The Effects of Substrates on Contractility of Isolated Rat Atria Depressed by Hydrochloric Acid 1

Abstract

Summary

Addition of 20 mM hydrochloric acid to isolated rat atria results in a biphasic action on both contractility and pH. Initially contractility fell to 18% of the control value and pH fell from 7.4 to 5.6. This was followed, within 5 min, by a return of contractility to 102% of control and pH to 6.7. Following these initial changes the contractility fell slowly over the next 55 min to 50% of the control value despite the fact that the pH remained constant at 6.7. The initial rapid fall in contraction was correlated reasonably well with the changes in external hydrogen ion concentration and probably reflects the action of hydrogen ions on some readily accessible cellular compartment involved in the contractile process. The secondary, gradual decrease in contractility to 50% of control values in 1 hr is clearly not a function of extracellular hydrogen ion concentration as the pH remained constant at 6.7 during this period. The mechanism of this depression is involved with an inhibition of glycolysis since pyruvate is effective in overcoming the contractile depression whereas glucose and fructose are not.