We identified a 45-kDa protein by 2D electrophoresis that was enhanced following pentylenetetrazol (PTZ)-mediated seizures. Mass-spectrography of this protein revealed the beta subunit of Ca2+/calmodulin-dependent protein kinase II (CaMKIIbeta), although no evidence for increase in bulk CaMKIIbeta transcripts was obtained. Physicochemical parameters of the 45-kDa species coincided with those of the type 7 isoform of CaMKIIbeta, CaMKIIbeta7. Reverse transcription-polymerase chain reaction revealed the existence of the CaMKIIbeta7 transcript in the mouse brain, but its RNA content was small and was not elevated by PTZ injection. CaMKIIbeta7 protein is thought to be accumulated in the nuclei of brain cells by PTZ-mediated seizure via some cellular mechanisms other than transcriptional and post-transcriptional regulation.