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  • 1
    Electronic Resource
    Electronic Resource
    Activation of the contractile system of insect fibrillar muscle at very low concentrations of Mg2+ and Ca2+ (1979)
    Springer
    Pflügers Archiv 382 (1979), S. 155-163 
    Details
    ISSN: 1432-2013
    Keywords: Crossbridges ; Ca2+-activation ; Magnesium ions ; Insect fibrillar muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The mechanical properties of single fibres and fibre bundles of glycerinated dorsal longitudinal muscle from lethocerus maximus were investigated in ATP-salt solutions containing only trace concentrations of free Ca2+ (pCa〉9). A reduction in the magnesium concentration (pMg ∼ 7) resulted in an increase in the instantaneous stiffness of glycerinated insect flight muscle fibres, though very little accompanying tension was developed. Stiffness was measured either using small amplitude sinusoidal length changes of high frequency (1 kHz) or rapid rectangular form length changes. The ratio of stiffness to tension in solutions free of added magnesium and calcium was equal to or greater than that obtained from the tissue in the rigor state, and much larger than that obtained in the presence of both magnesium and calcium. Extrapolation of the linear part of the change-tension relationship (obtained during rapid length changes completed within 0.3 ms) back to zero tension indicated that the elastic elements of attached crossbridges were less extended under conditions of Mg2+-deprivation than during Ca-activation in Mg2+-rich solution. Following a quick stretch a delayed tension development similar to that obtained in the presence of magnesium and calcium ions was observed. The rise in tension was delayed with respect to the accompanying rise in stiffness and reached a peak value after about 2 s. Similar tension transients followed a subsequent release. The possibility that an unusually slow corss-bridge cycle might be responsible for these slow transients was suggested by the finding that the fibres showed a very low ATPase activity under these conditions which could be slightly activated by stretches. On increasing the free Ca2+ concentration during magnesium deprivation, the time course of the stretch induced tension transients became faster, while stiffness and the steady state tension rose to reach a ‘high tension state’ at aboutpCa 6.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584217
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclic AMP inhibits contractility of detergent treated glycerol extracted cardiac muscle (1981)
    Springer
    Pflügers Archiv 391 (1981), S. 208-212 
    Details
    ISSN: 1432-2013
    Keywords: Myocardial contractility ; Troponin phosphorylation ; c-AMP ; Calcium ions ; Myocardial skinned fibres
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Glycerinated myocardial fibres treated with a detergent (Lubrol WX) and suspended in ATP salt solution produce half maximum isometric tension at pCa 6.2 (at pH 6.7). After addition of cyclic AMP (1–100 μM), the pCa required for half maximum activation is 5.9. c-AMP in concentrations of 1–100 μM induces a dose dependent inhibition (up to 40$ at pCa 6), and this effect can be amplified by the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine) 10−4 M. The effect is similar in presence and absence of sodium fluoride 10 mM. Since in detergent treated skinned fibres the cell membrane and the sarcoplasmic reticulum are extracted and since the Ca2+ ion concentration was kept constant and buffered, we propose that c-AMP does not act via the cell membrane or the sarcoplasmic reticulum, but via phosphorylation of troponin I. The latter is the only component which becomes phosphorylated in skinned fibres during c-AMP induced relaxation, an effect which is also responsible for the inhibition of actomyosin ATPase at constant Ca2+ ion concentration (cf. Ray and England 1976).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00596172
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  • 3
    Electronic Resource
    Electronic Resource
    Inhibition of TnI-TnC interaction and contraction of skinned muscle fibres by the synthetic peptide TnI [104–115] (1989)
    Springer
    Pflügers Archiv 414 (1989), S. 430-436 
    Details
    ISSN: 1432-2013
    Keywords: Contractile activation ; Skinned muscle fibres ; Calcium ions ; Peptides ; Troponin-I
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Circular dichroism was used to study the induction of helix in TnC or TnI-TnC by the TnI peptide [104–115] at various Ca2+ concentrations. The increase in negative ellipticity and pCa2+ values for the peptide-TnC complex, indicates that binding of the peptide to TnC, induces a small helical conformational change in TnC. This results in an increase in the Ca2+ binding constant and the pCa50 value required to induce 50% of Ca2+-dependent helix in TnC. The introduction of the peptide to a preformed mixture of TnI-TnC resulted in an increase in negative ellipticity and a decrease in the pCa50 and the apparent Ca2+ binding constant towards the values obtained for the TnI peptide-TnC complex and away from those of TnI-TnC. This demonstrates that the TnI peptide can successfully compete with TnI for TnC and thereby inhibit the TnI-TnC interaction. The addition of the TnI peptide to skinned rabbit psoas or porcine cardiac fibres resulted in the inhibition of the force development and a decrease in the pCa50 values required for 50% Ca2+ activation. The magnitude of the inhibition of tension development and the shift in the Ca2+ sensitivity for skinned cardiac muscle fibres was approximately half that observed with skeletal muscle fibres. In view of the CD findings, these skinned fibre results can be accounted for by the peptide inhibiting the TnI interaction with TnC. However, it is possible that the TnI peptide also has a direct inhibitory effect on TM-actin. Mastoparan, another TnC binding peptide, also inhibited the tension development in skinned skeletal and cardiac muscle fibres, but was much less efficient than the TnI peptide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585053
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of the temperature dependence of the cross bridge parameters for attachment, force generation and detachment as deduced from mechano-chemical studies in glycerinated single fibres from the dorsal longitudinal muscle of Lethocerus maximus (1979)
    Springer
    European biophysics journal 6 (1979), S. 1-29 
    Details
    ISSN: 1432-1017
    Keywords: Myofibrillar ATPase ; Mechano-chemistry of muscle ; Insect fibrillar muscle ; Muscular energetics ; Kinetics of actin-myosin interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract 1) A study is presented on the effect of temperature on the mechanochemical states involved in the cross bridge cycle of single glycerinated dorsal longitudinal fibres from Lethocerus. Contraction was induced by immersing the fibre in a MgATP-salt solution at Ca2+∼10 ΜM (pH 6.7). 2) Rising the temperature increases the rates of isometric tension generation following an increase in the [Ca2+] from 0.01 to 10 ΜM as well as the steady state levels of isometric tension and the rates of ATP splitting. 3) Tension transients following stretches of rise times 250 Μs and amplitudes up to 0.4% L i comprise at least four phases: an elastic phase the amplitude of which decreases by raising the temperature; a biphasic quick phase of tension decay with a mean Q 10=2; a delayed tension rise (Q 10∼5). 4) Tension transients following releases of fall time 250 Μs and amplitudes up to 0.3% L i also comprise four phases: an elastic phase comparable to that observed following stretches; a deactivation phase composed of a single exponential and a slow recovery phase. 5) The number of cross bridges attached to the actin at any moment is not changed during the elastic and quick recovery phase following a release as well as during the elastic and fast quick phase following a stretch. However, the number of attached cross bridges decreases during the deactivation phase. 6) The early phases of tension adjustment (T curves) which were recorded during the releases showed a marked dependence on temperature. The T curves fitted with high accuracy the Huxley and Simmons (1971) predictions of cross bridge rotation. 7) Analysis of the T curves in terms of the Huxley and Simmons (1971) model shows that a) the stiffness of a single cross bridge (D=1.2 104− N/m) obeys Hook's law; b) the number of myosin heads attached to actin (24% of the total number) is not altered during releases; c) rotation of myosin heads from a perpendicular to an acute angled position extends the elastic element of a cross bridge by 11 nm; d) at 25
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537592
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    Paper (German National Licenses)
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