In this study, the heteromeric N-methyl-D-aspartate (NMDA) receptor channels composed of NR1a and NR2A subunits were expressed, purified, reconstituted into liposomes, and characterized by using the patch clamp technique. The protein exhibited the expected electrophysiological profile of activation by glutamate and glycine and internal Mg 2؉ blockade. We demonstrated that the mechanical energy transmitted to membrane-bound NMDA receptor channels can be exerted directly by tension developed in the lipid bilayer. Membrane stretch and application of arachidonic acid potentiated currents through NMDA receptor channels in the presence of intracellular Mg 2؉ . The correlation of membrane tension induced by either mechanical or chemical stimuli with the physiological Mg 2؉ block of the channel suggests that the synaptic transmission can be altered if NMDA receptor complexes experience local changes in bilayer thickness caused by dynamic targeting to lipid microdomains, electrocompression, or chemical modification of the cell membranes. The ability to study gating properties of NMDA receptor channels in artificial bilayers should prove useful in further study of structure-function relationships and facilitate discoveries of new therapeutic agents for treatment of glutamate-mediated excitotoxicity or analgesic therapies.arachidonic acid ͉ mechanosensation ͉ NMDA receptor ͉ patch clamp ͉ bilayer model T he ionotropic, glutamate-activated N-methyl-D-aspartate (NMDA) receptors are ligand-gated cation channels that play an important role in both physiological and pathological processes, including long-term potentiation and synaptic plasticity (1, 2), neuronal excitotoxicity, and cognitive deficits attributable to aging and pain (3-8). NMDA receptors are formed by heterooligomers of various NR1 and NR2 subunits (9). The secondary structure of the NMDA receptor monomer predicts four transmembrane segments (M1 to M4) with an extracellular N terminus and the C terminus located intracellularly. The M2 domain forms a cytoplasmic reentrant loop that lines the channel pore (9, 10). This region harbors a narrow constriction, forming the selectivity filter that controls voltage-dependent Mg 2ϩ block (10-12). The C-terminal tail binds to cytoskeletal complexes, including kinases and structural proteins, which further modulate the function of the NMDA receptor channel (3, 13).Mechanosensitivity is an important signal transduction mechanism that underlies a number of key biological processes ranging from cellular growth, cell volume and blood pressure regulation, touch, and pain sensation to cardiac arrhythmia, muscular dystrophy, and neuronal degeneration (14,15). In prokaryotes, the mechanosensory transduction is carried out by mechanosensitive (MS) channels of small (MscS-like) and large (MscL-like) conductance (14,16,17). Many eukaryotic ion channels can be gated by mechanical forces. For example, the signaling properties of some membrane proteins, including ion channels, can change dramatically after undergoing a dynamic targeting t...
