Sarcoplasmic Reticulum from Horse Gluteal Muscle Is Poised for Enhanced Calcium Transport

Joseph Autry,Zhenhui Chen,Samuel Carlson,Razvan Cornea,Stephanie Valberg,David Thomas,Bengt Svensson

doi:10.3390/vetsci8120289

Abstract

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.

Highlights

Introduction published maps and institutional affilHorses are highly susceptible to muscle exertional rhabdomyolysis from a variety of causes, including glycogen storage disorders, malignant hyperthermia, and abnormalities in cytosolic Ca2+ regulation [1]
We recently developed a new protocol for isolating sarcoplasmic reticulum (SR) vesicles from horse muscle with
Coomassie densitometry was used to determine that SR vesicles from the horse gluteal muscle express ~55% less (53 ± 7%, p = 0.005) of the relative content of sarcoplasmic reticulum (SR) Ca2+-transporting ATPase (SERCA) compared to rabbit SR (Figure 1, Table S2), this determination may be a slight overestimate, since horse SR vesicles probably contain a small amount of GP and/or additional proteins that co-migrate with SERCA

Summary

Introduction

Horses are highly susceptible to muscle exertional rhabdomyolysis from a variety of causes, including glycogen storage disorders, malignant hyperthermia, and abnormalities in cytosolic Ca2+ regulation [1]. The horse species has been bred selectively for thousands of years to achieve a remarkable athletic ability, in part conferred by a naturally high proportion (75–95%) of fast-twitch myofibers in the locomotor muscles that provide powerful contraction and rapid running [2]. Recurrent exertional rhabdomyolysis (RER) is one of the most common causes of poor performance and economic loss in Thoroughbred racehorses [3,4]. The molecular etiology of RER in Thoroughbred racehorses has been proposed to involve defects in excitation–contraction coupling, SR Ca2+ cycling, electron transport, and mitochondrial protein translation [1,5,6,7,8].

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