Myosin transitions in chronic stimulation do not involve embryonic isozymes

Area of Science:

• Muscle physiology
• Skeletal muscle adaptation
• Myosin isozyme transitions

Background:

• Fast skeletal muscles can transition to slow types with chronic low-frequency stimulation.
• This transformation involves changes in myosin heavy and light chains.
• Developmental muscle isozyme shifts typically proceed from embryonic to neonatal, then to fast or slow types.

Purpose of the Study:

• To investigate whether chronic stimulation of adult fast muscle induces a direct fast-to-slow myosin isozyme shift.
• To determine if this transformation requires the reexpression of developmental isozymes before adult slow isozyme synthesis.

Main Methods:

• Adenosine triphosphatase (ATPase) histochemistry
• Pyrophosphate gel electrophoresis of native isozymes
• Peptide mapping of myosin heavy chains
• Immunoblotting for embryonic myosin heavy chain
• Solid-phase radioimmunoassay

Main Results:

• Chronic stimulation induced a transition from adult fast to adult slow myosin isozymes in the dog diaphragm.
• This fast-to-slow transition did not involve the reexpression of embryonic myosin isozymes.

Conclusions:

• Adult fast skeletal muscle can directly shift to a slow myosin isozyme profile under chronic stimulation.
• The developmental pathway of isozyme expression is not recapitulated during this adaptive transformation.