Characterization of excitation-contraction coupling components in human extraocular muscles.
Excitation-contraction coupling (ECC) is the physiological mechanism whereby an electrical signal detected by the dihydropyridine receptor, is converted into an increase in [Ca2+], via activation of ryanodine receptors (RyRs). Mutations in RYR1, the gene encoding RyR1, are the underlying cause of various congenital myopathies including central core disease, multiminicore disease (MmD), some forms of centronuclear myopathy (CNM) and congenital fibre-type disproportion. Interestingly, patients with recessive, but not dominant, RYR1 mutations show a significant reduction in RyR protein in muscle biopsies as well as ophthalmoplegia. This specific involvement of the extraocular muscles (EOMs) indicates that this group of muscles may express different amounts of proteins involved in ECC compared with limb muscles. In the present paper, we report that this is indeed the case; in particular the transcripts encoding RyR3, cardiac calsequestrin (CSQ2) and the α1 subunit of the cardiac dihydropyridine receptor are up-regulated by at least 100-fold, whereas excitation-coupled Ca2+ entry is 3-fold higher. These findings support the hypothesis that EOMs have a unique mode of calcium handling.
*Departments of Anesthesia and Biomedizin, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.
Marijana
M
Sekulic-Jablanovic
†Eye Hospital, Basel University Hospital, Mittlere Strasse 91, 4031Basel, Switzerland.
Anja
A
Palmowski-Wolfe
*Departments of Anesthesia and Biomedizin, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.
Francesco
F
Zorzato
*Departments of Anesthesia and Biomedizin, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.
Susan
S
Treves
D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling; D002155:Calsequestrin / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D056966:Excitation Contraction Coupling / Q000502:physiology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D032342:Muscle Cells / Q000166:cytology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D009154:Mutation; D009915:Orbit; D061251:Primary Cell Culture; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
C443109:CASQ2 protein, human; D020746:Calcium Channels, L-Type; D002155:Calsequestrin; D021122:Protein Subunits; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium