Sarcoplasmic reticulum in globally stunned adult and newborn myocardium

Dysfunctional sarcoplasmic reticulum (SR) is thought to be involved in the phenomenon of myocardial stunning. Adult (3 to 4 kg) and neonatal (5 to 7 day old) rabbit hearts were examined for structural SR alterations following ischemic damage and myocardial stunning induced by incubation in Ringer's lactate at 39 degrees C. SR protein yield in neonate hearts (but not adult hearts) significantly decreased (p = 0.01) following 30 minutes of ischemia. In addition, calcium ATPase activity was reduced in both adult p = 0.006) and neonatal (p = 0.02) ischemic hearts. Examination of SR proteins by gel electrophoresis indicated that the levels of several proteins were altered by ischemia. In adult hearts, decreased levels of proteins of 22.5, 31.5, 33, and 83 kilodaltons (kd) were observed. In newborn ischemic hearts, decreases in 29, 37.5, 82, and 83 kd proteins were detected. The quantitative changes in calcium ATPase levels and SR protein content may adversely affect myocardial excitation-contraction coupling and relaxation, contributing to dysfunction in myocardial stunning.