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This Article Full Text Full Text (PDF) All Versions of this Article: 578/1/337    most recent jphysiol.2006.117770v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Colombini, B. Articles by Griffiths, P. J. Search for Related Content PubMed PubMed Citation Articles by Colombini, B. Articles by Griffiths, P. J. Related Collections Skeletal Muscle and Exercise

¹ Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze and Instituto Interuniversitario di Miologia (IIM), Viale G.B. Morgagni 63, I-50134 Firenze, Italy
² Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, UK

The aims of this study were to investigate the effects of solution tonicity on muscle properties, and to verify their consistence with the lever arm theory of force generation. Experiments were made in single muscle fibres and in fibre bundles from the frog, using both fast stretches and time-resolved X-ray diffraction, in isotonic Ringer solution (1T), hypertonic (1.4T) and hypotonic (0.8T) solutions. Fast stretches (0.4–0.6 ms duration and 16–25 nm per half-sarcomere (nm hs^–1) amplitude) were applied at various tensions during the force development in isometric tetani. Force increased during the stretch up to a peak (critical tension, P_c) at which it started to fall, in spite of continued stretching. In all solutions, P_c was proportional to the initial isometric tension developed. For a given isometric tension, P_c increased with solution tonicity and occurred at a precise sarcomere elongation (critical length, L_c) which also increased with tonicity. M3 meridional layer line intensity (I_M3) was measured during the application of sinusoidal length oscillations (1 kHz frequency, and about 2% fibre length amplitude) at tetanus plateau. I_M3 changed during the length oscillations in a sinusoidal manner in phase opposition to length changes, but a double peak distortion occurred at the peak of the release phase. The presence of the distortion, which decreased with tonicity, allowed calculation of the mean position of the myosin head (S1) during the oscillation cycle. In agreement with the lever arm theory, both X-ray diffraction and mechanical data show that solution tonicity affects S1 mean position and consequently crossbridge individual extension and force, with no effect on crossbridge number. The force needed to break the single crossbridge was insensitive to solution tonicity suggesting a non-ionic nature of the actomyosin bond.

(Received 21 July 2006; accepted after revision 29 September 2006; first published online 5 October 2006)
Corresponding author G. Cecchi: Dipartimento di Scienze Fisiologiche, Viale G.B. Morgagni 63, I-50134 Firenze, Italy. Email: giovanni.cecchi{at}unifi.it

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				B. Colombini, M. Nocella, G. Benelli, G. Cecchi, and M. A. Bagni Crossbridge properties during force enhancement by slow stretching in single intact frog muscle fibres J. Physiol., December 1, 2007; 585(2): 607 - 615. [Abstract] [Full Text] [PDF]