Myosin-like aggregates in trypsin-treated smooth muscle cells

Area of Science:

• Cell Biology
• Muscle Physiology
• Biochemistry

Background:

• Smooth muscle myosin's molecular organization is crucial for muscle contraction.
• The role of trypsin in altering smooth muscle structure requires further investigation.
• Understanding myosin filament dynamics is key to elucidating muscle function.

Purpose of the Study:

• To investigate the effect of trypsin on smooth muscle cell structure, specifically myosin filament organization.
• To explore the potential conformational changes in smooth muscle myosin induced by trypsin.
• To examine the interaction between trypsin and smooth muscle proteins.

Main Methods:

• Excising and soaking toad small intestine segments in Ringer's solution with trypsin.
• Fixing specimens for electron microscopy at controlled pH.
• Analyzing thin sections of the tunica muscularis using electron microscopy.

Main Results:

• Smooth muscle cells showed varying degrees of damage, with some exhibiting aggregated thick filaments resembling myosin tactoids.
• These myosin aggregates measured 250-300 Å in diameter and 0.5-1.0 µm in length, with some showing 143 Å periodicity.
• Cells with aggregated myosin lacked dense bodies and had segregated thick and thin filaments.

Conclusions:

• Trypsin induces the aggregation of smooth muscle myosin, suggesting myosin exists in a disaggregated state in vivo.
• Trypsin may alter myosin conformation directly or indirectly by affecting other regulatory proteins.
• This aggregation process impacts the structural organization of smooth muscle cells.