Spinal cord ischemia reduces calcium/calmodulin-dependent protein kinase activity

Abstract

Calcium/calmodulin (Ca 2+/CaM)-dependent protein phosphorylation was evaluated in a rabbit spinal cord ischemia model. One hour of ischemia reduced particulate (5% of control) and cytosolic (35% of control) Ca 2+/CaM-dependent protein kinase activity significantly ( p < 0.01). In vitro phosphorylation of endogenous proteins by endogenous Ca 2+/CaM-dependent protein kinase showed that phosphorylation of 14 particulate and 7 cytosolic proteins was stimulated in the presence of Ca 2+/CaM in control tissue. However, after 1 hour of ischemia, Ca 2+/CaM-dependent protein phosphorylation was virtually absent in the particulate fraction and significantly reduced in the cytosol. When equal amounts of control and ischemic tissue samples were combined and assayed, Ca 2+/CaM-dependent protein kinase activity was 43% of control in particulate and 70% of control in cytosolic fractions. This suggests that reduced Ca 2+/CaM-dependent protein phosphorylation is probably not due to the presence of an inhibitory activity in ischemic tissue. These results show that the Ca 2+/CaM-dependent protein phosphorylation system is impaired after ischemia durations which cause irreversible damage. These altered phosphorylation reactions may play critical roles in mediating irreversible neurologic injury.