Journal of Comparative Physiology B

, Volume 157, Issue 5, pp 651–658 | Cite as

Tonic force maintenance after decay of active state in brachiopod smooth adductor muscle

  • Jerrel L. Wilkens


  1. 1.

    Contraction of smooth adductor muscles (SmA) in the brachiopod,Laqueus californicus, is followed by very slow relaxation (R1/2=3 min). The period during which the cross-bridges are in the active state extends from the time of activation to a short time after peak tension is reached. The delayed relaxation phase represents tension maintenance in the absence of the active state.

  2. 2.

    The contraction characteristics of these muscles were compared to those during the catch contractions of mollusc adductor muscles. The immediate elasticity of brachiopod SmA, defined as the change in tension in response to quick length changes, is the same during the contraction and relaxation phases. The immediate elasticity of mollusc catch muscles is greater during the tonic relaxation (catch) than the active contraction phase (Pfitzer and Rüegg 1982).

  3. 3.

    When exposed to CO2, the SmA, whether relaxed or during contraction, enter a reversible rigor-like state of stretch resistance. The immediate elastic modulus during these conditions was the same as during normal contractions.

  4. 4.

    The results indicate that the same physical linkages, probably actomyosin cross-bridges, are responsible for all phases of the contraction/relaxation cycle and also during CO2 induced rigor-like stiffness.



Adductor Muscle Active State Length Change Contraction Phase Physical Linkage 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



anterior byssus retractor muscle




artificial sea water




step length change


resting fiber length


recovery of tension 6 sec after length change


static elastic modulus


quick release of tension by step length change


half relaxation time


smooth adductor muscle


tension immediately preceding length change


immediate change in tension following step length change


immediate elastic modulus


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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Jerrel L. Wilkens
    • 1
  1. 1.Department of BiologyUniversity of CalgaryCalgaryCanada

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