Calcium/calmodulin-dependent protein kinase II containing a nuclear localizing signal is altered in retinal neurons exposed to N-methyl- d-aspartate

This study investigated N-methyl- d-aspartate (NMDA) mediated cell death and its possible regulation by calcium/calmodulin-dependent protein kinase II (CaMKII) in the adult rat retina. To investigate cell death, the terminal deoxyribonucleotidyltransferase (TdT)-mediated biotin-16-dUTP nick-end labelling (TUNEL) method was used to detect fragmented DNA in fixed tissue sections of rat retina. The TUNEL assay confirmed that apoptosis occurs in the inner nuclear layer (INL) and ganglion cell layer (GCL) following NMDA injection. The level of antibody binding to CaMKII-α, the activity of CaMKII, and the mRNA level for the α B subunit of CaMKII were found to be elevated for short time periods (30 min, 2 h) after a single intravitreal injection of NMDA. In contrast to this, there was a decrease in CaMKII activity and in the CaMKII-α B mRNA levels at longer time periods (24 h) following injection of NMDA. These effects were specific for the mRNA for the α B subunit, an alternatively spliced product of the CaMKII-α gene, that contains a nuclear localizing signal (NLS) known to target this protein to the nucleus. It is suggested that regulated expression of CaMKII-α B could be involved in the NMDA-mediated cell death in retinal neurons.