Myoplasmic calcium regulation in myotubes from horses with recurrent exertional rhabdomyolysis

• Published in: American journal of veterinary research Vol. 63; no. 12; pp. 1724 - 1731
• Main Authors: Lentz, Linnea R, Valberg, Stephanie J, Herold, Lee V, Onan, Gary W, Mickelson, James R, Gallant, Esther M
• Format: Journal Article
• Language: English
• Published: United States 01.12.2002
• Subjects: Animals; biopsy; Biopsy - veterinary; caffeine; Caffeine - pharmacology; calcium; Calcium - metabolism; cell culture; Central Nervous System Stimulants - pharmacology; contracture; Cresols - pharmacology; crossbreds; Female; fluorescence; Fluorescent Dyes - chemistry; Fura-2 - chemistry; Horse Diseases - metabolism; Horse Diseases - physiopathology; Horses; image analysis; In Vitro Techniques; Male; Membrane Potentials - physiology; Microscopy, Fluorescence - veterinary; Muscle Contraction - physiology; muscle fibers; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - metabolism; muscles; myocytes; Physical Exertion; rhabdomyolysis; Rhabdomyolysis - genetics; Rhabdomyolysis - physiopathology; Rhabdomyolysis - veterinary; Thoroughbred
• ISSN: 0002-9645; 1943-5681
• DOI: 10.2460/ajvr.2002.63.1724

Objective-To determine whether alterations in myoplasmic calcium regulation can be identified in muscle cell cultures (myotubes) and intact muscle fiber bundles derived from Thoroughbreds affected with recurrent exertional rhabdomyolysis (RER). Animals-6 related Thoroughbreds with RER and 8 clinically normal (control) Thoroughbred or crossbred horses. Procedures-Myotube cell cultures were grown from satellite cells obtained from muscle biopsy specimens of RER-affected and control horses. Fura-2 fluorescence was used to measure resting myoplasmic calcium concentration as well as caffeine- and 4-chloro-m-cresol (4-CMC)-induced increases in myoplasmic calcium. In addition, intact intercostal muscle fiber bundles were prepared from both types of horses, and their sensitivities to caffeine- and 4-CMC-induced contractures were determined. Results-Myotubes of RER-affected and control horses had identical resting myoplasmic calcium concentrations. Myotubes from RER-affected horses had significantly higher myoplasmic calcium concentrations than myotubes from control horses following the addition of ≥ 2mM caffeine; however, there was no difference in their response to 4-CMC (greater than 1mM). Caffeine contracture thresholds for RER and control intact muscle cell bundles (2 vs 10mM, respectively) were significantly different, but 4-CMC contracture thresholds of muscle bundles from RER-affected and control horses (500µM) did not differ. Conclusions and Clinical Relevance-An increase in caffeine sensitivity of muscle cells derived from a family of related RER-affected horses was detected in vitro by use of cell culture with calcium imaging and by use of fiber bundle contractility techniques. An alteration in muscle cell calcium regulation is a primary factor in the cause of this heritable myopathy.