Oleate oxidation and mitochondrial substrate selection in vascular smooth muscle

Area of Science:

• Mitochondrial metabolism
• Vascular smooth muscle physiology
• Nutrient substrate utilization

Background:

• Vascular smooth muscle (VSM) cells rely on mitochondrial substrate oxidation for energy.
• The relative contribution of different substrates, particularly long-chain fatty acids, to VSM energy production remains incompletely understood.

Purpose of the Study:

• To quantify the contribution of exogenous long-chain fatty acids (LCFAs) to overall substrate oxidation in VSM.
• To compare LCFA oxidation with that of other key mitochondrial substrates like glucose and acetate.

Main Methods:

• Hog carotid arteries were incubated with labeled substrates: oleic acid, glucose, and acetate.
• Substrate oxidation was measured using 13C-isotopomer analysis of glutamate.
• Experiments were conducted with and without carnitine to assess its effect on LCFA oxidation.

Main Results:

• Exogenous oleic acid (a LCFA) contributed approximately 5% to total substrate oxidation in VSM.
• Carnitine slightly increased LCFA oxidation to ~8% and reduced endogenous lipid oxidation.
• Glucose and acetate oxidation remained largely unaffected by the presence of oleic acid.

Conclusions:

• Long-chain fatty acids are minor contributors to energy metabolism in vascular smooth muscle.
• Glucose and acetate are the predominant mitochondrial substrates, accounting for approximately 80% of oxidation in VSM.
• These findings highlight the importance of glucose and acetate in maintaining VSM function.