title: Functional characterization of orbicularis oculi and extraocular muscles.
abstract: The orbicularis oculi are the sphincter muscles of the eyelids and are involved in modulating facial expression. They differ from both limb and extraocular muscles (EOMs) in their histology and biochemistry. Weakness of the orbicularis oculi muscles is a feature of neuromuscular disorders affecting the neuromuscular junction, and weakness of facial muscles and ptosis have also been described in patients with mutations in the ryanodine receptor gene. Here, we investigate human orbicularis oculi muscles and find that they are functionally more similar to quadriceps than to EOMs in terms of excitation-contraction coupling components. In particular, they do not express the cardiac isoform of the dihydropyridine receptor, which we find to be highly expressed in EOMs where it is likely responsible for the large depolarization-induced calcium influx. We further show that human orbicularis oculi and EOMs express high levels of utrophin and low levels of dystrophin, whereas quadriceps express dystrophin and low levels of utrophin. The results of this study highlight the notion that myotubes obtained by explanting satellite cells from different muscles are not functionally identical and retain the physiological characteristics of their muscle of origin. Furthermore, our results indicate that sparing of facial and EOMs in patients with Duchenne muscular dystrophy is the result of the higher levels of utrophin expression.
authors.affiliation: Department of Anesthesia, Basel University Hospital, 4031 Basel, Switzerland Department of Biomedicine, Basel University Hospital, 4031 Basel, Switzerland.
authors.forename: Marijana
authors.initials: M
authors.lastname: Sekulic-Jablanovic
authors.affiliation: Institute of Physiology and Pathophysiology, Department of Cardiovascular Physiology, University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Nina D
authors.initials: ND
authors.lastname: Ullrich
authors.affiliation: Eye Clinic, Basel University and Basel University Hospital, 4031 Basel, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Goldblum
authors.affiliation: Eye Clinic, Basel University and Basel University Hospital, 4031 Basel, Switzerland.
authors.forename: Anja
authors.initials: A
authors.lastname: Palmowski-Wolfe
authors.affiliation: Department of Anesthesia, Basel University Hospital, 4031 Basel, Switzerland Department of Biomedicine, Basel University Hospital, 4031 Basel, Switzerland Department of Life Sciences and Biotechnology, General Pathology Section, University of Ferrara, 44100 Ferrara, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Zorzato
authors.affiliation: Department of Anesthesia, Basel University Hospital, 4031 Basel, Switzerland Department of Biomedicine, Basel University Hospital, 4031 Basel, Switzerland Department of Life Sciences and Biotechnology, General Pathology Section, University of Ferrara, 44100 Ferrara, Italy susan.treves@unibas.ch.
authors.forename: Susan
authors.initials: S
authors.lastname: Treves
mesh_terms: D000293:Adolescent; D000328:Adult; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D016189:Dystrophin / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009801:Oculomotor Muscles / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000378:metabolism; D049411:Utrophin / Q000235:genetics / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D016189:Dystrophin; D020033:Protein Isoforms; D049411:Utrophin