Observations by electron microscopy on contraction of skeletal myofibrils induced with adenosinetriphosphate

Area of Science:

• Muscle physiology
• Cellular biology
• Biophysics

Background:

• Skeletal myofibrils are the fundamental contractile units of muscle.
• Understanding myofibril structure and function is crucial for muscle physiology research.
• Previous studies have described myofibril structure but lacked detailed contractile dynamics.

Purpose of the Study:

• To investigate the structural changes in skeletal myofibrils during contraction.
• To correlate structural alterations with contractile activity at the ultrastructural level.
• To examine the effects of enzymatic treatment on myofibril structure and contractility.

Main Methods:

• Isolation of skeletal myofibrils using tryptic digestion or a colloid mill.
• Incubation of myofibrils in a buffer solution with adenosinetriphosphate (ATP) at sub-zero temperatures.
• Induction of contraction by raising the temperature above 0°C.
• Electron microscopy to examine myofibril ultrastructure at various stages of contraction.
• Formalin fixation to halt contraction for microscopic analysis.

Main Results:

• Isolated myofibrils exhibited slow, progressive contraction upon warming above 0°C.
• Trypsin treatment removed Z bands and disorganized I bands, but did not abolish contraction.
• Electron microscopy revealed migration of dense material from A bands, increased fibril width, and decreased sarcomere length during contraction.
• Filament diameter appeared to increase, and their parallel arrangement became disoriented.

Conclusions:

• Skeletal myofibril contraction involves significant ultrastructural rearrangements.
• The contractile mechanism is robust, as enzymatic disruption of certain structures (Z bands) did not prevent contraction.
• These findings provide detailed insights into the molecular and structural basis of muscle contraction.