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A myosin phosphatase modulates contractility in skinned smooth muscle
C Bialojan1, J C Rüegg, J DiSalvo
1II. Physiologisches Institut, Universität Heidelberg, Federal Republic of Germany.
Pflugers Archiv : European Journal of Physiology
|October 1, 1987
Summary
Polycation-modulable myosin phosphatase significantly reduces calcium sensitivity and contraction in smooth muscle. This reversible effect highlights the phosphatase
Area of Science:
- Muscle physiology
- Biochemistry
- Enzymology
Background:
- Actin-myosin interactions are crucial for smooth muscle contraction.
- Calcium ions (Ca2+) regulate these interactions.
- Myosin phosphatase plays a role in modulating muscle contractility.
Purpose of the Study:
- To investigate the effect of polycation-modulable (PCM-) myosin phosphatase on Ca2+-dependent actin-myosin interactions.
- To determine how PCM-phosphatase influences Ca2+ sensitivity and contraction in smooth muscle fibers.
Main Methods:
- Studied detergent-skinned smooth muscle fibers from chicken gizzard.
- Measured isometric contraction and Ca2+ concentration (A0.5).
- Utilized two-dimensional electrophoresis to assess myosin light chain phosphorylation.
Main Results:
- PCM-phosphatase increased the Ca2+ concentration required for half-maximal contraction (A0.5) by 2-fold.
- The enzyme decreased Ca2+-sensitivity for myosin light chain phosphorylation.
- Unloaded shortening velocity was reduced by 92% with PCM-phosphatase.
- Rapid relaxation was observed upon addition of PCM-phosphatase to contracted fibers.
Conclusions:
- PCM-phosphatase reversibly decreases Ca2+-sensitivity and force in smooth muscle.
- Both tension and shortening velocity are linked to light chain phosphorylation.
- Modulation of phosphatase activity may be a key mechanism in smooth muscle contractility control.