Properties of the kainate channel in rat brain mRNA injected Xenopus oocytes: ionic selectivity and blockage.
The properties of kainate receptor/channels were studied in Xenopus oocytes injected with mRNA that was isolated from adult rat striatum and cerebellum and partially purified by sucrose gradient fractionation. Kainate (3-1000 microM) induced a smooth inward current that was competitively inhibited by gamma-D-glutamyl-aminomethanesulfonate (GAMS, 300 microM). In striatal mRNA-injected oocytes, the kainate current displayed nearly linear voltage-dependence and mean reversal potential (Er) of -6.1 +/- 0.5 mV. In cerebellar mRNA-injected oocytes; Er was nearly identical (-5.1 +/- 1.2 mV) but there was marked inward rectification of the kainate current. Ion replacement studies reveal that the kainate channel is selective for cations over anions, but relatively non-selective among small monovalent cations. Large monovalent cations such as tetrabutylammonium are impermeant and induce a non-competitive block of kainate current that is strongly voltage-dependent. Divalent cations are relatively impermeant in the kainate channel and Cd++ and other polyvalent metals were shown to block kainate current by a mechanism that is only weakly voltage-dependent. A model of the kainate channel is proposed based upon these observations.
Randle
J C
JC
Laboratoire de Neurobiologie Cellulaire et Moleculaire, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Vernier
P
P
Garrigues
A M
AM
Brault
E
E
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002412:Cations / Q000502:physiology; D002531:Cerebellum / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism; D004558:Electric Stimulation; D005971:Glutamates / Q000494:pharmacology; D005973:Glutamine / Q000031:analogs & derivatives*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009865:Oocytes / Q000378:metabolism / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D018092:Kainic Acid Receptors; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014982:Xenopus laevis
D002412:Cations; D005971:Glutamates; D005973:Glutamine; D007473:Ion Channels; D012333:RNA, Messenger; D018092:Kainic Acid Receptors; D017981:Receptors, Neurotransmitter; D013757:Tetraethylammonium Compounds; C042626:gamma-glutamylaminomethylsulfonic acid