Creatine kinase activity in rat skeletal muscle relates to myosin phenotype during development

Area of Science:

• Muscle Physiology
• Biochemistry
• Developmental Biology

Background:

• Creatine kinase (CK) plays a crucial role in maintaining intracellular energy supply in skeletal muscle through ATP buffering.
• Understanding the developmental expression of CK and its relationship with muscle fiber type is essential for comprehending muscle energetics.

Purpose of the Study:

• To investigate the postnatal expression patterns of CK activity and isoform phenotype in different rat skeletal muscles.
• To correlate developmental changes in CK activity with myosin heavy chain (MHC) phenotype, an indicator of contractile protein energetic demands.

Main Methods:

• Assessed CK activity and isoform phenotype across four distinct skeletal muscles (diaphragm, intercostal, external abdominal oblique, soleus) during postnatal development in rats.
• Correlated CK activity with MHC isoform composition, analyzing the ratio of adult to developmental MHC isoforms.
• Utilized stepwise regression analysis to identify specific MHC isoforms influencing CK activity variance.

Main Results:

• CK activity was low at birth and increased postnatally in all studied muscles, with the highest levels observed in adult intercostal and external abdominal oblique muscles.
• A strong correlation was found between CK activity and MHC phenotype (r2 = 0.93, p < 0.001).
• Type IIb MHC expression was the primary determinant, explaining 79% of the developmental variance in CK activity.

Conclusions:

• CK activity exhibits muscle-specific increases during postnatal development, closely linked to the energetic demands reflected by MHC isoform composition.
• The energy buffering role of CK is hypothesized to be most significant in muscles predominantly expressing the IIb MHC isoform.