Functional Characteristics Of Iglur3 Ampa Receptor-Channels In Cell Attached Recordings

Ionotropic glutamate receptors (iGluR's) are ligand gated ion channels that mediate most of the fast excitatory neurotransmission in the CNS. Aberrant function of glutamate neurotransmission can lead to epilepsy and other neurodegenerative disorders. The extracellular ligand binding domain is a bilobal structure that binds an agonist and induces channel activation. Data from single channel recordings from homomeric AMPA receptor subtype (GluR3) in cell-attached patches were analyzed using QuB software to examine preliminary kinetic models of agonist dependent channel activity. Cell attached recordings were performed with both full and partial agonists on stably transfected HEK 293 cells. Amplitude analysis uncovered three conductance states, 15 pS, 27 pS, and 40 pS, in the presence of the full agonist, glutamate, as well as the partial agonists, fluorowillardiine, chlorowillardiine and nitrowillardiine. Different modes of activation ranging from low to high open probability exist for this channel. In the presence of the full agonist, glutamate, during a high mode of activation, the channel prefers to open to the intermediate and large conductance states. In the presence of the willardiine partial agonists, the channel opens more frequently to the smallest and intermediate conductance states. Kinetic modeling using maximum interval likelihood rate optimization revealed two time constants in each open state and at least three in the closed state for the partial and the full agonists. These data suggest the mode of channel activation is similar for both glutamate and willardiine compounds with varying rates of activation. Supported by NIH NS049223.