Effects of perfusion pressure on coronary flow, myocardial Ca2+-washout, and the occurrence of calcium paradox in isolated perfused rat heart ventricles.

The influence of perfusion pressure (5-8 kPa) on coronary flow and myocardial Ca2+-washout during Ca2+-free perfusion, and on the occurrence of calcium paradox after subsequent Ca2+-reperfusion, was studied in isolated, stimulated, rat heart ventricles. During the Ca2+-free perfusion period (3 min) the following changes were observed: 1. Rapid cessation of ventricular contractions. 2. A pressure-dependent increase in diastolic rest tension. 3. A pressure-dependent increase increase in coronary flow rate. 4. A pressure-dependent increase in myocardial Ca2+-washout. Upon Ca2+-reperfusion all hearts failed to recover fully and the incidence of complete loss of ventricular contractility ("complete calcium paradox") increased with increasing perfusion pressure. Furthermore, a clear relationship between coronary flow and effluent-Ca2+-concentration (during Ca2+-free perfusion) and the occurrence of calcium paradox (upon Ca2+-reperfusion) was observed. The results suggested that the processes underlying the calcium paradox mechanism are influenced by the perfusion pressure, mainly via an effect on coronary flow during the Ca2+-free perfusion phase and through this effect on the rate and extent of myocardial Ca2+-washout.