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Basic Research in Cardiology

, Volume 72, Issue 2–3, pp 133–139 | Cite as

Ca++ activation of ATPase activity, ATP-P1 exchange, and tension in briefly glycerinated heart muscle

  • H. J. Reiermann
  • J. W. Herzig
  • J. C. Rüegg
Original Contributions

Summary

In the course of Mg-dependent ATP splitting by heart actomyosin, an “energy rich” actomyosin-ADP complex is formed, which promotes the incorporation of phosphate32P into ATP in myofibrils. The rate of this ATP-phosphate exchange reaction depends on the extent of actin-myosin overlap which can be decreased by stretching glycerinated muscle fibres. In heart muscle, the calcium-ion dependence of this reaction is similar to that of the actomyosin ATPase, the tension, and “immediate fibre stiffness” (which is “hookean” and which is a measure for the number of myosin cross-bridges attached to and interacting with actin).

These findings suggest that calcium increases the amount of “contractile” actomyosin-ADP complexes. The proportionality between tension and ATPase activity further suggests that the rate-limiting step of the cross-bridge cycle (which determines the molecular turnover number, the “Wechselzahl” of the ATPase) is only little affected by calcium ions. These ions act by recruiting more bridges rather than by accelerating their reactions.

In addition, the depressing effect of inorganic phosphate on the contractile tension and its presumable role in energetic insufficiency will be discussed.

Keywords

Exchange Reaction ATPase Activity Heart Muscle Depressing Effect Turnover Number 
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.

Ca++-Aktivinerug von ATPase-Aktivität, ATP-Phosphat-Austausch und Kontraktionskraft in glycerinextrahierten Herzmuskelfasern

Zusammenfassung

Im Verlauf der Mg-aktivierten ATPase-Reaktion des Herzaktomyosins wird ein “energiereicher” Aktomyosin-ADP-Komplex gebildet, durch den die Inkorporation von32P-Phosphat in ATP begünstigt wird. Die Rate dieser ATP-Phosphat-Austauschreaktion ist abhängig vom Gradder Aktin-Myosin-Überlappung Im Herzmuskel ist die Ca++-Abhängigkeit dieser Reaktion ähnlich derjenigen der Aktomyosin-ATPase-Aktivität, der kontraktilen Spannung und der “immediate fibre stiffness”, die nachHuxley undSimmons (6) ein Maß für die Anzahl der zu jedem Moment angehefteten Querbrücken darstellt.

Die Ergebnisse weisen darauf hin, daß Calciumionen die Konzentration des “kontraktilen” Aktomyosin-ADP-Komplexes erhöhen. Die Proportionalität zwischen Spannung und ATPase-Aktivität ist ferner ein Indiz dafür, daß der ratenlimitierende Schritt des Querbrückenzyklus (der die Wechselzahl der kontraktilen ATPase bestimmt), nur wenig durch Ca++-Ionen beeinflußt wird. Calcium bewirkt eher eine Rekrutierung von Querbrücken als eine Beschleunigung ihrer Reaktion.

Zusätzlich wird der hemmende Effekt von anorganischem Phosphat auf die kontraktile Spannung im Zusammenhang mit der Entstehung der energetischen Insuffizienz diskutiert.

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Copyright information

© Dr. Dietrich Steinkopff Verlag 1977

Authors and Affiliations

  • H. J. Reiermann
    • 1
  • J. W. Herzig
    • 1
  • J. C. Rüegg
    • 1
  1. 1.2. Physiologisches Institut der Universität HeidelbergHeidelbergGermany

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