Apparent desensitization of NMDA responses in Xenopus oocytes involves calcium-dependent chloride current.
N-Methyl-D-aspartate (NMDA) receptors were expressed and studied in Xenopus oocytes injected with rat brain RNA. NMDA application elicits a rapid inward current that decays in several seconds to a relatively stable level. This decay is reportedly due to desensitization. However, we found the early transient component could be evoked more than once during a single application of NMDA, suggesting that the receptor did not actually desensitize. Removal of external Ca2+, replacement of Ca2+ with Ba2+, or intracellular injection of EGTA abolished the transient component. Furthermore, a variety of Cl- channel blockers nearly eliminated the transient component and inhibited the plateau current as well. We propose that a significant portion of the NMDA current recorded in oocytes is carried by a transient inward Cl- current triggered by Ca2+ influx through the NMDA receptor/channel.
Department of Biological Sciences, University of Illinois, Chicago 60607.
J P
JP
Leonard
S R
SR
Kelso
D000818:Animals; D001921:Brain; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D015870:Gene Expression; D007473:Ion Channels / Q000502:physiology; D009865:Oocytes / Q000502:physiology*; D012313:RNA / Q000235:genetics; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000235:genetics / Q000502:physiology*; D014981:Xenopus
D002712:Chlorides; D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D012313:RNA; D002118:Calcium