Influences of Protein Kinase A and D-Camp on Actin-Myosin Interaction and Energy Consumption of Cardiac Muscles

  • Yasutake Saeki
  • Takakazu Kobayashi
  • Kiyohiro Takigiku
  • Haruo Sugi
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 453)


To address controversies concerning the effects of β;-adrenergic stimulation on the rate of myocardial cross-bridge cycling, we measured three mechanical variables, isometric tension development, transient tension response to a step stretch in length (<1% of muscle length), maximum velocity of shortening, and a chemical variable, ATPase activity before and after treatment with the catalytic subunit of protein kinase A (PKA) in demem-branated rat right ventricular trabeculae, and also measured three mechanical variables before and after treatment with D-cAMP in intact ryanodine-induced tetanized preparations. PKA treatment (1 U/μl, 40 min) shifted the pCa-tension relation to the right from 5.41 to 5.26 at pCa50 (the [Ca2+] required for half maximal steady tension) without changing the steepness of the pCa-tension relation and the maximum tension. The rate of the transient tension changes was significantly increased after either PKA or D-cAMP treatment (5 mM, 15 min), regardless of the level of isometric tension. Vmax was increased for a given Ca2+ concentration after either the PKA or D-cAMP treatment, despite the reduced level of isometric tension. The PKA treatment also shifted the pCa-ATPase activity to the right slightly from 5.47 to 5.40 at pCa50, but increased the ATPase activity during a given level of steady isometric tension generation, resulting in an increased tension cost (ATPase activity/tension). These results suggest that, in rat right ventricular trabeculae, β-adrenergic stimulation may increase the rate of cross-bridge cycling by increasing the rate of cross-bridge detachment from actin through a PKA-mediated mechanism, although PKA reduces the Ca2+-sensitivity of the contractile system.


ATPase Activity Maximum Tension Isometric Tension Relaxing Solution Tension Cost 
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Copyright information

© Plenum Press, New York 1998

Authors and Affiliations

  • Yasutake Saeki
    • 1
  • Takakazu Kobayashi
    • 2
  • Kiyohiro Takigiku
    • 3
  • Haruo Sugi
    • 2
  1. 1.Department of Physiology School of Dental MedicineTsurumi UniversityTsurumi-ku, Yokohama 230Japan
  2. 2.Department of Physiology School of MedicineTeikyo UniversityTokyo 173Japan
  3. 3.Department of Pediatrics School of MedicineYokohama City UniversityYokohama 230Japan

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