Abstract
Kainate receptors mediate glutamatergic signaling through both pre- and presynaptic receptors. Here, we studied the expression of the high affinity kainate receptor GluK5 in the mouse retina. Double-immunofluoresence labeling and electron microscopic analysis revealed a presynaptic localization of GluK5 in the outer plexiform layer. Unexpectedly, we found GluK5 almost exclusively localized to the presynaptic ribbon of photoreceptor terminals. Moreover, in GluK5-deficient mutant mice the structural integrity of synaptic ribbons was severely altered pointing to a novel function of GluK5 in organizing synaptic ribbons in the presynaptic terminals of rod photoreceptors.
Highlights
L-Glutamate is the major excitatory neurotransmitter in the brain
The discovery of selective antagonists, which enabled the isolation of kainate-receptor mediated currents [9,10,11], as well as their cloning and molecular characterization identified kainate receptor subunits as being distinct from subunits that contribute to AMPA and NMDA receptors [1, 12,13,14,15,16,17]
In the present study we aimed to explore in more detail the localization and possible role of the high affinity ionotropic glutamate receptor GluK5 in the mouse retina
Summary
Glutamatergic signals are mediated by metabotropic and ionotropic glutamate receptors. Based on their pharmacological properties the ion channel forming glutamate receptor family has been sub-divided into Kainate-, NMDA- and AMPA-type of ionotropic glutamate receptors [1, 2] with NMDA- and AMPA-type receptors being best known to mediate postsynaptic currents at excitatory synapses throughout the nervous system [3]. Five different kainate receptors subunits have been identified so far [1]. Based on sequence homologies and agonist binding properties they can be subdivided into the lowaffinity kainate receptor subunits GLUK1, GLUK2 and GLUK3 [18,19,20,21] and the high-affinity
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