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Journal of Biomedicine and Biotechnology
Volume 2010 (2010), Article ID 725207, 20 pages
http://dx.doi.org/10.1155/2010/725207
Review Article

Mechanism of Catch Force: Tethering of Thick and Thin Filaments by Twitchin

Department of Molecular Physiology and Biophysics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA

Received 20 January 2010; Accepted 10 March 2010

Academic Editor: Henk L. M. Granzier

Copyright © 2010 Thomas M. Butler and Marion J. Siegman. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Catch is a mechanical state occurring in some invertebrate smooth muscles characterized by high force maintenance and resistance to stretch during extremely slow relaxation. During catch, intracellular calcium is near basal concentration and myosin crossbridge cyctng rate is extremely slow. Catch force is relaxed by a protein kinase A-mediated phosphorylation of sites near the N- and C- temini of the minititin twitchin (526 kDa). Some catch force maintenance car also occur together with cycling myosin crossbridges at submaximal calcium concentrations, but not when the muscle is maximally activated. Additionally, the link responsible for catch can adjust during shortening of submaximally activated muscles and maintain catch force at the new shorter length. Twitchin binds to both thick and thin filaments, and the thin filament binding shown by both the N- and Cterminal portions of twitchin is decreased by phosphorylation of the sites that regulate catch. The data suggest that the twitchin molecule itself is the catch force beanng tether between thick and thin filaments. We present a model for the regulation of catch in which the twitchin tether can be displaced from thin filaments by both (a) the phosphorylation of twitchin and (b) the attachment of high force myosin crossbridges.