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Ischemic brain injury in vitro: protective effects of NMDA receptor antagonists and calmidazolium
R Pohorecki1, G L Becker, P J Reilly
1Department of Anesthesiology, University of Nebraska Medical Center, Omaha 68198.
Abstract:
Excessive Ca2+ influx through NMDA receptor-coupled channels has been linked to neuronal cell death. Using an in vitro model of transient brain ischemia, we investigated possible protective effects of NMDA receptor antagonists ketamine or MK-801 and of calmidazolium, an inhibitor of intracellular Ca2(+)-activated proteins. Brain ischemia/recovery was simulated in isolated hippocampal slices and injury monitored by measurement of ATP levels. Omission of both glucose and oxygen (but not oxygen alone) for 20 min led to persistent ATP deficits after 4 h recovery. Addition of ketamine or MK-801 at 1 microM permitted ATP to recover within 1 h, as did addition of calmidazolium at 10 microM. Our findings are consistent with other reports that NMDA receptor antagonists can protect neuronal tissue from ischemic damage. The role of inappropriately activated Ca2(+)-mediated signaling processes in the mechanism(s) of such injury is suggested by the protection also seen with calmidazolium, an inhibitor of calmodulin and other structurally related proteins such as calpain(s) and protein kinase C. The inhibition of intracellular Ca2+ target proteins may be an alternative for protection of the brain against injury due to insults that activate NMDA receptors.
Insights
NMDA receptor antagonists like ketamine and MK-801, and calmidazolium, protected brain cells from ischemic damage by preventing excessive calcium influx. These findings suggest new therapeutic targets for brain injury.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- Excessive calcium (Ca2+) influx via NMDA receptors is implicated in neuronal cell death.
- Transient brain ischemia can lead to significant neuronal injury and energy deficits.
Purpose of the Study:
- To investigate the neuroprotective effects of NMDA receptor antagonists (ketamine, MK-801) and calmidazolium against ischemic brain injury.
- To explore the role of intracellular Ca2+-activated proteins in ischemic neuronal damage.
Main Methods:
- An in vitro model of transient brain ischemia using isolated hippocampal slices.
- Simulation of ischemia by omitting glucose and oxygen, followed by recovery monitoring.
- Measurement of adenosine triphosphate (ATP) levels to assess cellular injury.
- Administration of ketamine, MK-801, or calmidazolium during the recovery phase.
Main Results:
- Ischemia induced by 20 min of glucose and oxygen deprivation resulted in persistent ATP deficits.
- Ketamine and MK-801 (1 microM) restored ATP levels within 1 hour of recovery.
- Calmidazolium (10 microM) also effectively prevented ATP deficits, indicating protection.
Conclusions:
- NMDA receptor antagonists demonstrate neuroprotective effects against ischemic brain injury.
- Inhibition of intracellular Ca2+-activated proteins, such as calmodulin, calpain, and protein kinase C, offers an alternative neuroprotective strategy.
- Targeting Ca2+-mediated signaling pathways presents a potential therapeutic approach for brain insults involving NMDA receptor activation.