Genetic manipulation of key determinants of ion flow in glutamate receptorchannels in the mouse

Glutamate receptor channels are built around an ancient pore loop structure which defines the inner channel environment and which is connected to stru ctures for channel gating. This pore loop, which corresponds to the M2 regi on of the receptor subunits, enters the lipid bilayer from the intracellula r side in an a-helical configuration, then kinks to form a random coil and exits the lipid bilayer at the intracellular side. The narrow constriction of the channel is formed by amino acid residues that occupy a position shor tly after the end of the a-helical part of M2. These residues determine ion selectivity and conductance properties of the glutamate-gated channel. The critical residues are asparagines for NMDA receptor subunits and glutamine or arginine for AMPA and kainate receptor subunits. presence of arginine i n the critical channel position of AMPA and kainate receptors is controlled by site-selective RNA editing. To study the importance of these critical c hannel residues in the mouse, we introduced codon changes in the endogenous genes for NMDA and AMPA receptor subunits. Our results show that changes i n the critical channel position are not tolerated, but lead to early death. Therefore. the impact on adult synaptic function and plasticity by glutama te receptor channels with changed ion selectivity and conductance needs to be addressed by conditional expression of the mutant receptors. (C) 2001 El sevier Science B.V. All rights reserved.