K channels (BK channels) and the hyperpolarization-, Ca2+-dependent K channels inParamecium.
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  • 10
    ISSN: 1432-1424
    Keywords: Paramecium ; patch clamp ; K channels ; Ca i 2+ -dependence ; hyperpolarization activated ; run-down
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have studied a class of Ca i 2+ -dependent K channels in inside-out excised membrane patches fromParamecium under patch clamp. Single channels had a conductance of 72 ±9.0 pS in a solution containing 100mM K+. The channels were selective for K+ over Rb+ with the permeability ratio of 1∶ 0.56. and over Na+, Cs+ or NH 4 + with a ratio 1∶〈0.1. The channel activity was dependent on Ca i 2+ , which was applied to the cytoplasmic side; the Ca i 2+ concentration for the half maximal activation was 2 μm. The Hill coefficient for the Ca i 2+ dependence of the channel activity was 2.58, indicating that more than two Ca i 2+ bindings are necessary for full activation. Unlike most Ca i 2+ -dependent K channels in other organisms, the channels inParamecium were slightly more active upon hyperpolarization than upon depolarization. The voltage dependence was fitted to a Boltzmann curve with 41.2 mV pere-fold change in channel activity. While a high Ca i 2+ concentration activated the channels, it also irreversibly reduced the channel activity over time. The decay of channel activity occurred faster at higher Ca i 2+ concentrations. Quaternary ammonium ions suppressed ion passage through the channel; more highly alkylated quaternary ammonium ions were more efficient in blocking. Ba i 2+ and Ca i 2+ were relatively ineffective in blockage. It was concluded that these Ca i 2+ -dependent K channels inParamecium are different from the previously described Ca i 2+ -dependent K channels, and are perhaps of a novel class.
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