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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 102/5/1906    most recent 01169.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Smolensky, A. V. Articles by Ford, L. E. Search for Related Content PubMed PubMed Citation Articles by Smolensky, A. V. Articles by Ford, L. E.

The extensive length-force relationship of porcine airway smooth muscle

Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, Indiana

Submitted 17 October 2006 ; accepted in final form 12 February 2007

The full functional length range of trachealis muscle was measured to identify a precise reference length and to assess the length changes that the myofilament lattice can accommodate. The initial reference length (L_10%) was that where rest tension equaled 10% of total force (passive tension plus active force). Total force at this length served as a force reference (F_ref = 219 ± 12 kPa, N = 7). Muscles initially adapted at L_10% for 30–60 min had no rest tension when shortened to <0.9 L_10%. Passive tension rose steeply and linearly with slope 11.2 F_ref/L_10% at lengths >1.04 L_10%. Rest tension at 1.1 L_10% declined by <10% over 1 h. The steep slope and stability of rest tension at long lengths suggest that a parameter of the slope could serve as a precise, reproducible reference length. Active force was nearly constant at lengths 0.33–1.0 L_10% and declined steeply at lengths between 0.1 and 0.2 L_10%, extrapolating to zero at 0.076 L_10%. Muscles visibly reextended during relaxation at lengths <0.25 L_10%. At long lengths, force extrapolated to zero at 1.175 L_10%. The >15-fold length range (0.076–1.175 L_10%) for force generation and nearly constant force over a greater than threefold length range is likely produced by several structural accommodations, including filament sliding, an increased number of sliding filaments in series, and increased length of passive structures in series with the sliding filaments. Visible reextension during relaxation suggests that the lattice does not undergo plastic adaptations at lengths <25% L_10% and that lattice plasticity is limited to a three- to fourfold length range.

myofilament lattice; plasticity; length adaptation