A calcineurin-like phosphatase is required for catch contraction

Area of Science:

• Muscle physiology
• Biochemistry
• Molluscan biology

Background:

• Certain molluscan smooth muscles exhibit a unique 'catch' state, maintaining prolonged contraction.
• This 'catch' phenomenon has been linked to the activity of a calcium (Ca2+)-regulated phosphatase.
• The specific phosphatase involved, however, remained to be fully elucidated.

Purpose of the Study:

• To investigate the role of a calcineurin-like phosphatase in the 'catch' state of molluscan smooth muscle.
• To determine if this phosphatase is essential for maintaining tension during prolonged contraction.

Main Methods:

• Western blot analysis to detect the phosphatase.
• Calmodulin-binding overlay assay to assess phosphatase activity.
• Detergent treatment of muscle fibers to release the phosphatase.
• Perfusion experiments with calcineurin to reverse observed effects.

Main Results:

• Extensive detergent treatment of muscle fibers released the calcineurin-like phosphatase.
• This release led to a loss of the 'catch' tension maintenance.
• Re-introducing calcineurin restored the muscle's ability to maintain catch tension.

Conclusions:

• The activity of a calcineurin-like Ca(2+)-regulated phosphatase is critical for maintaining 'catch' in molluscan smooth muscle.
• This phosphatase is likely activated during the onset of contraction and plays a key role in sustaining tension.
• These findings provide molecular insight into the mechanism of muscle 'catch'.