title: Excitotoxicity affects membrane potential and calmodulin kinase II activity in cultured rat cortical neurons.
abstract: OBJECTIVE
  Glutamate-induced excitotoxicity has been implicated as a causative factor for selective neuronal loss in ischemia and hypoxia. Toxic exposure of neurons to glutamate results in an extended neuronal depolarization that precedes delayed neuronal death. Because both delayed neuronal death and extended neuronal depolarization are dependent on calcium, we examined the effect of glutamate exposure on extended neuronal depolarization and calcium/calmodulin-dependent protein kinase II (CaM kinase II) activity.
  
  
  METHODS
  Three-week-old cortical cell cultures from embryonic rats were exposed to 500 microM glutamate and 10 microM glycine or to control medium for 10 minutes. Cells were examined for neuronal toxicity, electrophysiology, and biochemical alterations. In one set of experiments, whole-cell current clamp recording was performed throughout the experiment. In a parallel experiment, cortical cultures were allowed to recover from glutamate exposure for 1 hour, at which time the cells were homogenized and CaM kinase II activity was assayed using standard techniques.
  
  
  RESULTS
  Excitotoxic exposure to glutamate resulted in extended neuronal depolarization, which remained after removal of the glutamate. Glutamate exposure also resulted in delayed neuronal death, which was preceded by significant inhibition of CaM kinase II activity. The excitotoxic inhibition of CaM kinase II correlated with neuronal loss, was N-methyl-D-aspartate receptor-mediated, and was not due to autophosphorylation of the enzyme.
  
  
  CONCLUSIONS
  Glutamate-induced delayed neuronal toxicity correlates with extended neuronal depolarization and inhibition of CaM kinase II activity. Because inhibition of CaM kinase II activity significantly preceded the histological loss of neurons, the data suggest that modulation of CaM kinase II activity may be involved in the cascade of events resulting in loss of calcium homeostasis and delayed neuronal death.
authors.affiliation: Department of Neurology, Medical College of Virginia, Richmond 23298.
authors.forename: S B
authors.initials: SB
authors.lastname: Churn
authors.forename: S
authors.initials: S
authors.lastname: Sombati
authors.forename: W C
authors.initials: WC
authors.lastname: Taft
authors.forename: R J
authors.initials: RJ
authors.lastname: DeLorenzo
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D016923:Cell Death / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology*; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D005971:Glutamates / Q000633:toxicity*; D018698:Glutamic Acid; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000201:enzymology / Q000502:physiology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D013997:Time Factors
chemical_list: D005971:Glutamates; D047428:Protein Kinase Inhibitors; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases