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Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice
06:22

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Published on: September 17, 2015

Carp (Cyprinus carpio) heart has a high sensitivity to the positive inotropic effect of strophanthidin despite

K Temma1, H Nagatomi, H Hirano

  • 1Department of Veterinary Pharmacology, Kitasato University, School of Veterinary Medicine and Animal Sciences, Aomori, Japan.

General Pharmacology
|January 1, 1987
PubMed

Insights

Heart muscle sensitivity to digitalis is determined by Na+, K+-ATPase affinity, not its force-frequency relationship. This study compared carp and guinea-pig hearts, revealing higher digitalis sensitivity in carp hearts due to greater enzyme affinity.

Area of Science:

  • Cardiovascular Physiology
  • Pharmacology
  • Biochemistry

Background:

  • The force-frequency relationship describes how heart muscle contraction changes with stimulation rate.
  • Digitalis compounds, like strophanthidin, increase heart muscle contraction (positive inotropic effect).
  • Na+, K+-ATPase is a key enzyme in heart cell membranes, targeted by digitalis.

Purpose of the Study:

  • To investigate the relationship between the force-frequency relationship and digitalis sensitivity in carp and guinea-pig hearts.
  • To compare the positive inotropic effects of strophanthidin and [3H]ouabain binding to Na+, K+-ATPase in these species.
  • To determine if digitalis sensitivity is linked to the force-frequency relationship or enzyme affinity.

Main Methods:

  • Studied carp hearts (negative force-frequency relationship) and guinea-pig hearts (positive force-frequency relationship).
  • Measured the positive inotropic effect of strophanthidin on ventricular muscle preparations.
  • Assessed specific binding of [3H]ouabain to sarcolemmal Na+, K+-ATPase.

Main Results:

  • Carp heart muscle showed high digitalis sensitivity (strophanthidin EC50 = 0.31 microM) and high [3H]ouabain binding affinity (Kd = 26 nM).
  • Strophanthidin's positive inotropic effect was not affected by beta-adrenergic blockade.
  • Carp hearts exhibited greater strophanthidin potency and [3H]ouabain affinity compared to guinea-pig hearts.

Conclusions:

  • A dissociation exists between the force-frequency relationship and heart muscle sensitivity to cardiotonic steroids.
  • Heart muscle's sensitivity to cardiotonic steroids is primarily dictated by the affinity of sarcolemmal Na+, K+-ATPase for these compounds.
  • This finding has implications for understanding cardiac glycoside action and potential therapeutic applications.

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