A troponin switch that regulates muscle contraction by stretch instead of calcium

Bogos Agianian, Uroš Kržič, Feng Qiu, Wolfgang A. Linke, Kevin Leonard, Belinda Bullard

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)772-779
Number of pages8
JournalEMBO Journal
Issue number4
StatePublished - Feb 25 2004
Externally publishedYes


  • Ca regulation
  • Insect flight muscle
  • Stretch activation
  • Troponin C

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)


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