Open Access

ARTICLE

Titin (Visco-) Elasticity in Skeletal Muscle Myofibrils

by JA. Herzog∗, TR. Leonard†^†, A. Jinha†^†, W. Herzog†, ‡^†

* Mount Allison University, Department of Biology, Sackville, NB, Canada.
† University of Calgary, Faculty of Kinesiology, Calgary, AB, Canada.
‡ Corresponding Author. Faculty of Kinesiology, 2500 University Dr. NW, Calgary, AB, T2N 1N4. Phone: 403-220-8525; Email: walter@kin.ucalgary.ca

Molecular & Cellular Biomechanics 2014, 11(1), 1-17. https://doi.org/10.3970/mcb.2014.011.001

Abstract

Titin is the third most abundant protein in sarcomeres and fulfills a number of mechanical and signaling functions. Specifically, titin is responsible for most of the passive forces in sarcomeres and the passive visco-elastic behaviour of myofibrils and muscles. It has been suggested, based on mechanical testing of isolated titin molecules, that titin is an essentially elastic spring if Ig domain un/refolding is prevented either by working at short titin lengths, prior to any unfolding of Ig domains, or at long sarcomere (and titin) lengths when Ig domain un/refolding is effectively prevented. However, these properties of titin, and by extension of muscles, have not been tested with titin in its natural structural environment within a sarcomere. The purpose of this study was to gain insight into the Ig domain un/refolding kinetics and test the idea that titin could behave essentially elastically at any sarcomere length by preventing Ig domain un/refolding during passive stretch-shortening cycles. Although not completely successful, we demonstrate here that titin’s visco-elastic properties appear to depend on the Ig domain un/refolding kinetics and that indeed, titin (and thus myofibrils) can become virtually elastic when Ig domain un/refolding is prevented.

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