Interplay between expressed non-NMDA receptors and endogenous calcium-activated chloride currents in Xenopus laevis oocytes.
Current-voltage (I-V) relationships of glutamate receptors activated by the non-NMDA receptor agonist, kainate (KA), were determined in Xenopus laevis oocytes injected with either calf or chick brain mRNA. In most injected oocytes (n = 44; 84%), I-V plots to 80 microM KA exhibited inward rectification; however, in some oocytes (n = 7; 16%), the KA-evoked membrane current showed only slight outward rectification. A comparison between the resting membrane properties of injected oocytes with the KA-evoked currents revealed that weak outward rectification was often observed in oocytes possessing predominant voltage-activated calcium-dependent chloride currents (ICl(Ca)). In these oocytes, replacement of extracellular calcium (2 mM Ca2+) with magnesium ions (Mg2+), or the addition of the chloride channel blocker, anthracene-9-carboxylic acid (500 microM to 1 mM A9C), reduced ICl(Ca) and also altered the nature of the KA I-V plot revealing inward rectification. It is proposed that the responses mediated by expressed non-NMDA receptors may be influenced by the activation of endogenous calcium-dependent membrane currents in Xenopus laevis oocytes.
Department of Pharmacology, School of Pharmacy, London, UK.
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D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002642:Chick Embryo; D018118:Chloride Channels; D004594:Electrophysiology; D005260:Female; D007608:Kainic Acid / Q000494:pharmacology; D008274:Magnesium / Q000502:physiology; D008565:Membrane Proteins / Q000096:biosynthesis*; D009865:Oocytes / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis*; D014982:Xenopus laevis
D018118:Chloride Channels; D008565:Membrane Proteins; D012333:RNA, Messenger; D016194:Receptors, N-Methyl-D-Aspartate; D008274:Magnesium; D007608:Kainic Acid; D002118:Calcium