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Sarcomere function and crossbridge cycling

H E ter Keurs1

  • 1Department of Medicine, Faculty of Medicine, University of Calgary, Canada.

Advances in Experimental Medicine and Biology
|January 1, 1995
PubMed
Summary

Heart muscle power depends on calcium ions and sarcomere function. This study reveals how calcium concentration and sarcomere length influence heart muscle force and velocity, linking it to myosin interactions.

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Area of Science:

  • Cardiology
  • Muscle Physiology
  • Biophysics

Background:

  • Cardiac muscle power is determined by sarcomere force and velocity.
  • Sarcomere dynamics are regulated by intracellular calcium (Ca++) concentration.
  • Understanding these relationships is key to cardiac function.

Purpose of the Study:

  • To investigate the interplay between force (F), sarcomere length (SL), and velocity of shortening (V).
  • To correlate these mechanical properties with intracellular calcium concentration ([Ca++]i).
  • To elucidate the role of calcium binding and crossbridge kinetics in cardiac contractility.

Main Methods:

  • Experiments were conducted on isolated rat right ventricle trabeculae.
  • Measurements included force, sarcomere length, and shortening velocity.
  • Intracellular calcium concentration was monitored, and crossbridge kinetics were analyzed via ATP hydrolysis assays.

Main Results:

  • [Ca++]i transient during activation is significantly lower than total activating concentration.
  • The force-sarcomere length (F-SL) relationship is influenced by length-dependent calcium binding to Troponin-C.
  • Velocity of shortening (V) increases hyperbolically with decreasing load, and maximal velocity (Vo) is limited by crossbridge detachment rate.
  • Myosin iso-enzyme differences (V1 vs. V2) are attributed to variations in the S1 domain affecting actin binding.

Conclusions:

  • Cardiac force and velocity are intricately linked to intracellular calcium dynamics and sarcomere length.
  • Calcium binding to Troponin-C dictates the F-SL relationship, providing load independence.
  • Crossbridge detachment rate, influenced by myosin type, is a key determinant of maximal shortening velocity.

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