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Properties of the kainate channel in rat brain mRNA injected Xenopus oocytes: ionic selectivity and blockage
J C Randle1, P Vernier, A M Garrigues
1Laboratoire de Neurobiologie Cellulaire et Moleculaire, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Abstract:
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.
Insights
Researchers investigated kainate receptor channels using Xenopus oocytes. They found distinct properties in striatal and cerebellar kainate receptor channels, influencing ion selectivity and voltage dependence.
Area of Science:
- Neuroscience
- Molecular Biology
- Ion Channel Physiology
Background:
- Kainate receptors are ionotropic glutamate receptors crucial for synaptic transmission.
- Understanding their specific properties is vital for deciphering neuronal function and dysfunction.
Purpose of the Study:
- To characterize the functional properties of kainate receptor/channels expressed from rat striatal and cerebellar mRNA in Xenopus oocytes.
- To investigate the ion selectivity and voltage-dependent block of these channels.
Main Methods:
- Xenopus oocytes were injected with mRNA isolated from rat striatum and cerebellum.
- Electrophysiological recordings were performed to measure kainate-induced currents.
- Ion replacement and voltage-clamp techniques were used to analyze channel properties.
Main Results:
- Kainate induced inward currents competitively inhibited by GAMS.
- Striatal kainate receptors showed linear voltage-dependence, while cerebellar receptors exhibited inward rectification.
- The kainate channel is permeable to cations but not anions, with varying selectivity for monovalent cations.
- Large monovalent and divalent cations blocked the channel through voltage-dependent and weakly voltage-dependent mechanisms, respectively.
Conclusions:
- Kainate receptor/channels derived from rat striatum and cerebellum display distinct electrophysiological properties.
- These findings contribute to a proposed model of the kainate channel structure and function.