Loss of calmodulin activity in cardiac sarcoplasmic reticulum after ischemia

Experiments were designed to evaluate whether cardiac ischemia affected the subcellular distribution of calmodulin activity. Major cellular fractions (nuclei, mitochondria, sarcoplasmic reticulum and cytosol) were isolated from globally ischemic hearts by differential centrifugation. Ischemia did not affect calmodulin activity in cell fractions other than sarcoplasmic reticulum, which showed a consistent and complete loss of activity. This site-specific loss of calmodulin activity may be one mechanism by which ischemia induces contractile dysfunction.