Effect of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum Ca-ATPase, on skeletal muscles from normal and mdx mice.
OBJECTIVE
In this study, we investigated Ca2+ loading by the sarcoplasmic reticulum in skeletal muscle from mdx mice, an animal model of human Duchenne's muscular dystrophy, at two stages of development: 4 and 11 weeks.


METHODS
Experiments were conducted on fast- (extensor digitorum longus, EDL) and slow- (soleus) twitch muscles expressing different isoforms of Ca2+-ATPase, which is responsible for the uptake of Ca2+ by the sarcoplasmic reticulum.


RESULTS
In sarcoplasmic reticulum vesicles, the ATP-dependent activity and sensitivity to cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum Ca2+-ATPase, were similar in mdx and normal EDL muscle. Furthermore, in chemically-skinned fibres from both normal and mdx muscles, the presence of CPA induced a decrease in Ca2+ uptake by the sarcoplasmic reticulum. However, the sensitivity to CPA was lower in mdx EDL muscle than in normal muscle. In addition, in EDL muscle from 4-week-old mdx mice, the expression of the slow Ca2+-pump isoform (SERCA2a) was significantly increased, without any accompanying change in slow myosin expression. In contrast, the expression and function of the Ca2+-ATPase in mdx soleus muscles at 4- and 11-weeks of development did not differ from those in age-matched controls.


CONCLUSIONS
These findings show that in dystrophic muscle, where the Ca2+ homeostasis was perturbed, the Ca2+ handling by the sarcoplasmic reticulum was altered in fast-twitch muscle, and this was associated with the expression of the slow isoform of SERCA. In these muscles, reduced Ca2+ uptake could then contribute to an elevated concentration of Ca2+ in the cytosol, and also to Ca2+ depletion of the sarcoplasmic reticulum.
Divet
A
A
CNRS UMR 6204, Faculté des Sciences et des Techniques, Université de Nantes, Nantes, Cedex 03, France.
Lompré
A-M
AM
Huchet-Cadiou
C
C
D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007150:Immunohistochemistry / Q000379:methods; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D018101:Mice, Inbred mdx; D009119:Muscle Contraction / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects*; D020388:Muscular Dystrophy, Duchenne / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D004791:Enzyme Inhibitors; D007211:Indoles; D009124:Muscle Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid