Hydrogen ion changes and contractile behavior in the perfused rat heart

Abstract

The effect of acid-base alterations was analyzed using isolated rat hearts perfused at constant coronary perfusion pressure, and stimulated to contract at constant rate. The amount of shortening in the major axis and its derivative were measured to assess myocardial contractility. Both the 'respiratory' and 'metabolic' alterations affected the contractile behavior to the same extent. In the physiological range studied by us, acidosis depresses and alkalosis increases myocardial contraction. However, acidosis seems to depress contractility more than the enhancement produced by the same change in pH towards the alkalotic side. When either amount of shortening or max dl/dt was plotted as a function of hydrogen ion activity (aH+) a linear correlation was obtained, either with pure 'metabolic' or 'respiratory' acid-base induced alterations (correlation coefficients higher than - .95; P < .01). Our findings suggest that in the range studied by us, contract ion of the perfused rat he art following acid-base alterations, is a linear function of hydrogen ion activity.