Subcellular distribution and autophosphorylation of calcium/calmodulin-dependent protein kinase II-alpha in rat hippocampus in a model of ischemic tolerance.

A brief period of sublethal ischemia induces resistance to a subsequent, otherwise lethal, ischemic insult, a process named ischemic tolerance or preconditioning. A persistently disturbed cell signaling during reperfusion after cerebral ischemia has been proposed to contribute to ischemic cell death. Here, we report on the effect of ischemic preconditioning on the levels of the regulatory alpha-subunit of calcium/calmodulin protein kinase II and its phosphorylation in the hippocampal CA1 region. We found that during and following lethal cerebral ischemia, calcium/calmodulin protein kinase II-alpha is persistently translocated to cell membranes, where it becomes phosphorylated at threonine 286. In contrast, in the preconditioned brains the translocation and phosphorylation are transient and return to preischemic values after one day of reperfusion. At this time of reperfusion, the total level of calcium/calmodulin protein kinase II-alpha is significantly lower in preconditioned animals compared to the sham and non-conditioned animals. After one day of reperfusion, the level of calcium/calmodulin protein kinase II-alpha messenger RNA decreases in the non-conditioned brains, whereas it is unchanged in preconditioned brains. We conclude that, during and after ischemia, calcium/calmodulin protein kinase II-alpha is translocated to cell membranes and becomes phosphorylated at threonine 286. This could detrimentally influence cell survival by changing receptor function and ion channel conductance. Ischemic preconditioning prevents the persistent presence of calcium/calmodulin protein kinase II-alpha at cell membranes, presumably by enhancing its degradation, which could be part of a neuroprotective mechanism of ischemic tolerance.