Mechanisms and effects of intracellular calcium buffering on neuronal survival in organotypic hippocampal cultures exposed to anoxia/aglycemia or to excitotoxins.
Neuronal calcium loading attributable to hypoxic/ischemic injury is believed to trigger neurotoxicity. We examined in organotypic hippocampal slice cultures whether artificially and reversibly enhancing the Ca2+ buffering capacity of neurons reduces the neurotoxic sequelae of oxygen-glucose deprivation (OGD), whether such manipulation has neurotoxic potential, and whether the mechanism underlying these effects is pre- or postsynaptic. Neurodegeneration caused over 24 hr by 60 min of OGD was triggered largely by NMDA receptor activation and was attenuated temporarily by pretreating the slices with cell-permeant Ca2+ buffers such as 1, 2 bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester (BAPTA-AM). This pretreatment produced a transient, reversible increase in intracellular buffer content as demonstrated autoradiographically using slices loaded with 14C-BAPTA-AM and by confocal imaging of slices loaded with the BAPTA-AM analog calcium green-acetoxymethyl ester (AM). The time courses of 14C-BAPTA retention and of neuronal survival after OGD were identical, indicating that increased buffer content is necessary for the observed protective effect. Protection by Ca2+ buffering originated presynaptically because BAPTA-AM was ineffective when endogenous transmitter release was bypassed by directly applying NMDA to the cultures, and because pretreatment with the low Ca2+ affinity buffer 2-aminophenol-N,N,O-triacetic acid acetoxymethyl ester, which attenuates excitatory transmitter release, attenuated neurodegeneration. Thus, in cultured hippocampal slices, enhancing neuronal Ca2+ buffering unequivocally attenuates or delays the onset of anoxic neurodegeneration, likely by attenuating the synaptic release of endogenous excitatory neurotransmitters (excitotoxicity).
Abdel-Hamid
K M
KM
Playfair Neuroscience Unit, University of Toronto, Toronto, Ontario M5T-2S8, Canada.
Tymianski
M
M
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002250:Carbon Radioisotopes; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D006624:Hippocampus / Q000166:cytology*; D009410:Nerve Degeneration / Q000187:drug effects; D009474:Neurons / Q000737:chemistry / Q000166:cytology* / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology
D002021:Buffers; D002250:Carbon Radioisotopes; D002614:Chelating Agents; D018691:Excitatory Amino Acid Antagonists; D018696:Neuroprotective Agents; D009498:Neurotoxins; D018377:Neurotransmitter Agents; D016194:Receptors, N-Methyl-D-Aspartate; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D016291:Dizocilpine Maleate; D005947:Glucose; D010100:Oxygen; D002118:Calcium