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  • 1
    Electronic Resource
    Electronic Resource
    Effects of Ca2+ and other divalent cations on K+-evoked force production of slow muscle fibers from Rana esculenta and Rana pipiens (1992)
    Springer
    The journal of membrane biology 129 (1992), S. 211-220 
    Details
    ISSN: 1432-1424
    Keywords: slow muscle fibers ; K+ contractures ; divalent cations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Slow muscle fibers were dissected from cruralis muscles of Rana esculenta and Rana pipiens. Isometric contractures were evoked by application of K+-rich Ringer's containing Ca2+, Ni2+, Co2+, Mn2+ or Mg2+. High (7.2 mmol/liter) external Ca2+ concentration raised, 0 Ca2+ lowered the K+ threshold. Replacing Ca2+ by Ni2+ or Co2+ had an effect similar to that of high Ca2+ Ringer's. In Mg2+ Ringer's the K+ concentration-response curve was flattened. These effects were observed already after short exposure times in both species of slow fibers. When Ca2+ was removed for long periods of time the slow fibers of R. esculenta lost their contractile response to application of high K+ concentrations much more quickly than those of R. pipiens, while the response to caffeine (20 mmol/liter) was maintained. Upon readmission of Ca2+ contractile ability was quickly restored in the slow fibers of both R. esculenta and R. pipiens, but the effects of Ni2+ (or Co2+, Mn2+ and Mg2+) were much larger in R. esculenta than in R. pipiens slow fibers. It is concluded that divalent cations have two different sites of action in slow muscle fibers. K+ threshold seems to be affected through binding to sites at the membrane surface; these sites bind Ni2+ and Co2+ more firmly than Ca2+. The second site is presumably the voltage sensor in the transverse tubular membrane, which controls force production, and where Ca2+ is the most effective species of the divalent cations examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00219516
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  • 2
    Electronic Resource
    Electronic Resource
    Competitive action of divalent cations and D600 in frog slow muscle fibers (1989)
    Springer
    The journal of membrane biology 112 (1989), S. 185-192 
    Details
    ISSN: 1432-1424
    Keywords: slow fiber ; K contracture ; D600 ; divalent cations ; competitive binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Single, slow muscle fibers fromRana temporaria were equilibrated in normal Ringer's. 95 mmol/liter K1-solution containing various concentrations of Ca2+, Ni2+, Mn2 or Mg2+ was applied, and the ensuing contractures were recorded isometrically. While peak tension (F max) was little affected, maintained tension (measured 1 min after onset of contracture) strongly depended on the concentration and species of divalent cations. Tension was maintained at its peak value in the presence of all species of divalent cations provided their concentrations were adequately increased. Dose-response curves were hyperbolic: Lineweaver-Burk plots revealed straight lines with different slopes intersecting near 1/F max, and indicating the following order of efficiency: Ni2+〉Ca2+〉Mn2+〉〉Mg2+. Hill plots for these cations resulted in straight lines with slopes near 1. Qualitatively similar relationships were obtained with contracture solutions containing D6000 (3–12 μmol/liter). However, under these conditions higher concentrations of Ca2+ or Ni2+ were required in order to fully maintain tension. After a step concentration change in the medium during contracture, the effects of Ca2+ or D600 were detectable only after a delay of 9 and 18 sec, respectively. It is concluded that divalent cations and D600 compete for the same binding site according to a 1:1 reaction. This site is presumably located inside the transverse tubular system and controls inactivation of the contractile force.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871279
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  • 3
    Electronic Resource
    Electronic Resource
    Dual effects of calcium on ATP-sensitive potassium channels of frog skeletal muscle
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1108 (1992), S. 119-122 
    Details
    ISSN: 0005-2736
    Keywords: (Frog) ; ATP binding ; Calcium ion dependence ; Potassium ion channel ; Skeletal muscle
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0005-2736(92)90122-3
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of D600 on potassium contractures of slow muscle fibres ofRana temporaria (1988)
    Springer
    Pflügers Archiv 412 (1988), S. 390-396 
    Details
    ISSN: 1432-2013
    Keywords: Slow fibre ; K-Contracture ; D600 ; Inactivation ; Repriming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract (1) The effect of 30 μM D600 on the amplitude and time course of isometric contractures was studied in single slow fibres ofRana temporaria. (2) D600 only slightly reduced the amplitude of contractures evoked with 30 or 95 mM K-Ringer's. Maintenance of tension was strongly impaired by D600 only during exposure to 95 mM K. The caffeine contracture was not affected. (3) Addition of 10 mM Ca2+ or other divalent cations to the medium strongly counteracted the effect of D600 on maintained tension. The order of efficiency was Ca2+=Ni2+〉Co2+〉Mn2+〉Mg2+. (4) During 2 min exposure to 95 mM K-Ringer's the slow fibres inactivated to a variable degree; recovery from inactivation in normal Ringer's proceeded with a half time of the order of 1 min, while in the presence of D600 recovery was prolonged 3.3 to 27 times. (5) It is concluded that the effect of D600 on the contractile behaviour of slow fibres fromRana temporaria is predominantly due to a prolongation of the inactivated state. It is suggested that D600 binds to a site at the outer membrane surface which also binds divalent cations and determines the degree of contractile inactivation during exposure to potassium. Blocking of Ca2+ channels is unlikely to be the mechanism of this D600-effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01907557
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    Paper (German National Licenses)
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