INACTIVATION AND SUBCELLULAR REDISTRIBUTION OF CA-2-DEPENDENT PROTEINKINASE-II FOLLOWING SPINAL-CORD ISCHEMIA( CALMODULIN)

Reversible spinal cord ischemia in rabbits induced a rapid loss of Ca2 +/calmodulin-dependent protein kinase II (CaM kinase II) activity meas ured as incorporation of phosphate into exogenous substrates. About 70 % of the activity was lost from the cytosolic fraction of spinal cord homogenates after 15 min of ischemia preceding irreversible paraplegia , which takes 25 min in this model. The loss of enzyme activity correl ated with a loss of in situ renaturable autophosphorylation activity a nd a loss of CaM kinase II alpha and beta subunits in the cytosol dete cted by immunoblotting. CaM kinase II activity in the particulate frac tion also decreased but the protein levels of the a and beta subunits increased. Thus ischemia resulted in an inactivation of CaM kinase II and a sequential or concurrent subcellular redistribution of the enzym e. However, denaturation and renaturation in situ of the CaM kinase su bunits immobilized on membranes partly reversed the apparent inactivat ion of the enzyme in the particulate fraction. CaM kinase II activity was restored after reperfusion following short (less-than-or-equal-to 25 min) durations of ischemia but not after longer durations (60 min) that result in irreversible paraplegia. The ischemia-induced inactivat ion of CaM kinase II, which phosphorylates proteins regulating many ce llular processes, may be important in the cascade of events leading to delayed neuronal cell death.