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  • 1
    Electronic Resource
    Electronic Resource
    Changes of Chloride Channel Regulation in Rat Skeletal Muscle during Aging (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 673 (1992), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1992.tb27447.x
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  • 2
    Electronic Resource
    Electronic Resource
    Cysteine Restores the Activity of ATP-Sensitive Potassium Channels of Skeletal Muscle Fibers of Aged Rats (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 717 (1994), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1994.tb12094.x
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  • 3
    Electronic Resource
    Electronic Resource
    Stereoselective interaction of tocainide and its chiral analogs with the sodium channels in human myoballs (1991)
    Springer
    Pflügers Archiv 418 (1991), S. 234-237 
    Details
    ISSN: 1432-2013
    Keywords: Antiarrhythmic drugs ; Sodium channels ; Molecular modelling ; Human muscle ; Whole-cell recording
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of both enantiomers of tocainide and of some of its chiral analogs on the inactivation of the sodium current in human myoballs were investigated with the whole-cell recording technique. Structure and electron densities of the applied compounds were calculated and compared to the results. Both the R(−) and the S(+) enantiomers had little effect on fast inactivation determined with short prepulses according to Hodgkin and Huxley (1952; h ∞ curve). When the inactivating prepulses used in this pulse protocol were prolonged to 1024 ms, both tocainide enantiomers increased inactivation severely, suggesting that the drug binds to the channel when it is in the state of intermediate inactivation (Fakler et al. 1990). Tetrodotoxin-resistant “juvenile” sodium channels were more affected than tetrodotoxin-sensitive “adult” channels. The R form was four times as effective as the S form. The compound obtained by substitution of the methyl group on the chiral centre of tocainide with a benzyl group, although in the less potent S form, affected inactivation of the juvenile sodium channels much more than the potent (R)-tocainide. Two additional substitutions, performed on the aromatic ring of tocainide, gave a compound that was most potent in shifting the inactivation curves, but without any selectivity for juvenile or adult channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370521
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  • 4
    Electronic Resource
    Electronic Resource
    Modulation of rat skeletal muscle chloride channels by activators and inhibitors of protein kinase C (1991)
    Springer
    Pflügers Archiv 418 (1991), S. 500-503 
    Details
    ISSN: 1432-2013
    Keywords: Rat skeletal muscle ; Phorbol esters ; Staurosporine ; Protein kinase C ; Chloride channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The membrane electrical parameters and component conductances of rat extensor digitorum longus muscle fibres were studied in vitro at 30 °C with standard two microelectrode square pulse cable analysis in the presence of protein kinase C (PKC) activators and inhibitors. The PKC activator, 4-β-phorbol-12,13 dibutyrate (4-β-PDB), (2–90nM) blocked up to 67% chloride conductance (G Cl) in rat skeletal muscle fibres and induced myotonic hyperexcitability. The concentration necessary to produce a 50% block of the membrane G Cl was 23 nM. The “inactive” 4-α-phorbol-12,13 dibutyrate had no effect at 2 μM. The blocking effect of 4-β-PDB on G Cl was prevented by preincubation of the preparations with the PKC inhibitors, staurosporine (1–5 μM) and tetrahydropapaverolone (50–100 μM). The blocking effects on membrane G Cl of 4-β-PDB and its antagonism by the inhibitors used support the concept of the involvement of PKC in regulating Cl channels of mammalian skeletal muscle fibres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00497778
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  • 5
    Electronic Resource
    Electronic Resource
    Enantiomers of clofibric acid analogs have opposite actions on rat skeletal muscle chloride channels (1988)
    Springer
    Pflügers Archiv 413 (1988), S. 105-107 
    Details
    ISSN: 1432-2013
    Keywords: Chloride channel ; Rat ; Skeletal muscle ; Stereoisomers ; 2-(p-chloro-phenoxy) isobutyric acid ; Clofibric acid ; Myotonia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The S-(−) isomers of a series of clofibric acid analogs produced only a block of chloride conductance of rat skeletal muscle fibers with increasing concentrations until block was nearly complete. The R-(+) isomers, on the other hand, at low concentrations increased chloride conductance by as much as 9% to 39% and at higher concentrations decreased chloride conductance, but never by more than 27% of the control value. The actions of the enantiomeric pairs to either produce or inhibit myotonic excitability paralleled their ability to block or increase chloride conductance, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581238
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  • 6
    Electronic Resource
    Electronic Resource
    Changes of the biophysical properties of calcium-activated potassium channels of rat skeletal muscle fibres during aging (1997)
    Springer
    Pflügers Archiv 434 (1997), S. 822-829 
    Details
    ISSN: 1432-2013
    Keywords: Key words Skeletal muscle ; Aging ; Ca2+-activated K+ channel ; Patch clamp ; Charybdotoxin ; MgATP ; ATP[γ-S]
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In the present work, we have investigated the effects of the aging process on Ca2+-activated K+ channels (KCa2+) of rat skeletal muscle fibres. KCa2+ channels of adult (5–7 months old) and aged (24–26 months old) rats were surveyed by the patch-clamp technique. In aged rats, KCa2+ channels were routinely detected on the surface membrane of the fibres in both cell-attached and inside-out configurations. Conversely, in adult rat fibres, KCa2+ channels were rarely detected. In the cell-attached configuration, the open probability of the aged rat KCa2+ channel, measured in the range of potentials from –60 mV to +20 mV, was about 1.5–2 times higher than that of the adult one. The number of functional channels was abnormally increased by aging. An average of three channels per patch/area was counted in the inside-out patches of aged rat fibres, whereas no more than one open channel per patch/area was detected in the adult rat fibres. The frequency of finding channels in the patches also increased with aging, i.e. 11.5% and 30.1% in the adult and in the aged rat fibres, respectively. However, no significant change in the single-channel conductance has been observed with aging: it was 227 pS and 231 pS for adult and aged rat channels, respectively. In detached patches, both the adult and aged rat channels showed a similar voltage dependence of open probability and a similar sensitivity to Ca2+ ions. The aging process did not alter the response of the single channel to charybdotoxin, or its modulation by nucleotides, MgATP and adenosine 5’-O-(3-thiotriphosphate) (ATP[γ-S]). On the other hand, charybdotoxin reduced the abnormally high resting macroscopic K+ conductance of the aged rat fibres, recorded using the two-intracellular-microelectrode technique. These findings indicate that, in skeletal muscle, the activity of KCa2+ channels increases with advancing age.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050471
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  • 7
    Electronic Resource
    Electronic Resource
    Insulin modulation of ATP-sensitive K+ channel of rat skeletal muscle is impaired in the hypokalaemic state (1999)
    Springer
    Pflügers Archiv 437 (1999), S. 235-240 
    Details
    ISSN: 1432-2013
    Keywords: Key words Hypokalaemic periodic paralysis ; ATP-sensitive K+ channels ; Insulin ; Skeletal muscle ; Patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In the present work, we examined the effects of in vivo administration of insulin to rats made hypokalaemic by feeding a K+-free diet. The i.p. injection of insulin in the hypokalaemic rats provoked muscle paralysis within 3–5 h. Consistent with this observation, the skeletal muscle fibres of the paralysed rats were depolarized. In contrast, in the normokalaemic animals, insulin neither provoked paralysis nor produced significant fibre hyperpolarization. In the hypokalaemic rats, insulin almost completely abolished the sarcolemma adenosine triphosphate (ATP)-sensitive K+ currents without altering the sensitivity of the channels to ATP or glibenclamide. In contrast, in the normokalaemic rats, insulin enhanced ATP-sensitive K+ currents that became also resistant to ATP and glibenclamide. Our experiments indicate that the modulation of the sarcolemma ATP-sensitive K+ channels by insulin is impaired in the hypokalaemic state. This phenomenon appears to be related to the fibre depolarization and paralysis observed in the same animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050774
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  • 8
    Electronic Resource
    Electronic Resource
    Aging and chloride channel regulation in rat fast-twitch muscle fibres (1994)
    Springer
    Pflügers Archiv 427 (1994), S. 80-85 
    Details
    ISSN: 1432-2013
    Keywords: Rat skeletal muscle ; Aging ; Chloride channels ; Phorbol esters ; Protein kinases ; Cholera toxin ; G protein pathways ; Calcium ionophore A23187
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract By the use of pharmacological tools, we tested the hypothesis that age-related alterations in the regulatory pathways of chloride channels might contribute to the lowered chloride conductance (G Cl) found in skeletal muscle of aged rats. The restingG Cl of extensor digitorum longus (EDL) muscles from adult rats either young (3–4 months old) or aged (29 months old) was measured by means of computerized intracellular microelectrode recordings. In EDL muscle from 3 to 4-month-old rats, 4-β-phorbol 12,13-dibutyrate (4-β-PDB), a direct activator of protein kinase C (PKC), decreasedG Cl in a concentration-dependent manner. The same effect was exerted by cholera toxin. The effects of both the phorbol ester and cholera toxin were inhibited by staurosporine, thus indicating that either direct or indirect (via G protein) activation of PKC accounts for the decrease ofG Cl. An increase of cytosolic Ca2+ by the ionophore A23187 also significantly decreasedG Cl by 25%. In EDL muscles from aged rats, 4-β-PDB was 20-fold more potent in blockingG Cl than in muscles from younger controls, and the ionophore blockedG Cl by 40%. On the other hand, cholera toxin was ineffective. Our findings support the hypothesis that in fast-twitch muscle the regulation of chloride channels by PKC and Ca2+ is a target of the aging process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585945
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of taurine analogues on chloride channel conductance of rat skeletal muscle fibers: a structure-activity relationship investigation (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 349 (1994), S. 416-421 
    Details
    ISSN: 1432-1912
    Keywords: Key words: Skeletal muscle – Chloride channel conductance – Taurine binding site – Taurine analogues – Structure-activity relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. In rat skeletal muscle, taurine was proposed to interact with a low affinity binding site on sarcolemmal phospholipids near chloride channel, increasing chloride conductance (GCl). In an attempt to evaluate the structure-activity relationship between taurine and its binding site, a series of N-azacycloalkenyl analogues of taurine (A: N-(1′aza-cyclohepten-2′yl)-2-aminoethane sulfonic acid; B: N-(1′-aza-cyclopenten-2′-yl)-2-aminoethane sulfonic acid; C: N-(1′aza-cyclohepten-2′-yl)-3-aminopropane sulfonic acid; D: N-(1′aza-cyclopenten-2′-yl)-3-aminopropane sulfonic acid) have been synthetized and tested in vitro on rat extensor digitorum longus (EDL) muscle. In spite of the presence of a bulky and lipophilic 5 or 7 membered heterocycle linked to the taurine amino group, analogues A and B determined an increase of GCl, although less potently than taurine. Also 3-aminopropane sulfonic acid (homotaurine), tested in comparison, showed less activity in increasing GCl with respect to taurine, probably for the increased distance between charged groups. Taurine analogues C and D, which differ from compounds A and B for an additional methylene group, showed much lower activity in increasing GCl. It has been reported that guanidinoethane sulfonate (GES) displaces taurine from the low affinity site on sarcolemma by only 7%. This compound, characterized by lower charge density on the guanidinium cationic head, applied in vitro on EDL muscle, show reduced taurine-like activity in increasing GCl. Our results support the hypothesis that the effect of taurine on muscle GCl is due to a specific binding on a low affinity site on sarcolemma and that charge delocalization reduces the binding probability more than the substitution of the primary amino group or the increased distance between charged groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170889
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of taurine analogues on chloride channel conductance of rat skeletal muscle fibers: a structure-activity relationship investigation (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 349 (1994), S. 416-421 
    Details
    ISSN: 1432-1912
    Keywords: Skeletal muscle ; Chloride channel conductance ; Taurine binding site ; Taurine analogues ; Structure-activity relationship
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In rat skeletal muscle, taurine was proposed to interact with a low affinity binding site on sarcolemmal phospholipids near chloride channel, increasing chloride conductance (GCI). In an attempt to evaluate the structure-activity relationship between taurine and its binding site, a series of N-azacycloalkenyl analogues of taurine (A: N-(1′aza-cyclopenten-2′yl)-2-aminoethane sulfonic acid; B: N-(1′-aza-cyclopenten-2′-yl)-2-aminoethane sulfonic acid; C: N-(1′aza-cyclopenten-2′-yl)-3-amino-propane sulfonic acid; D: N-(1′aza-cyclopenten-2′-yl)-3-aminopropane sulfonic acid) have been synthetized and tested in vitro on rat extensor digitorum longus (EDL) muscle. In spite of the presence of a bulky and lipophilic 5 or 7 membered heterocycle linked to the taurine amino group, analogues A and B determined an increase of GCI, although less potently than taurine. Also 3-aminopropane sulfonic acid (homotaurine), tested in comparison, showed less activity in increasing GCI with respect to taurine, probably for the increased distance between charged groups. Taurine analogues C and D, which differ from compounds A and B for an additional methylene group, showed much lower activity in increasing GCI. It has been reported that guanidinoethane sulfonate (GES) displaces taurine from the low affinity site on sarcolemma by only 7%. This compound, characterized by lower charge density on the guanidinium cationic head, applied in vitro on EDL muscle, show reduced taurine-like activity in increasing GCl. Our results support the hypothesis that the effect of taurine on muscle GCI is due to a specific binding on a low affinity site on sarcolemma and that charge delocalization reduces the binding probability more than the substitution of the primary amino group or the increased distance between charged groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170889
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