We have analyzed the enzymatic activity of the sarcoplasmic reticulum (SR) Ca2+-transporting ATPase (SERCA) from the horse gluteal muscle. Horses are bred for peak athletic performance yet exhibit a high incidence of exertional rhabdomyolysis, with elevated levels of cytosolic Ca2+ proposed as a correlative linkage. We recently reported an improved protocol for isolating SR vesicles from horse muscle; these horse SR vesicles contain an abundant level of SERCA and only trace-levels of sarcolipin (SLN), the inhibitory peptide subunit of SERCA in mammalian fast-twitch skeletal muscle. Here, we report that the in vitro Ca2+ transport rate of horse SR vesicles is 2.3 ± 0.7-fold greater than rabbit SR vesicles, which express close to equimolar levels of SERCA and SLN. This suggests that horse myofibers exhibit an enhanced SR Ca2+ transport rate and increased luminal Ca2+ stores in vivo. Using the densitometry of Coomassie-stained SDS-PAGE gels, we determined that horse SR vesicles express an abundant level of the luminal SR Ca2+ storage protein calsequestrin (CASQ), with a CASQ-to-SERCA ratio about double that in rabbit SR vesicles. Thus, we propose that SR Ca2+ cycling in horse myofibers is enhanced by a reduced SLN inhibition of SERCA and by an abundant expression of CASQ. Together, these results suggest that horse muscle contractility and susceptibility to exertional rhabdomyolysis are promoted by enhanced SR Ca2+ uptake and luminal Ca2+ storage.
Bibliographical noteFunding Information:
Funding: This study was supported in part by a Morris Animal Foundation grant to S.J.V, J.M.A., and D.D.T. (grant number D16EQ-004). Morris Animal Foundation is the global leader in supporting science that advances animal health. This study was supported in part by National Institutes of Health grants to D.D.T. (grant numbers GM027906 and AG026160) and to D.D.T. and R.L.C. (HL139065). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This study was supported in part by an American Heart Association grant to Z.C. (grant number 18TPA34170284/Chen, Zhenhui/2018). The funding agencies had no role in study design, data collection, data analysis, manuscript preparation, or decision to publish.
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- Calcium regulation
- Comparative biochemistry
- Excitation–contraction coupling
- Exertional rhabdomyolysis
- Intraluminal protein
- Ion-motive ATPase
- Membrane vesicles
- Regulatory subunit
- Skeletal muscle
PubMed: MeSH publication types
- Journal Article