Effects of Strontium and Some Other Divalent Cations on Electrical and Mechanical Activity in Rat’s Portal Vein

  • Bengt Uvelius
  • Stefan B. Sigurdsson


Smooth muscle cells as well as striated muscle cells contain the proteins actin and myosin, which constitute the thin and thick myofilaments, respectively. The filaments are known to interact with one another, producing tension and/or shortening in both types of muscle. The energy necessary for this effect is obtained by splitting the ATP, catalyzed by actomyosin ATPase. When the skeletal muscle is in the relaxed state the ATPase activity is inhibited because the regulatory proteins, troponin and tropomyosin, suppress the interaction between myosin and actin (1). This inhibitory action is diminished when the intracellular Ca2+ concentration is increased above the very low resting level (< 10-7 M). In skeletal muscle these Ca2+ ions bind to troponin, causing a conformational change of the troponin-tropomyosin system making it possible for myosin to interact with actin sites and contraction starts. Activation of the contractile proteins in smooth muscle is also controlled via [Ca2+]i. It is not yet certain however if this is through a troponin-tropomyosin system similar to that in skeletal muscle or, as has recently been suggested, via a myosin-linked regulation (2).


Portal Vein Mechanical Activity Sarcoplasmic Reticulum Spike Activity Contractile Protein 


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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • Bengt Uvelius
    • 1
  • Stefan B. Sigurdsson
    • 1
  1. 1.Department of Physiology and BiophysicsUniversity of LundLundSweden

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