The relationship between extracellular calcium and isovolumic systolic pressure in the Langendorff-perfused rat heart

ABSTRACT

The relationship between extracelular calcium concentration and isovolumic systolic pressure developed by left ventricles was studied in Langendorff-perfused rat hearts. At diastolic pressure lower than 15 mmHg the isovolumic systolic pressure increased when external calcium was changed from 0.5 to 1.25 mM. Pressure stabilized when external calcium was increased to 3.5 mM but then declined at 5 mM Ca**2+. At higher diastolic pressures (20 and 25 mmHg) systolic pressure increased only up to 1.25 mM Ca**2+, and declined with further increases in external calcium concentration. This behavior is probably related to "calcium overload" of the preparations at external calcium concentrations greater than 3.5 mM associated with a decreased perfusion pressure gradient at higher diastolic pressures