Influence of inorganic phosphate and energy state on force in skinned cardiac muscle from freshwater turtle and rainbow trout

J Comp Physiol B. 1999 Sep;169(6):439-44. doi: 10.1007/s003600050240.


Inorganic phosphate, which increases in the hypoxic cardiac cell, depresses force development. The cardiac muscle of freshwater turtle maintains a remarkably high contractility during hypoxia; this may involve a low sensitivity to phosphate. Therefore, freshwater turtle and rainbow trout were compared with regard to Ca(2+)-activated force in skinned atrial trabeculae in a bath containing 3 mM ATP buffered by 15 mM creatine phosphate in the presence of creatine kinase. For turtle, an increase in phosphate from 0 mM to either 6 mM or 12 mM reduced maximal force by 50% and 80% respectively, whereas the Ca2+ activity eliciting half maximal force (Ca0.5) was increased by 70% in 6 mM and could not be reliably recorded in 12 mM. For trout, the effects of phosphate were less pronounced. An increase from 0 mM to 12 mM did not affect maximal force significantly, but elevated Ca0.5 by 70%. Hypoxia increases ADP as creatine phosphate is shifted to creatine, therefore, creatine phosphate was changed from 15 mM to 3 mM and creatine from 0 mM to 12 mM. After these changes, the elevation of phosphate from 0 mM to 12 mM had no significant effects for either turtle or trout. In conclusion, the high performance of turtle cardiac muscle during hypoxia does not involve a low sensitivity of the contractile system to phosphate. In addition, the effect of increased phosphate seems to be offset by a concomitant increase in ADP.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / metabolism
  • Animals
  • Creatine / metabolism
  • Energy Metabolism
  • Hypoxia / metabolism
  • Hypoxia / physiopathology
  • In Vitro Techniques
  • Myocardial Contraction / drug effects*
  • Myocardial Contraction / physiology*
  • Myocardium / metabolism
  • Oncorhynchus mykiss / physiology*
  • Phosphates / metabolism
  • Phosphates / pharmacology*
  • Phosphocreatine / metabolism
  • Species Specificity
  • Turtles / physiology*


  • Phosphates
  • Phosphocreatine
  • Adenosine Diphosphate
  • Creatine