Article
- The EMBO Journal (2004) 23, 772 - 779
- doi:10.1038/sj.emboj.7600097
Published online: 12 February 2004
Subject Categories:
A troponin switch that regulates muscle contraction by stretch instead of calcium
Bogos Agianian1,a,
Uro
Kr
i
1,2,a,
Feng Qiu1,b,
Wolfgang A Linke2,c,
Kevin Leonard1 and Belinda Bullard1
- European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg, Germany
- Institute of Physiology and Pathophysiology, University of Heidelberg, Heidelberg, Germany
Correspondence to:
Belinda Bullard, European Molecular Biology Laboratory. Meyerhofstrasse 1, D-69117 Heidelberg, Germany. Tel.: +49-6221-387-268; Fax: +49-6221-387-306; E-mail: bullard@embl.de
aThese authors contributed equally to this work
bPresent address: CABM, Rutgers University, Piscataway, NJ 08854, USA
cPresent address: University of Münster, Schlossplatz 5, D-48149 Münster, Germany
Received 17 October 2003; Accepted 5 December 2003
Abstract
The flight muscles of many insects have a form of regulation enabling them to contract at high frequencies. The muscles are activated by periodic stretches at low Ca2+ levels. The same muscles also give isometric contractions in response to higher Ca2+. We show that the two activities are controlled by different isoforms of TnC (F1 and F2) within single myofibrils. F1 binds one Ca2+ with high affinity in the C-terminal domain and F2 binds one Ca2+ in the C-terminal domain and one exchangeable Ca2+ in the N-terminal domain. We have characterised the isoforms and determined their effect on the development of stretch-activated and Ca2+-activated tension by replacing endogenous TnC in Lethocerus flight muscle fibres with recombinant isoforms. Fibres with F1 gave stretch-activated tension and minimal isometric tension; those with F2 gave Ca2+-dependent isometric tension and minimal stretch-activated tension. Regulation by a TnC responding to stretch rather than Ca2+ is unprecedented and has resulted in the ability of insect flight muscle to perform oscillatory work at low Ca2+ concentrations, a property to which a large number of flying insects owe their evolutionary success.
Keywords:
- Ca2+ regulation,
- insect flight muscle,
- stretch activation,
- troponin C
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