Acidosis, cardiac stunning and its prevention by oxygen

When during aerobic perfusion of the 5 Hz paced rat Langendorff heart, under constant aortic pressure of 8.3 kPa, the pH of the medium is changed from 7.5 to 7.0 a short period of positive inotropy is followed by a dramatic loss of contractility. The hearts, rapidly frozen after 10 min pH 7.0 perfusion, show moderate loss of high-energy phosphates and accumulation of lactate and glycerol-3-phosphate, indicative of tissue anaerobiosis. This can be overcome by including fluorocarbon, an O2 vehicle, in the media. The transient positive inotropy is interpreted as H(+)-induced release of plasmalemma-bound Ca2+ into the cytosol. The accompanying morphologic alterations are as described in this issue by Vandeplassche and Borgers (1990) and by Verkleij et al. (1990).