Tetanically released zinc inhibits hippocampal mossy fiber calcium, zinc and synaptic responses.
At the zinc-enriched mossy fiber synapses from hippocampal CA3 area, electrical or chemical stimulation evokes zinc release from glutamatergic synaptic vesicles that may cause different pre- or postsynaptic actions. Besides zinc that can be co-localized with glutamate and GABA, the mossy fibers contain a very high density of ATP-sensitive potassium channels that are activated by zinc. We have investigated the possibility that intensely released zinc inhibits presynaptic calcium changes and consequently zinc and glutamate release. The studies were made combining optical recording of fast presynaptic calcium and zinc signals, using the fluorescent indicators Fura-2 and N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide, respectively, with measurements of field potentials. We have observed that strong tetanic stimulation caused posttetanic depressions of electrically induced presynaptic calcium and zinc signals and of synaptic responses, the depressions being blocked by zinc chelators. These results suggest that endogenously released zinc has an inhibitory role, mediated by presynaptic ATP-sensitive potassium channels and/or presynaptic calcium channels, that leads to the depression of zinc and glutamate release.
Quinta-Ferreira
M E
ME
Department of Physics and Center for Neurosciences of Coimbra, University of Coimbra, 3004-516 Coimbra, Portugal. emilia@ci.uc.pt
Matias
C M
CM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D004558:Electric Stimulation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D007202:Indicators and Reagents; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology; D019599:Mossy Fibers, Hippocampal / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009924:Organ Culture Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014105:Tosyl Compounds; D015032:Zinc / Q000378:metabolism*
D000634:Aminoquinolines; D002614:Chelating Agents; D018690:Excitatory Amino Acid Agonists; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D024661:Potassium Channels, Inwardly Rectifying; D014105:Tosyl Compounds; C061730:N-(6-methoxy-8-quinolyl)-4-toluenesulfonamide; D000255:Adenosine Triphosphate; D015032:Zinc; D002118:Calcium; D016257:Fura-2