Calcium inhibits willardiine-induced responses in kainate receptor GluR6(Q)/KA-2

Glutamate receptor ion channels: structure, regulation, and function

The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

Inhibition of willardiine-induced currents through rat GluR6/KA-2 kainate receptor channels by Zinc and other divalent cations

Heteromeric GluR6/KA-2 kainate receptor were expressed in HEK293 cells and an inhibition of willardiine-induced currents by cations was studied. Zinc was much more effective than Ca(2+), Ba(2+) and Mg(2+) at 235, 265 and 1382 fold increase in IC(50), respectively. The inhibition was not voltage-dependent. The present data showed that the binding site for the cations are different from that for willardiine and that the currents are inhibited by the cations via at least two distinct binding sites to Zn(2+) and Ca(2+). These data suggest that Zn(2+) play an important role in modulating glutamate receptors at the nervous system because of a presence of Zn(2+) and various effects of Zn(2+) on the receptors.

Characterisation of the effects of ATPA, a GLU(K5) receptor selective agonist, on excitatory synaptic transmission in area CA1 of rat hippocampal slices

Kainate receptors are involved in a variety of synaptic functions in the CNS including the regulation of excitatory synaptic transmission. Previously we described the depressant action of the GLU(K5) selective agonist (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid (ATPA) on synaptic transmission in the Schaffer collateral-commissural pathway of rat hippocampal slices. In the present study we report several new features of the actions of ATPA at this synapse. Firstly, the effectiveness of ATPA is developmentally regulated. Secondly, the effects of ATPA decline during prolonged or repeated applications. Thirdly, the effects of ATPA are not mediated indirectly via activation of GABA(A), GABA(B), muscarinic or adenosine A(1) receptors. Fourthly, elevating extracellular Ca(2+) from 2 to 4 mM antagonises the effects of ATPA. Some differences between the actions of ATPA and kainate on synaptic transmission in the Schaffer collateral-commissural pathway are also noted.