Advanced

Slow cycling of unphosphorylated myosin is inhibited by calponin, thus keeping smooth muscle relaxed

Malmqvist, Ulf LU ; Trybus, K M; Yagi, S; Carmichael, J and Fay, F S (1997) In Proceedings of the National Academy of Sciences 94(14). p.7655-7660
Abstract
A key unanswered question in smooth muscle biology is whether phosphorylation of the myosin regulatory light chain (RLC) is sufficient for regulation of contraction, or if thin-filament-based regulatory systems also contribute to this process. To address this issue, the endogenous RLC was extracted from single smooth muscle cells and replaced with either a thiophosphorylated RLC or a mutant RLC (T18A/S19A) that cannot be phosphorylated by myosin light chain kinase. The actin-binding protein calponin was also extracted. Following photolysis of caged ATP, cells without calponin that contained a nonphosphorylatable RLC shortened at 30% of the velocity and produced 65% of the isometric force of cells reconstituted with the thiophosphorylated... (More)
A key unanswered question in smooth muscle biology is whether phosphorylation of the myosin regulatory light chain (RLC) is sufficient for regulation of contraction, or if thin-filament-based regulatory systems also contribute to this process. To address this issue, the endogenous RLC was extracted from single smooth muscle cells and replaced with either a thiophosphorylated RLC or a mutant RLC (T18A/S19A) that cannot be phosphorylated by myosin light chain kinase. The actin-binding protein calponin was also extracted. Following photolysis of caged ATP, cells without calponin that contained a nonphosphorylatable RLC shortened at 30% of the velocity and produced 65% of the isometric force of cells reconstituted with the thiophosphorylated RLC. The contraction of cells reconstituted with nonphosphorylatable RLC was, however, specifically suppressed in cells that contained calponin. These results indicate that calponin is required to maintain cells in a relaxed state, and that in the absence of this inhibition, dephosphorylated cross-bridges can slowly cycle and generate force. These findings thus provide a possible framework for understanding the development of latch contraction, a widely studied but poorly understood feature of smooth muscle. (Less)
Please use this url to cite or link to this publication:
author
publishing date
type
Contribution to journal
publication status
published
subject
in
Proceedings of the National Academy of Sciences
volume
94
issue
14
pages
7655 - 7660
publisher
National Acad Sciences
external identifiers
  • pmid:9207148
  • scopus:0030832240
ISSN
1091-6490
language
English
LU publication?
no
id
403a0a58-ce93-48ab-9736-fb42720f9aae (old id 1112281)
alternative location
http://www.pnas.org/content/94/14/7655.full
date added to LUP
2008-07-21 17:04:23
date last changed
2017-07-30 03:35:15
@article{403a0a58-ce93-48ab-9736-fb42720f9aae,
  abstract     = {A key unanswered question in smooth muscle biology is whether phosphorylation of the myosin regulatory light chain (RLC) is sufficient for regulation of contraction, or if thin-filament-based regulatory systems also contribute to this process. To address this issue, the endogenous RLC was extracted from single smooth muscle cells and replaced with either a thiophosphorylated RLC or a mutant RLC (T18A/S19A) that cannot be phosphorylated by myosin light chain kinase. The actin-binding protein calponin was also extracted. Following photolysis of caged ATP, cells without calponin that contained a nonphosphorylatable RLC shortened at 30% of the velocity and produced 65% of the isometric force of cells reconstituted with the thiophosphorylated RLC. The contraction of cells reconstituted with nonphosphorylatable RLC was, however, specifically suppressed in cells that contained calponin. These results indicate that calponin is required to maintain cells in a relaxed state, and that in the absence of this inhibition, dephosphorylated cross-bridges can slowly cycle and generate force. These findings thus provide a possible framework for understanding the development of latch contraction, a widely studied but poorly understood feature of smooth muscle.},
  author       = {Malmqvist, Ulf and Trybus, K M and Yagi, S and Carmichael, J and Fay, F S},
  issn         = {1091-6490},
  language     = {eng},
  number       = {14},
  pages        = {7655--7660},
  publisher    = {National Acad Sciences},
  series       = {Proceedings of the National Academy of Sciences},
  title        = {Slow cycling of unphosphorylated myosin is inhibited by calponin, thus keeping smooth muscle relaxed},
  volume       = {94},
  year         = {1997},
}