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Sarcoplasmic Reticulum Phospholipid Fatty Acid Composition and Sarcolipin Content in Rat Skeletal Muscle
Val Andrew Fajardo1, Eric Bombardier1, Khanh Tran1
1Department of Kinesiology, University of Waterloo, 200 University Ave. W., Waterloo, ON, N2L 3G1, Canada.
The Journal of Membrane Biology
|July 22, 2015
Summary
Higher docosahexaenoic acid (DHA) and unsaturation in sarcoplasmic reticulum (SR) membranes, along with sarcolipin, influence muscle SR Ca(2+) permeability, impacting metabolism and obesity.
Area of Science:
- Muscle Physiology
- Cellular Metabolism
- Molecular Biology
Background:
- Previous studies indicated higher sarcoplasmic reticulum (SR) Ca(2+) permeability in rat soleus muscle compared to gastrocnemius muscles.
- SR Ca(2+) permeability is crucial for muscle function and energy balance.
- Sarcolipin is known to influence SR Ca(2+) permeability.
Purpose of the Study:
- To investigate the role of SR membrane lipid composition, specifically docosahexaenoic acid (DHA) content and fatty acid unsaturation, in differential SR Ca(2+) permeability across rat muscles.
- To examine the contribution of sarcolipin levels to SR Ca(2+) permeability.
- To explore the implications of these factors on muscle metabolism and diet-induced obesity.
Main Methods:
- Analysis of SR membrane lipid composition, including DHA content and fatty acid unsaturation, from rat soleus, red gastrocnemius (RG), and white gastrocnemius (WG) muscles.
- Quantification of sarcolipin protein levels in the SR membranes of these muscles.
- Assessment of SR Ca(2+) permeability using ionophore ratios in both wild-type and sarcolipin-null mice.
Main Results:
- SR membranes from soleus muscle exhibited significantly higher DHA content (5.3%) compared to RG (4.2%) and WG (3.3%).
- Soleus muscle showed significantly greater total SR membrane unsaturation and a higher unsaturation index (UI) than RG and WG muscles.
- Sarcolipin protein was substantially more abundant in soleus (17-fold) than in RG, and absent in WG. However, differences in SR Ca(2+) permeability persisted in sarcolipin-null mice.
Conclusions:
- SR membrane docosahexaenoic acid (DHA) content and overall fatty acid unsaturation are key contributors to differential SR Ca(2+) permeability in rat muscles.
- Sarcolipin expression also plays a role, but does not fully account for the observed differences in Ca(2+) permeability.
- These findings suggest that SR membrane composition and sarcolipin influence muscle metabolism and may be implicated in diet-induced obesity.
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