A Proposed Mechanism for Enhanced Titin-Based Force during Ca2+-activation

When an active skeletal muscle sarcomere is stretched, it generates more force after the stretch is completed when compared to a contraction at the same corresponding length. This mechanical property of skeletal muscle defies explanation by any conventional mechanism of contraction. Surmounting evidence indicates that the explanation for enhanced force following active stretch may be provided by the titin protein in the sarcomere, which becomes stiffer during Ca2+-activation. This thesis explores the mechanisms by which titin force is enhanced in actively stretched sarcomeres. Known to stiffen in the presence of Ca2+, the first study quantifies the contribution of Ca2+ to enhanced titin force, showing that an alternative mechanism accounts for the majority of titin force enhancement. The mechanism is further investigated using chemical inhibition of cross-bridges which shows that titin force enhancement is initiated with the development of contractile force. The next set of studies increase support for an interdependence of titin force enhancement and contractile force, showing that titin force enhancement is essentially eliminated and contractile force is decreased in sarcomeres with muscular dystrophy with myositis (mdm), a genetic mutation affecting the titin protein. The final study seeks to determine whether mechanical deficiencies in titin force enhancement are observed in a less reduced, single fiber preparation. Mutant fibers generated comparable contractile force and total force following active stretch beyond filament overlap as control fibers. Titin force enhancement was abolished in some mutant fibers and measured in other mutant fibers suggesting that the mdm mutation differentially affects fibers (and titin) in skeletal muscle. Passive force was increased in mutant fibers, showing that alternative structural components in a fiber can re-establish enhanced active stiffness in the absence of titin force enhancement. Collectively, the findings from this thesis show that titin-based force enhancement is an inherent property of skeletal muscle. The mechanism of titin force enhancement is crucial to sarcomere mechanics; as in its absence, sarcomeres generate less force and alternative structures to titin establish a comparable increase in active stiffness.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Biomedical Engineering

Grantor dc:publisher.institution

Graduate Studies

Year dc:date.issued

2017

Author dc:creator

• Powers, Krysta

Advisor dc:contributor.advisor

• Herzog, Walter

Committee members dc:contributor.committeemember

• Pollack, Gerald
• Schmidt, Tannin
• Syme, Douglas
• Nishikawa, Kiisa
• Shemanko, Carrie
• Federico, Salvatore

• Physiology
• Engineering--Biomedical

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

eng

DOI

http://dx.doi.org/10.11575/PRISM/24984

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:11023/3753