Ischemia‐Induced Translocation of Ca2+/Calmodulin‐Dependent Protein Kinase II: Potential Role in Neuronal Damage

Abstract: The activities of Ca2+/calmodulin (CaM)‐dependent, Ca2+/phospholipid‐dependent, and cyclic AMP‐dependent protein kinases (CaM‐KII, PKC, and PKA, respectively) were determined in rat brains after global ischemia. Both CaM‐KII and PKC activities were significantly depressed in both hippocampal and cerebral cortical regions of ischemic animals, whereas no change was detected in PKA activity. The loss of CaM‐KII activity was more dramatic and more sustained than the loss of PKC activity and correlated with the duration of ischemia. These decreases in enzyme activity were found in both supernatant and pellet fractions from crude homogenates. When the supernatant and pellet were analyzed for the amount of CaM‐KII 50‐kDa protein, a significant decrease was detected in supernatant fractions that paralleled a gain in the amount of CaM‐KII in the pellet. Thus, the loss of CaM‐KII activity in the supernatant can be explained by translocation of the enzyme to the pellet. Whether inactivation of CaM‐KII occurs during or after the enzyme translocates from the supernatant to the pellet is unknown. Our results indicate that loss in CaM‐KII activity parallels neuronal damage associated with ischemia; down‐regulation of CaM‐KII activity coincided with translocation of the enzyme to the particulate fraction, and it is proposed that this may be, in fact, a mechanism for controlling excessive CaM‐KII phosphorylation.