The Journal of Neuroscience, November 1, 2002, 22(21):9203-9209
Barbiturates Induce Mitochondrial Depolarization and Potentiate
Excitotoxic Neuronal Death
Christopher M.
Anderson1,
Becky A.
Norquist1,
Sabino
Vesce2,
David G.
Nicholls2,
William H.
Soine3,
Shumin
Duan1, and
Raymond A.
Swanson1
1 Department of Neurology, University of California,
San Francisco, and Department of Veterans Affairs Medical Center, San
Francisco, California 94121, 2 Buck Institute for Research
on Aging, Novato, California 94945, and 3 Department of
Medicinal Chemistry, Virginia Commonwealth University, Richmond,
Virginia 23298
Barbiturates are widely used as anesthetics,
anticonvulsants, and neuroprotective agents. However, barbiturates
may also inhibit mitochondrial respiration, and mitochondrial
inhibitors are known to potentiate NMDA receptor-mediated
neurotoxicity. Here we used rat cortical cultures to examine the effect
of barbiturates on neuronal mitochondria and responses to NMDA receptor
stimulation. The barbiturates tested, secobarbital, amobarbital, and
thiamylal, each potentiated NMDA-induced neuron death at barbiturate
concentrations relevant to clinical and experimental use (100-300
µM). By using rhodamine-123 under quenching conditions,
barbiturates in this concentration range were shown to depolarize
neuronal mitochondria and greatly amplify NMDA-induced mitochondrial
depolarization. Barbiturate-induced mitochondrial depolarization was
increased by the ATP synthase inhibitor oligomycin, indicating that
barbiturates act by inhibiting electron transport sufficiently to cause
ATP synthase reversal. Barbiturates similarly amplified the effects of
NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence
mitochondrial potential or potentiate NMDA neurotoxicity or calcium
responses. However, all of the barbiturates attenuated NMDA-induced
calcium elevations and cell death when present at millimolar
concentrations. Whole-cell patch-clamp studies showed that these
effects may be attributable to actions at the cell membrane, resulting
in a block of NMDA-induced current flux at millimolar barbiturate
concentrations. Together, these findings reconcile previous reports of
opposing effects on barbiturates on NMDA neurotoxicity and show that
barbiturate effects on neuronal mitochondria can be functionally
significant. Effects of barbiturates on neuronal mitochondria should be
considered in experimental and clinical application of these drugs.
Key words:
amobarbital; N-glucoside amobarbital; secobarbital; calcium; glutamate; NMDA; rhodamine-123; fura-2
Copyright © 2002 Society for Neuroscience 0270-6474/02/22219203-07$05.00/0
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