Lactate dehydrogenase in human skeletal muscle

Area of Science:

• Exercise Physiology
• Biochemistry
• Muscle Biology

Background:

• Lactate dehydrogenase (LDH) is a key enzyme in energy metabolism.
• LDH exists as different isozymes, with varying tissue specificity.
• Understanding LDH activity and isozyme patterns in skeletal muscle is crucial for metabolic research.

Purpose of the Study:

• To investigate the relationship between LDH activity, skeletal muscle fiber type distribution, and environmental factors like training.
• To determine the role of LDH isozymes in human skeletal muscle metabolism.
• To explore the regulatory function of LDH in glycogenolysis during physical activity.

Main Methods:

• Analysis of total LDH activity and isozyme patterns in human skeletal muscle biopsies.
• Correlation of LDH parameters with slow-twitch (ST) or type I fiber percentages.
• Assessment of LDH changes following different training regimens (endurance and anaerobic).
• In vitro studies to evaluate product inhibition of LDH activity.
• Investigation of intracellular LDH isozyme distribution.

Main Results:

• A negative correlation was observed between total LDH activity and the percentage of ST/type I fibers.
• Elevated activity of heart-specific (H-LDH) isozymes was noted in ST fibers.
• Endurance training increased H-LDH relative activity, while extreme anaerobic training showed no significant changes.
• LDH activity exhibited strong product inhibition at physiological concentrations, suggesting a regulatory role in glycogenolysis.
• Muscle-specific LDH was localized to sarcoplasmic reticulum and outer mitochondrial membranes, while H-LDH was found in mitochondria.

Conclusions:

• LDH activity and isozyme composition in human skeletal muscle are influenced by fiber type and training status.
• LDH plays a regulatory role in muscle glycogenolysis.
• Specific LDH isozymes exhibit distinct intracellular localization patterns within muscle cells.