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Myosin light chain phosphorylation facilitates in vivo myosin filament reassembly after mechanical perturbation Qi, Dake
Abstract
It is generally believed that the myosin thick filaments in smooth muscle are structurally less stable than those in striated muscle. In vitro studies have shown that phosphorylation of the 20-kD myosin light chain (MLC) facilitates formation of the thick filaments from monomeric myosins in solution. It appears that the structural integrity of the thick filaments can be enhanced by phosphorylation of the MLC. It is however not known whether the transition from monomeric to filamentous myosin occurs in intact smooth muscle when the light chains are phosphorylated during muscle activation. The physiological significance of the thick filament lability and the role of MLC phosphorylation in modulating the filament integrity in intact smooth muscle are still being debated. It has been shown in our laboratory that mechanical strain is able to induce partial dissolution of unphosphorylated myosin thick filaments in intact smooth muscle; repolymerization of the thick filaments occurs when the muscle is subjected to cycles of contraction and relaxation. The objective of my thesis research is to determine whether MLC phosphorylation is required for repolymerization of the thick filaments after they have been partially disassembled by mechanical agitation. We used the conventional electron microscopy to quantify the cross-sectional density of myosin thick filaments in airway smooth muscle; partial dissolution of the thick filaments was induced by applying length oscillations to the muscle preparation; recovery of the thick filament density after oscillation was examined in the presence and absence of wortmannin, a potent inhibitor of myosin light chain kinase (MLCK). The results showed that isometric force production in airway smooth muscle was totally dependent on MLC phosphorylation. The inhibition of MLC phosphorylation alone did not cause disassembly of myosin filaments. The unphosphorylated thick filaments however partially dissolved when the muscle was subjected to oscillatory strains, as evidenced by a 25% decrease in the filament density. The post-oscillation filament density did not recover when wortmannin was present; it recovered to the pre-oscillation level when wortmannin was removed. Based on the above findings, we conclude that thick filament formation in vivo is MLC phosphorylation dependent.
Item Metadata
Title |
Myosin light chain phosphorylation facilitates in vivo myosin filament reassembly after mechanical perturbation
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2002
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Description |
It is generally believed that the myosin thick filaments in smooth muscle are
structurally less stable than those in striated muscle. In vitro studies have shown that
phosphorylation of the 20-kD myosin light chain (MLC) facilitates formation of the thick
filaments from monomeric myosins in solution. It appears that the structural integrity of
the thick filaments can be enhanced by phosphorylation of the MLC. It is however not
known whether the transition from monomeric to filamentous myosin occurs in intact
smooth muscle when the light chains are phosphorylated during muscle activation. The
physiological significance of the thick filament lability and the role of MLC
phosphorylation in modulating the filament integrity in intact smooth muscle are still
being debated. It has been shown in our laboratory that mechanical strain is able to
induce partial dissolution of unphosphorylated myosin thick filaments in intact smooth
muscle; repolymerization of the thick filaments occurs when the muscle is subjected to
cycles of contraction and relaxation. The objective of my thesis research is to determine
whether MLC phosphorylation is required for repolymerization of the thick filaments
after they have been partially disassembled by mechanical agitation.
We used the conventional electron microscopy to quantify the cross-sectional
density of myosin thick filaments in airway smooth muscle; partial dissolution of the
thick filaments was induced by applying length oscillations to the muscle preparation;
recovery of the thick filament density after oscillation was examined in the presence and
absence of wortmannin, a potent inhibitor of myosin light chain kinase (MLCK). The
results showed that isometric force production in airway smooth muscle was totally
dependent on MLC phosphorylation. The inhibition of MLC phosphorylation alone did
not cause disassembly of myosin filaments. The unphosphorylated thick filaments
however partially dissolved when the muscle was subjected to oscillatory strains, as
evidenced by a 25% decrease in the filament density. The post-oscillation filament
density did not recover when wortmannin was present; it recovered to the pre-oscillation
level when wortmannin was removed. Based on the above findings, we conclude that
thick filament formation in vivo is MLC phosphorylation dependent.
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Extent |
4937986 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-08-17
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0090329
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2002-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.