Phosphorylation state, solubility, and activity of calcium/calmodulin-dependent protein kinase II alpha in transient focal ischemia in mouse brain.

During and after middle cerebral artery occlusion in mice, CaMKII alpha protein was irreversibly translocated from the soluble to the Triton X-100-nonsoluble fraction. This decrease in solubility had a strong effect on activity: CaMKII alpha was almost completely inactivated after being translocated. Results from solubilization experiments suggest that different mechanisms underlie the conversion of CaMKII alpha protein from a soluble to a detergent nonsoluble form in ischemic as opposite to nonischemic tissue. Analysis of the phosphorylation state of CaMKII alpha revealed that in the total homogenate and the Triton X-100-nonsoluble fraction, CaMKII alpha phosphorylated at only one site was the dominant phosphorylated form, whereas in the soluble fraction CaMKII phosphorylated at two sites was the predominant phosphorylated species. Investigation of the mechanisms underlying ischemia-induced changes in the solubility of CaMKII alpha could help to elucidate processes triggered by transient focal cerebral ischemia that lead to neuronal cell injury.