Mechanical Activation of NMDA Receptors

Project Summary/Abstract In the central nervous system, proteins experience mechanical cues that vary widely across developmental stage, cell type and location, and physiological state. When acting on membrane embedded ion-channel proteins, mechanical forces can modulate the ionic flux produced by the physiological activator or can directly gate the channel. In this application, we explore the hypothesis that mechanical forces can open NMDA receptors in the absence of the endogenous neurotransmitter glutamate. NMDA receptors are glutamate-gated excitatory receptors that are widely expressed at synaptic and extrasynaptic sites in brain and spinal cord, where they play key roles in physiology and pathology of excitatory synaptic development and plasticity. These key functions rely on unique biophysical properties such as, among others, slow kinetics, large calcium permeability, voltage-dependent Mg2+ block. In this application, we propose to pursue two interrelated aims. The first will be done in recombinant receptors and will examine the type and intensity of force that can gate the channel, the biophysical properties of the force-induced current (kinetics, conductance, permeability, etc.), and how the channel senses the mechanical cue. The second aim will be done in endogenous receptors (primary cultured neurons) and will begin to explore possible roles of mechanically gated NMDA receptor currents in physiologic and pathologic conditions. In both aims, we will use electrophysiology and optical methods to monitor NMDA receptor response, total and calcium current, to experimentally-controlled mechanical perturbations. These experiments will delineate what kind of mechanical forces can activate NMDA receptors and how the signals produced by force and by glutamate compare, and will help to predict the physiological and pathological situations where mechanical forces can shape neuronal function specifically by gating NMDA receptor currents. Given that the mechanosensitivity of NMDA receptor signals is yet uncharted, the results will lay the groundwork necessary to understand how NMDA receptors contribute to the impact of mechanical forces on synaptic function and dysfunction.