Myoplasmic calcium regulation in myotubes from horses with recurrent exertional rhabdomyolysis.

The study investigated if changes in the regulation of calcium in muscle cells could be identified in horses with recurrent exertional rhabdomyolysis (RER), a muscle disorder. The results revealed that muscle cells from RER-affected horses were more sensitive to caffeine, suggesting an alteration in muscle cell calcium management, which could be a primary cause for this inherited muscle disorder.

Background

• Recurrent exertional rhabdomyolysis (RER) is a muscle disease that frequently affects Thoroughbred horses. This disease leads to muscle breakdown and weakness, affecting the horse’s performance ability.
• The study intended to investigate the significance of myoplasmic calcium regulation, which plays a vital role in muscle contraction and relaxation, in the context of RER.
• This study used myotube cell cultures and intact muscle fibers from both normal and RER-affected Thoroughbreds to compare calcium responses.

Methods

• The researchers obtained muscle biopsy specimens from 6 affected and 8 normal Thoroughbred horses to create myotube cell cultures.
• They used Fura-2 fluorescence to measure resting calcium concentration within the muscle cells, and their response to caffeine and 4-chloro-m-cresol (4-CMC), both known to increase intracellular calcium levels.
• They prepared intact muscle fiber bundles from the same horse groups to assess their sensitivity to caffeine- and 4-CMC-induced contractions.

Results

• The resting calcium concentrations in myotubes from both RER-affected and control horses were identical.
• Upon exposure to caffeine, the intracellular calcium concentrations increased significantly in myotubes from RER-affected horses compared to control myotubes.
• There were no observable differences in the response of the myotubes from both horse groups to 4-CMC.
• The threshold for inducing contractions by caffeine was significantly lower in muscle bundles from RER-affected horses than the control group, but the threshold to 4-CMC was similar in both groups.

Conclusions

• The researchers concluded that muscle cells from a family of related RER-affected horses demonstrate increased sensitivity to caffeine, detected with calcium imaging and fiber bundle contractility techniques.
• This finding suggests that alterations in muscle cell calcium regulation could be a primary cause for RER, thus revealing a new potential area for diagnosing and managing this muscle disorder.