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  • 1
    Electronic Resource
    Electronic Resource
    Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1002-1006 
    Details
    ISSN: 1420-9071
    Keywords: Smooth muscle ; calcium ; myosin light chain kinase ; regulation of contraction ; ATPase ; mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The contraction induced by a Ca2+-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (Fo), immediate elastic recoil (SE), unloaded shortening velocity (Vus), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca2+-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. Fo developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. Vus in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than Vus induced by Ca2+ (1.6x10−6M) in the control fibers. Addition of Ca2+ (1.6x10−6M) to a contraction induced by MLCK-resulted in small increases in both Fo and Vus. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca2+. We conclude that with respect to actin-myosin interaction, MLCK- and Ca2+-induced contractions are similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952121
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of Ca2+-independent myosin light chain kinase on different skinned smooth muscle fibers (1984)
    Springer
    Pflügers Archiv 401 (1984), S. 107-109 
    Details
    ISSN: 1432-2013
    Keywords: Smooth muscle ; Skinned fibers ; Ca2+ ; Myosin light chain kinase ; Contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In various skinned smooth muscle fiber preparations, (porcine carotid artery, rat tail artery, chicken gizzard and Taenia coli from guinea pig) a Ca2+-independent myosin light chain kinase (MLCK) initiated a contraction in absence of Ca2+. While the Ca2+ insensitive MLCK was effective on the vertebrate smooth muscles it did not act on the invertebrate skinned skeletal muscle preparation from Limulus and anterior byssus retractor muscle from Mytilus edulis. The results indicate that in vertebrate smooth muscles phosphorylation is sufficient for activation and that there is no obligatory role for an additional mechanism in initiation of contraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581542
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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
    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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  • 5
    Electronic Resource
    Electronic Resource
    Temporal relationship between force, ATPase activity, and myosin phosphorylation during a contraction/relaxation cycle in a skinned smooth muscle (1990)
    Springer
    Pflügers Archiv 416 (1990), S. 512-518 
    Details
    ISSN: 1432-2013
    Keywords: Smooth muscle ; Contractile proteins ; Myosin phosphorylation ; Skinned fibres ; ATPase activity ; Smooth muscle regulation ; Calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The temporal relationship between myosin phosphorylation, contractile force and ATPase activity was studied in skinned preparations from the guinea-pig Taenia coli. When free Calcium concentration ([Ca2+]) was increased from pCa (−log[Ca2+]) 9 to pCa 4.5 at low calmodulin concentration (0.05 μM), ATPase activity and myosin light-chain phosphorylation rose quickly, while the increase in force and stiffness was delayed. The time-course of tension increase was faster at higher calmodulin concentrations (5 μM), although the maximal level of phosphorylation was unchanged. Lowering the calcium concentration from pCa 4.5 to pCa 9 at the plateau of contraction caused a rapid decrease in ATPase activity and in myosin phosphorylation, while force and stiffness decayed more slowly. The force decay could be accelerated by inorganic phosphate. These results suggest that, during contraction, force may be produced actively by phosphorylated and ATP-splitting cross-bridges, but may be maintained by dephosphorylated cross-bridges which cycle slowly. However, force could also be modulated by calmodulin and inorganic phosphate in a manner not involving an alteration in the extent of myosin phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382683
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  • 6
    Electronic Resource
    Electronic Resource
    Relaxation of skinned coronary arteries depends on the relative concentrations of Ca2+, calmodulin and active cAMP-dependent protein kinase (1985)
    Springer
    Pflügers Archiv 405 (1985), S. 70-76 
    Details
    ISSN: 1432-2013
    Keywords: Skinned coronary arteries ; Smooth muscle ; Regulation of contractile tone ; cAMP-dependent protein kinase ; cAMP-dependent modulation of contractile tone ; Calmodulin ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Maximally contracted detergent skinned coronary smooth muscle fibres are relaxed by lowering the concentration of free Ca2+. The extent and rate of relaxation depends on the concentration of free Ca2+ and calmodulin (CaM) suggesting that it is the Ca2+. CaM complex which is responsible for maintaining tension. At a fixed concentration of Ca2+ and CaM further relaxation can be achieved by addition of the catalytic subunit of the cAMP-dependent protein kinase (cAMP-kinase). The extent as well as the relaxation rate depend on the concentration of cAMP-kinase (0.01–0.5 μM) and both are antagonized by high concentrations of Ca2+ and CaM. The Ca2+-requirement for obtaining half maximal concentration is shifted from 1.1 μM to 6.3 μM Ca2+ in the presence of 0.5 μM cAMP-kinase. These data indicate that the response of the contractile apparatus to a change in the free [Ca2+] can be modulated by cAMP-kinase at the level of the contractile proteins. It is further suggested that the tone of coronary smooth muscle is determined by the relative and not by the absolute concentrations of Ca2+, CaM and cAMP-kinase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00591100
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  • 7
    Electronic Resource
    Electronic Resource
    Skinned smooth muscle: calcium-calmodulin activation independent of myosin phosphorylation (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 569-571 
    Details
    ISSN: 1432-2013
    Keywords: Smooth muscle ; Skinned fibers ; Calmodulin ; Myosin phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In chemically skinned chicken gizzard smooth muscle fibers investigated shortly after preparation, a contraction may be induced by calcium and calmodulin which is independent of myosin phosphorylation at intermediate Ca2+-concentrations. However, fibers stored for a prolonged period also contract in the absence of exogenous calmodulin and exhibit a close relationship between force development and myosin phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657520
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