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Regulation of force and shortening velocity by calcium and myosin phosphorylation in chemically skinned smooth muscle

Malmqvist, Ulf LU and Arner, A (1996) In Pflügers Archiv 433(1-2). p.42-48
Abstract
The phosphatase inhibitor okadaic acid (OA) was used to study the relationship between [Ca2+], rates of phosphorylation/dephosphorylation and the mechanical properties of smooth muscle fibres. Force/velocity relationships were determined with the isotonic quick release technique in chemically skinned guinea-pig taenia coli muscles at 22 degrees C. In the maximally thiophosphorylated muscle neither OA (10 microM) nor Ca2+ (increase from pCa 9.0 to pCa 4.5) influenced the force-velocity relationship. When the degree of activation was altered by varying [Ca2+] in the presence of 0.5 microM calmodulin, both force and the maximal shortening velocity (Vmax) were altered. At pCa 5.75, at which force was about 35% of the maximal at pCa 4.5, Vmax... (More)
The phosphatase inhibitor okadaic acid (OA) was used to study the relationship between [Ca2+], rates of phosphorylation/dephosphorylation and the mechanical properties of smooth muscle fibres. Force/velocity relationships were determined with the isotonic quick release technique in chemically skinned guinea-pig taenia coli muscles at 22 degrees C. In the maximally thiophosphorylated muscle neither OA (10 microM) nor Ca2+ (increase from pCa 9.0 to pCa 4.5) influenced the force-velocity relationship. When the degree of activation was altered by varying [Ca2+] in the presence of 0.5 microM calmodulin, both force and the maximal shortening velocity (Vmax) were altered. At pCa 5.75, at which force was about 35% of the maximal at pCa 4.5, Vmax was 55% of the maximal value. When OA was introduced into fibres at pCa 6.0, force was increased from less than 5% to 100% of the maximal force obtained in pCa 4.5. The relationship between the degree of myosin light chain phosphorylation and force was similar in the two types of activation; varied [OA] at constant [Ca2+] and at varied [Ca2+]. The relation between force and Vmax when the degree of activation was altered with OA was almost identical to that obtained with varied [Ca2+]. The results show that Ca2+ and OA do not influence force or Vmax in the maximally phosphorylated state and suggest that the level of myosin light chain phosphorylation is the major factor determining Vmax. The finding that the relationship between force and Vmax was similar when activation was altered with OA and Ca2+ suggests, however, that alterations in the absolute rates of phosphorylation and dephosphorylation at a constant phosphorylation level do not influence the mechanical properties of the skinned smooth muscle fibres. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Okadaic acid, Myosin light chain phosphorylation, Skinned fibres, Force-velocity relation
in
Pflügers Archiv
volume
433
issue
1-2
pages
42 - 48
publisher
Springer
external identifiers
  • pmid:9019729
  • scopus:0029806862
ISSN
0031-6768
DOI
10.1007/s004240050246
language
English
LU publication?
yes
id
6f0245a0-22ea-460a-ab27-ada4be1c3ac6 (old id 1110907)
date added to LUP
2008-07-25 16:52:05
date last changed
2017-03-19 04:00:46
@article{6f0245a0-22ea-460a-ab27-ada4be1c3ac6,
  abstract     = {The phosphatase inhibitor okadaic acid (OA) was used to study the relationship between [Ca2+], rates of phosphorylation/dephosphorylation and the mechanical properties of smooth muscle fibres. Force/velocity relationships were determined with the isotonic quick release technique in chemically skinned guinea-pig taenia coli muscles at 22 degrees C. In the maximally thiophosphorylated muscle neither OA (10 microM) nor Ca2+ (increase from pCa 9.0 to pCa 4.5) influenced the force-velocity relationship. When the degree of activation was altered by varying [Ca2+] in the presence of 0.5 microM calmodulin, both force and the maximal shortening velocity (Vmax) were altered. At pCa 5.75, at which force was about 35% of the maximal at pCa 4.5, Vmax was 55% of the maximal value. When OA was introduced into fibres at pCa 6.0, force was increased from less than 5% to 100% of the maximal force obtained in pCa 4.5. The relationship between the degree of myosin light chain phosphorylation and force was similar in the two types of activation; varied [OA] at constant [Ca2+] and at varied [Ca2+]. The relation between force and Vmax when the degree of activation was altered with OA was almost identical to that obtained with varied [Ca2+]. The results show that Ca2+ and OA do not influence force or Vmax in the maximally phosphorylated state and suggest that the level of myosin light chain phosphorylation is the major factor determining Vmax. The finding that the relationship between force and Vmax was similar when activation was altered with OA and Ca2+ suggests, however, that alterations in the absolute rates of phosphorylation and dephosphorylation at a constant phosphorylation level do not influence the mechanical properties of the skinned smooth muscle fibres.},
  author       = {Malmqvist, Ulf and Arner, A},
  issn         = {0031-6768},
  keyword      = {Okadaic acid,Myosin light chain phosphorylation,Skinned fibres,Force-velocity relation},
  language     = {eng},
  number       = {1-2},
  pages        = {42--48},
  publisher    = {Springer},
  series       = {Pflügers Archiv},
  title        = {Regulation of force and shortening velocity by calcium and myosin phosphorylation in chemically skinned smooth muscle},
  url          = {http://dx.doi.org/10.1007/s004240050246},
  volume       = {433},
  year         = {1996},
}